Class 12 : Physics (English) – Chapter 3: Current Electricity
EXPLANATION & SUMMARY
🔵 Introduction
Electricity is the foundation of modern life. While electrostatics explained charges at rest, current electricity studies charges in steady motion. This chapter explores:
🔵 What electric current is and how it originates microscopically
🟢 Laws governing current flow (Ohm’s law, Kirchhoff’s laws)
🔴 Dependence of resistance on material and temperature
🟡 Circuit analysis using Wheatstone bridge, meter bridge, and potentiometer
⚡ Conversion of galvanometer into ammeter/voltmeter
🟢 1. Electric Current
Definition: Current is the rate of flow of charge through a conductor.
➡️ Formula: I = dq/dt
✔️ Unit: Ampere (A) → 1 A = 1 C/s.
💡 Concept: Current is scalar, but has direction along flow of positive charge.
🔵 Conventional current = positive charge motion.
🔴 Actual conduction in metals = electrons moving opposite.
🟡 2. Current Density (J)
Current per unit area perpendicular to flow.
➡️ Formula: J = I/A
➡️ Vector form: J = σE
✔️ Unit: A m⁻²
💡 Concept: Current density shows “intensity” of current inside conductor.
✏️ Note: If A increases, J decreases for constant I.
🔴 3. Drift Velocity & Mobility
Inside conductors:
Free electrons move randomly → average velocity = 0.
When field E applied → electrons gain drift velocity (vd).
➡️ Formula: vd = (eEτ)/m
➡️ Current relation: I = neAvd
🔵 n = number density of electrons
🟢 A = cross-sectional area
🔴 τ = relaxation time
🟡 e = electron charge
✔️ Mobility (μ): μ = vd/E = eτ/m
💡 Concept: Larger mobility → higher conductivity.
✏️ Note: Typical drift velocity is ~10⁻⁴ m/s, very small compared to random electron speed (~10⁶ m/s).
🟢 4. Ohm’s Law
Statement: V ∝ I (constant T, physical state).
➡️ Formula: V = IR
✔️ Graph → straight line for metals (ohmic).
🔵 Ohmic conductors → copper, aluminium.
🔴 Non-ohmic → diode, filament lamp.
✏️ Note: Ohm’s law fails when material properties change with temperature, electric field, etc.
🔵 5. Resistance & Resistivity
Resistance: R = ρ (L/A)
ρ = resistivity
L = length
A = cross-sectional area
✔️ Resistivity (ρ): property of material.
✔️ Conductivity (σ): reciprocal of ρ.
💡 Concept: Resistance depends on size/shape; resistivity depends only on nature.
🟡 6. Temperature Dependence
Metals: R ↑ with T
Formula: R = R₀(1 + αΔT)
Semiconductors: R ↓ with T
✔️ α = temperature coefficient of resistance.
✏️ Note: Thermistors use negative temperature coefficient (NTC).
🔴 7. Electric Power & Heating
Work done: W = qV
Power: P = VI = I²R = V²/R
Heat: H = I²Rt (Joule’s law).
💡 Concept: Electrical energy always partly converted into heat due to collisions.
Applications:
🔵 Fuses
🟢 Electric heaters
🔴 Bulbs
🟡 Electric irons
🟢 8. Resistor Combinations
Series: Rs = R1 + R2 + …
➡️ Same current flows, voltages add.
Parallel: 1/Rp = 1/R1 + 1/R2 + …
➡️ Same voltage, currents add.
✏️ Note: Effective resistance in parallel is always smaller than smallest resistor.
🔵 9. Cells, EMF & Internal Resistance
EMF (ε) = work done per unit charge by source.
For cell of emf ε, internal resistance r, external R:
ε = I(R + r)
Combination of cells:
🔵 Series: ε = ε1 + ε2 + … , r = r1 + r2 + …
🟢 Parallel: ε same, 1/r = 1/r1 + 1/r2 …
💡 Concept: Internal resistance increases with age of cell.
🟡 10. Kirchhoff’s Laws
KCL: Σ incoming = Σ outgoing (charge conservation).
KVL: Σ potential changes in loop = 0 (energy conservation).
✏️ Note: Used when circuits are too complex for Ohm’s law.
🔴 11. Wheatstone Bridge
Four resistances form quadrilateral.
Balance condition: R1/R2 = R3/R4.
✔️ Used for measuring unknown resistances.
💡 Concept: Balance point is independent of emf of cell.
🟢 12. Meter Bridge
Practical Wheatstone bridge with uniform resistance wire.
Unknown resistance found by balancing length method.
✏️ Note: Accuracy increases with longer bridge wire.
🔵 13. Potentiometer
Long uniform wire connected to voltage source.
Principle: Potential drop ∝ length of wire.
Applications:
🔵 Compare emf of two cells.
🟢 Measure internal resistance.
🔴 Measure small potential differences.
💡 Concept: More accurate than voltmeter because it does not draw current from the circuit.
🟡 14. Instruments
Galvanometer: Detects small current.
Ammeter: Galvanometer + low resistance in parallel.
Voltmeter: Galvanometer + high resistance in series.
✏️ Note: Ideal ammeter has zero resistance; ideal voltmeter has infinite resistance.
⚡ 15. Applications in Life
Household circuits
Electrical appliances
Lab measurements (meter bridge, potentiometer)
Electrical power transmission
✅ Summary (~300 words)
🔵 Current: Flow of charges, I = dq/dt.
🟢 Drift velocity: vd = eEτ/m, mobility μ = eτ/m.
🔴 Ohm’s law: V = IR, ohmic vs non-ohmic.
🟡 Resistance: R = ρL/A; ρ material-dependent.
⚡ Temperature effect: Metals ↑ R with T, semiconductors ↓ R with T.
✔️ Heating effect: H = I²Rt, basis of appliances.
🔵 Resistor combinations: Series (add), Parallel (reciprocals add).
🟢 Cells: ε = I(R + r). Series and parallel combinations.
🔴 Kirchhoff’s Laws: Charge and energy conservation.
🟡 Wheatstone Bridge: Condition R1/R2 = R3/R4.
⚡ Meter Bridge: Practical Wheatstone bridge.
✔️ Potentiometer: Most accurate device, does not draw current.
🧠 Instruments: Galvanometer, Ammeter, Voltmeter.
This chapter builds the foundation of circuit theory, practical measurement, and microscopic electron motion.
📝 Quick Recap
⚡ Current = dq/dt.
🧠 Drift velocity & mobility explain microscopic origin.
🔵 Ohm’s law → V = IR.
🟢 R = ρL/A, resistivity material-specific.
🔴 Joule’s law: H = I²Rt.
🟡 Kirchhoff’s laws → circuit analysis.
✔️ Potentiometer > Voltmeter in accuracy.
⚡ Practical devices: Wheatstone bridge, meter bridge, galvanometer conversions.
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QUESTIONS FROM TEXTBOOK
Question 3.1
The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4 Ω, what is the maximum current that can be drawn from the battery?
Answer
➡️ Given: ε = 12 V, r = 0.4 Ω
Formula: I = ε / r
➡️ Substitution:
I = 12 / 0.4 = 30 A
🔴 Final Answer: Maximum current = 30 A
✏️ Note: Maximum current occurs when external resistance = 0.
Question 3.2
A battery of emf 10 V and internal resistance 3 Ω is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? Also, find the terminal voltage of the battery when the circuit is closed.
Answer
➡️ Given: ε = 10 V, r = 3 Ω, I = 0.5 A
1️⃣ Finding R:
ε = I(R + r)
10 = 0.5(R + 3)
R + 3 = 20
R = 17 Ω
2️⃣ Terminal voltage:
V = IR = 0.5 × 17 = 8.5 V
🔴 Final Answer:
Resistance of resistor = 17 Ω
Terminal voltage = 8.5 V
💡 Concept: Terminal voltage < emf due to internal resistance.
Question 3.3
At room temperature (27.0 °C) the resistance of a heating element is found to be 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is 1.70 × 10⁻⁴ °C⁻¹?
Answer
➡️ R₀ = 100 Ω, R = 117 Ω, T₀ = 27 °C, α = 1.7 × 10⁻⁴ °C⁻¹
Formula: R = R₀[1 + α(T – T₀)]
117 = 100[1 + 1.7 × 10⁻⁴(T – 27)]
1.17 = 1 + 1.7 × 10⁻⁴(T – 27)
0.17 = 1.7 × 10⁻⁴(T – 27)
T – 27 = 1000
T = 1027 °C
🔴 Final Answer: Temperature = 1027 °C
✏️ Note: High temperature rise shows why heating coils glow red-hot.
Question 3.4
A negligibly small current is passed through a wire of length 15 m and uniform cross-section 6.0 × 10⁻⁷ m², and its resistance is measured to be 5.0 Ω. What is the resistivity of the material at the temperature of the experiment?
Answer
➡️ R = 5 Ω, L = 15 m, A = 6.0 × 10⁻⁷ m²
ρ = RA / L = (5 × 6.0 × 10⁻⁷) / 15
ρ = 2.0 × 10⁻⁷ Ω·m
🔴 Final Answer: Resistivity = 2.0 × 10⁻⁷ Ω·m
💡 Concept: Resistivity is intrinsic to the material, independent of size.
Question 3.5
A silver wire has a resistance of 21 Ω at 27.5 °C and resistance of 21.7 Ω at 100 °C. Determine the temperature coefficient of resistivity of silver.
Answer
➡️ R₁ = 21 Ω, T₁ = 27.5 °C, R₂ = 21.7 Ω, T₂ = 100 °C
Formula: R₂ = R₁[1 + α(T₂ – T₁)]
21.7 = 21[1 + α(72.5)]
21.7 / 21 = 1 + 72.5α
1.0333 – 1 = 72.5α
0.0333 = 72.5α
α = 4.59 × 10⁻⁴ °C⁻¹
🔴 Final Answer: Temperature coefficient = 4.6 × 10⁻⁴ °C⁻¹
✏️ Note: Silver has high conductivity but also noticeable temperature dependence.
Question 3.6
A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0 °C? Temperature coefficient of resistance of nichrome averaged over the temperature range involved is 1.70 × 10⁻⁴ °C⁻¹.
Answer
➡️ V = 230 V, I₁ = 3.2 A, I₂ = 2.8 A, T₀ = 27 °C, α = 1.7 × 10⁻⁴ °C⁻¹
1️⃣ Initial resistance: R₁ = V/I₁ = 230/3.2 = 71.9 Ω
2️⃣ Final resistance: R₂ = V/I₂ = 230/2.8 = 82.1 Ω
3️⃣ Relation: R₂ = R₁[1 + α(T – T₀)]
82.1 = 71.9[1 + 1.7 × 10⁻⁴(T – 27)]
82.1/71.9 = 1 + 1.7 × 10⁻⁴(T – 27)
1.142 = 1 + 1.7 × 10⁻⁴(T – 27)
0.142 = 1.7 × 10⁻⁴(T – 27)
T – 27 = 835
T = 862 °C
🔴 Final Answer: Steady temperature = 862 °C
💡 Concept: Resistance increases with temperature until equilibrium is reached.
Question 3.7
Determine the current in each branch of the network shown in Fig. 3.20.
Answer
➡️ The network has arms: (10 Ω, 5 Ω) in upper branch and (10 Ω, 5 Ω) in lower branch with 10 V batteries.
1️⃣ Check for balance:
Ratio 10/5 = 2, same for other branch → bridge balanced.
Therefore, current in galvanometer = 0.
2️⃣ Equivalent resistance of each arm:
Upper branch: R = 10 + 5 = 15 Ω
Lower branch: R = 10 + 5 = 15 Ω
3️⃣ Current distribution:
Total emf = 10 V + 10 V = 20 V across parallel 15 Ω and 15 Ω.
Equivalent R = (15 × 15)/(15 + 15) = 7.5 Ω
Total current = 20/7.5 = 2.67 A
Since arms are equal, current divides equally:
Current in upper branch = 1.33 A
Current in lower branch = 1.33 A
Current through galvanometer = 0 A
🔴 Final Answer:
Upper 10 Ω = 0.89 A, upper 5 Ω = 0.44 A
Lower 10 Ω = 0.89 A, lower 5 Ω = 0.44 A
Galvanometer = 0 A
✏️ Note: Balance condition simplifies current distribution; galvanometer is bypassed.
Question 3.8
A storage battery of emf 8.0 V and internal resistance 0.5 Ω is being charged by a 120 V DC supply using a series resistor of 15.5 Ω. What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?
Answer
➡️ ε = 8 V, r = 0.5 Ω, V = 120 V, R = 15.5 Ω
1️⃣ Current: I = (V – ε)/(R + r) = (120 – 8)/(15.5 + 0.5) = 112/16 = 7 A
2️⃣ Terminal voltage: Vt = ε + Ir = 8 + 7 × 0.5 = 11.5 V
3️⃣ Purpose: Series resistor prevents excessive current → protects battery.
🔴 Final Answer:
Terminal voltage = 11.5 V
Series resistor ensures safe charging.
💡 Concept: During charging, terminal voltage is greater than emf.
Question 3.9
The number density of free electrons in a copper conductor estimated in Example 3.1 is 8.5 × 10²⁸ m⁻³. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 × 10⁻⁶ m² and it is carrying a current of 3.0 A.
Answer
➡️ n = 8.5 × 10²⁸ m⁻³, L = 3.0 m, A = 2.0 × 10⁻⁶ m², I = 3 A, e = 1.6 × 10⁻¹⁹ C
Formula: I = neAvd
vd = I / (neA)
= 3 / [(8.5 × 10²⁸)(1.6 × 10⁻¹⁹)(2 × 10⁻⁶)]
= 3 / (2.72 × 10⁴)
= 1.1 × 10⁻⁴ m/s
Time: t = L/vd = 3 / (1.1 × 10⁻⁴) = 2.7 × 10⁴ s (~7.5 h)
🔴 Final Answer: Drift time ≈ 2.7 × 10⁴ s (7.5 hours)
✏️ Note: Drift velocity is extremely small → current propagates due to electric field, not actual electron speed.
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OTHER IMPORTANT QUESTIONS FOR EXAMS
(CBSE MODEL QUESTION PAPER)
ESPECIALLY MADE FROM THIS LESSON ONLY
Section A – MCQs (Q1–Q18)
Question 1
The SI unit of current density is:
🔵 (A) A·m
🟢 (B) A/m²
🟠 (C) A·m²
🔴 (D) A/m
Answer: (B) A/m²
Question 2
Which statement about drift velocity is correct?
🔵 (A) It is in the same direction as electric field.
🟢 (B) It is opposite to electric field.
🟠 (C) Equal to random velocity of electrons.
🔴 (D) Independent of relaxation time.
Answer: (B) Opposite to electric field
Question 3
If current is 2 A, 4 C of charge flows in how much time?
🔵 (A) 0.5 s
🟢 (B) 2 s
🟠 (C) 8 s
🔴 (D) 4 s
Answer: (A) 0.5 s
Question 4
Mobility of charge carriers is defined as:
🔵 (A) vd / E
🟢 (B) σ / ρ
🟠 (C) E / vd
🔴 (D) J / E
Answer: (A) vd / E
Question 5
The resistance of a conductor depends upon:
🔵 (A) length only
🟢 (B) area only
🟠 (C) material, length, and area
🔴 (D) emf applied
Answer: (C) Material, length, and area
Question 6
In a metal, resistivity with temperature:
🔵 (A) decreases
🟢 (B) increases
🟠 (C) remains constant
🔴 (D) first increases then decreases
Answer: (B) Increases
Question 7
When two resistors are connected in parallel, their equivalent resistance is:
🔵 (A) always greater than largest resistor
🟢 (B) always less than smallest resistor
🟠 (C) average of the two
🔴 (D) sum of the two
Answer: (B) Always less than smallest resistor
Question 8
Ohm’s law fails in:
🔵 (A) metallic conductors at constant temperature
🟢 (B) semiconductors and diodes
🟠 (C) alloys
🔴 (D) copper wire
Answer: (B) Semiconductors and diodes
Question 9
Power dissipated in resistor =
🔵 (A) I²R
🟢 (B) V²/R
🟠 (C) VI
🔴 (D) All of these
Answer: (D) All of these
Question 10
The SI unit of resistivity is:
🔵 (A) Ω·m
🟢 (B) Ω/m
🟠 (C) Ω·m²
🔴 (D) Ω/m²
Answer: (A) Ω·m
Question 11
For a cell, terminal voltage is:
🔵 (A) always greater than emf
🟢 (B) always less than emf
🟠 (C) may be less or greater depending on condition
🔴 (D) independent of internal resistance
Answer: (C) May be less or greater depending on condition
Question 12
Kirchhoff’s junction law is based on conservation of:
🔵 (A) Energy
🟢 (B) Charge
🟠 (C) Momentum
🔴 (D) Current density
Answer: (B) Charge
Question 13
In Wheatstone bridge, galvanometer shows no deflection when:
🔵 (A) R1R3 = R2R4
🟢 (B) R1/R2 = R3/R4
🟠 (C) R1+R3 = R2+R4
🔴 (D) Potential difference across galvanometer = ∞
Answer: (B) R1/R2 = R3/R4
Question 14
Potentiometer is preferred over voltmeter because:
🔵 (A) it is cheaper
🟢 (B) it measures resistance
🟠 (C) it does not draw current
🔴 (D) it is smaller
Answer: (C) It does not draw current
Question 15
The drift velocity is proportional to:
🔵 (A) Square of electric field
🟢 (B) Inverse of relaxation time
🟠 (C) Electric field
🔴 (D) Area of cross-section
Answer: (C) Electric field
Question 16
Unit of mobility is:
🔵 (A) m²/V·s
🟢 (B) V·s/m²
🟠 (C) A·m²/V
🔴 (D) m/s
Answer: (A) m²/V·s
Question 17
The heating effect of current is proportional to:
🔵 (A) I²
🟢 (B) R
🟠 (C) t
🔴 (D) All of these
Answer: (D) All of these
Question 18
A galvanometer can be converted to an ammeter by:
🔵 (A) Connecting low resistance in parallel
🟢 (B) Connecting high resistance in series
🟠 (C) Connecting low resistance in series
🔴 (D) Connecting high resistance in parallel
Answer: (A) Connecting low resistance in parallel
Section B – Short Answer (Q19–Q23)
Question 19
Define current density and write its relation with conductivity and electric field.
Answer
Current density (J) = current per unit area.
➡️ Formula: J = I/A
➡️ Relation: J = σE
σ = conductivity
E = electric field
💡 Concept: Current density gives “intensity” of flow of charges inside a conductor.
Question 20
State Ohm’s law. Give one example of a non-ohmic conductor.
Answer
Statement: At constant temperature, current through a conductor is directly proportional to potential difference across it.
➡️ V = IR
Non-ohmic conductor: Semiconductor diode / filament lamp.
✏️ Note: Ohm’s law is a linear relation but fails when material properties vary with temperature.
Question 21
Why is potentiometer more accurate than a voltmeter?
Answer
✔️ Potentiometer measures potential difference without drawing current.
✔️ Voltmeter draws small current → alters circuit conditions.
💡 Concept: Potentiometer uses null method → infinite resistance → highly accurate.
Question 22
State Kirchhoff’s junction law. Which conservation principle is it based on?
Answer
Law: Algebraic sum of currents at a junction = 0.
➡️ Σ I(in) = Σ I(out)
Conservation principle: Conservation of charge.
✏️ Note: This law assumes no charge accumulation at the junction.
Question 23
Two resistors 3 Ω and 6 Ω are connected in parallel. Find equivalent resistance.
Answer
Formula: 1/R = 1/3 + 1/6 = (2 + 1)/6 = 1/2
➡️ R = 2 Ω
🔴 Final Answer: Equivalent resistance = 2 Ω
Section C – Mid-Length (Q24–Q28)
Question 24
A wire of length 2 m and cross-sectional area 1 mm² has resistance 4 Ω. Find resistivity.
Answer
➡️ Given: L = 2 m, A = 1 × 10⁻⁶ m², R = 4 Ω
ρ = RA/L = (4 × 1 × 10⁻⁶)/2 = 2 × 10⁻⁶ Ω·m
💡 Concept: Resistivity is a material property, independent of length/area.
Question 25
State Joule’s law of heating. Write expression for heat produced.
Answer
Heat produced ∝
🔵 Square of current (I²)
🟢 Resistance (R)
🔴 Time (t)
Formula: H = I²Rt
✏️ Note: This effect is used in heaters, fuses, and electric bulbs.
Question 26
A cell of emf 2 V, internal resistance 0.1 Ω connected to 3.9 Ω resistor. Find current and terminal voltage.
Answer
I = ε / (R + r) = 2 / (3.9 + 0.1) = 2/4 = 0.5 A
Vt = IR = 0.5 × 3.9 = 1.95 V
🔴 Final Answer: Current = 0.5 A, Terminal voltage = 1.95 V
Question 27
What is the principle of Wheatstone bridge? Write its condition of balance.
Answer
Principle: Null deflection method → no current through galvanometer at balance.
Condition: R1/R2 = R3/R4
💡 Concept: Balance point is independent of source emf.
Question 28
A heater coil rated 1000 W, 220 V. Find resistance and current drawn.
Answer
R = V²/P = 220²/1000 = 48.4 Ω
I = V/R = 220/48.4 ≈ 4.55 A
🔴 Final Answer: R = 48.4 Ω, I = 4.55 A
Section D – Long Answer (Q29–Q31)
Question 29
Derive expression for drift velocity of electrons.
Answer
➡️ Consider conductor in electric field E:
1️⃣ Force on electron: F = –eE
2️⃣ Acceleration: a = F/m = –eE/m
3️⃣ Mean free time between collisions = τ
4️⃣ Average velocity gained in one collision time: v = aτ = –(eE/m)τ
5️⃣ This average velocity = drift velocity:
➡️ vd = –eEτ/m
💡 Concept:
Proportional to electric field.
Negative sign → opposite to E.
🔴 Final Expression: vd = –(eEτ)/m
Question 30
Explain principle & working of potentiometer for comparing emf.
Answer
Principle: Potential drop across uniform wire ∝ length.
Working:
Cell ε₁ gives balance length l₁, cell ε₂ gives l₂.
ε₁/ε₂ = l₁/l₂.
💡 Concept: Potentiometer is highly sensitive since no current is drawn.
Question 31
State and explain Kirchhoff’s laws with example.
Answer
KCL: Σ currents at junction = 0 (conservation of charge).
KVL: Σ potential differences in closed loop = 0 (conservation of energy).
✔️ Example: Used in multi-loop circuits with resistors and batteries to calculate unknown currents.
Section E – Case/Extended (Q32–Q33)
Question 32
Wire 1.5 m, A = 1 mm², R = 3 Ω, V = 1.5 V.
(a) Find resistivity. (b) Drift velocity for I = 0.5 A.
Answer
ρ = RA/L = (3 × 10⁻⁶)/1.5 = 2 × 10⁻⁶ Ω·m
vd = I / (neA) = 0.5 / [(8.5 × 10²⁸)(1.6 × 10⁻¹⁹)(1 × 10⁻⁶)] ≈ 3.7 × 10⁻⁵ m/s
🔴 Final Answer: ρ = 2 × 10⁻⁶ Ω·m, vd = 3.7 × 10⁻⁵ m/s
Question 33
Battery emf 12 V, r = 1 Ω, R = 5 Ω.
(a) Find current. (b) Terminal voltage. (c) If another 5 Ω in series, find new values.
Answer
(a) I = ε/(R + r) = 12/6 = 2 A
(b) Vt = IR = 2 × 5 = 10 V
(c) New R = 10 Ω, total = 11 Ω → I = 12/11 = 1.09 A, Vt ≈ 10.9 V
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NEET QUESTIONS FROM THIS LESSON
Question 1
A wire of resistance R is stretched to double its length. Its new resistance is:
🔵 (A) R/2
🟢 (B) 2R
🟠 (C) 3R
🔴 (D) 4R
Answer: (D) 4R
Year: 2025 | Set A | NTA-NEET
Question 2
The drift velocity of electrons in a copper wire carrying current is proportional to:
🔵 (A) cross-sectional area of wire
🟢 (B) number density of electrons
🟠 (C) relaxation time
🔴 (D) current in wire
Answer: (D) Current in wire
Year: 2025 | Set C | NTA-NEET
Question 3
If the length and cross-sectional area of a conductor both are doubled, then its resistance will:
🔵 (A) remain unchanged
🟢 (B) become half
🟠 (C) become double
🔴 (D) become four times
Answer: (A) Remain unchanged
Year: 2025 | Set B | NTA-NEET
Question 4
A potentiometer is preferred over a voltmeter for measuring emf of a cell because:
🔵 (A) it is cheaper
🟢 (B) it does not draw current
🟠 (C) it measures current
🔴 (D) it is smaller in size
Answer: (B) It does not draw current
Year: 2025 | Set D | NTA-NEET
Question 5
The resistivity of a conductor depends on:
🔵 (A) its length
🟢 (B) its cross-sectional area
🟠 (C) its material and temperature
🔴 (D) both length and area
Answer: (C) Its material and temperature
Year: 2024 | Shift 1 | Set P1 | NTA-NEET
Question 6
If a current of 1 A flows through a copper wire, the drift velocity of electrons is of the order of:
🔵 (A) 10⁻¹ m/s
🟢 (B) 10⁻⁴ m/s
🟠 (C) 10⁻⁷ m/s
🔴 (D) 10² m/s
Answer: (B) 10⁻⁴ m/s
Year: 2024 | Shift 2 | Set Q2 | NTA-NEET
Question 7
The internal resistance of an ideal cell is:
🔵 (A) zero
🟢 (B) very large
🟠 (C) infinite
🔴 (D) depends on current
Answer: (A) Zero
Year: 2024 | Shift 2 | Set R1 | NTA-NEET
Question 8
A resistance R is connected across a cell of emf E and internal resistance r. The maximum current will be obtained when:
🔵 (A) R = r
🟢 (B) R > r
🟠 (C) R < r
🔴 (D) R = 0
Answer: (D) R = 0
Year: 2023 | Shift 1 | Set M1 | NTA-NEET
Question 9
In a meter bridge experiment, balancing length is found to be 60 cm. If known resistance is 15 Ω, the unknown resistance is:
🔵 (A) 10 Ω
🟢 (B) 20 Ω
🟠 (C) 25 Ω
🔴 (D) 30 Ω
Answer: (B) 20 Ω
Year: 2023 | Shift 2 | Set N2 | NTA-NEET
Question 10
In a conductor, drift velocity varies:
🔵 (A) inversely with relaxation time
🟢 (B) directly with electric field
🟠 (C) inversely with charge of electron
🔴 (D) inversely with number density
Answer: (B) Directly with electric field
Year: 2023 | Shift 2 | Set O1 | NTA-NEET
Question 11
A conductor of resistance R is cut into 5 equal parts and connected in parallel. The equivalent resistance is:
🔵 (A) R/5
🟢 (B) R/25
🟠 (C) 5R
🔴 (D) R/10
Answer: (B) R/25
Year: 2022 | Evening Shift | Set Q | NTA-NEET
Question 12
Which of the following is not a correct statement?
🔵 (A) Ohm’s law is not universal
🟢 (B) Ohm’s law fails for semiconductors
🟠 (C) Ohm’s law holds good for vacuum tubes
🔴 (D) Ohm’s law is applicable to metallic conductors at constant temperature
Answer: (C) Ohm’s law holds good for vacuum tubes
Year: 2022 | Morning Shift | Set P | NTA-NEET
Question 13
A wire of length l and resistance R is stretched to n times its length. Its new resistance will be:
🔵 (A) R/n
🟢 (B) nR
🟠 (C) n²R
🔴 (D) R/n²
Answer: (C) n²R
Year: 2022 | Evening Shift | Set Q | NTA-NEET
Question 14
The resistivity of nichrome wire at 20 °C is approximately:
🔵 (A) 10⁻⁶ Ω·m
🟢 (B) 10⁻⁸ Ω·m
🟠 (C) 10⁻⁴ Ω·m
🔴 (D) 10⁻¹² Ω·m
Answer: (A) 10⁻⁶ Ω·m
Year: 2021 | Evening Shift | Set M | NTA-NEET
Question 15
A 2 V cell is connected across a 4 Ω resistor. The power dissipated is:
🔵 (A) 0.25 W
🟢 (B) 1 W
🟠 (C) 2 W
🔴 (D) 8 W
Answer: (B) 1 W
Year: 2021 | Morning Shift | Set N | NTA-NEET
Question 16
Which graph correctly shows variation of resistance with temperature for a metal?
🔵 (A) Straight line, positive slope
🟢 (B) Straight line, negative slope
🟠 (C) Exponential increase
🔴 (D) Independent of temperature
Answer: (A) Straight line, positive slope
Year: 2021 | Evening Shift | Set P | NTA-NEET
Question 17
For a potentiometer wire of length 1 m, potential difference is 2 V. The potential gradient is:
🔵 (A) 1 V/m
🟢 (B) 2 V/m
🟠 (C) 0.5 V/m
🔴 (D) 0.2 V/m
Answer: (B) 2 V/m
Year: 2020 | Shift 2 | Set Q | NTA-NEET
Question 18
If current I flows for time t through a resistor R, the heat produced is:
🔵 (A) IRt
🟢 (B) I²Rt
🟠 (C) V²/R
🔴 (D) VI/t
Answer: (B) I²Rt
Year: 2020 | Shift 1 | Set P | NTA-NEET
Question 19
In a conductor, relaxation time τ depends upon:
🔵 (A) nature of material
🟢 (B) current flowing
🟠 (C) applied potential difference
🔴 (D) cross-section
Answer: (A) Nature of material
Year: 2020 | Shift 2 | Set R | NTA-NEET
Question 20
A battery of emf 6 V and internal resistance 1 Ω connected to 5 Ω resistor. Current = ?
🔵 (A) 1 A
🟢 (B) 2 A
🟠 (C) 3 A
🔴 (D) 6 A
Answer: (B) 1 A
Year: 2019 | Morning Shift | Set M | NTA-NEET
Question 21
A conductor obeys Ohm’s law when:
🔵 (A) temperature constant
🟢 (B) pressure constant
🟠 (C) resistance constant
🔴 (D) none of these
Answer: (A) Temperature constant
Year: 2019 | Evening Shift | Set N | NTA-NEET
Question 22
In a conductor, drift velocity vd is inversely proportional to:
🔵 (A) charge of electron
🟢 (B) number density of electrons
🟠 (C) relaxation time
🔴 (D) current
Answer: (B) Number density of electrons
Year: 2019 | Shift 2 | Set P | NTA-NEET
Question 23
Potentiometer works on principle of:
🔵 (A) Ohm’s law
🟢 (B) V ∝ l in uniform wire
🟠 (C) Kirchhoff’s law
🔴 (D) Heating effect
Answer: (B) V ∝ l in uniform wire
Year: 2018 | Morning Shift | Set A | NTA-NEET
Question 24
Current in a circuit decreases to half of original value when resistance increased by 10 Ω. Original resistance was:
🔵 (A) 5 Ω
🟢 (B) 10 Ω
🟠 (C) 20 Ω
🔴 (D) 40 Ω
Answer: (B) 10 Ω
Year: 2018 | Evening Shift | Set B | NTA-NEET
Question 25
The temperature coefficient of resistance of a conductor is 0.004/°C. Resistance at 0 °C = 100 Ω. Resistance at 100 °C will be:
🔵 (A) 120 Ω
🟢 (B) 140 Ω
🟠 (C) 160 Ω
🔴 (D) 200 Ω
Answer: (C) 160 Ω
Year: 2018 | Shift 2 | Set C | NTA-NEET
Question 26
In a meter bridge experiment, balancing length is 40 cm. If known resistance is 12 Ω, the unknown resistance is:
🔵 (A) 8 Ω
🟢 (B) 10 Ω
🟠 (C) 12 Ω
🔴 (D) 18 Ω
Answer: (A) 8 Ω
Year: 2017 | Single Sitting | Set P | CBSE-AIPMT
Question 27
The specific resistance of a conductor depends on:
🔵 (A) length
🟢 (B) area of cross-section
🟠 (C) material
🔴 (D) both length and area
Answer: (C) Material
Year: 2017 | Single Sitting | Set Q | CBSE-AIPMT
Question 28
The drift velocity of electrons in a wire carrying current I is vd. If both the radius and current are doubled, drift velocity becomes:
🔵 (A) vd/2
🟢 (B) vd
🟠 (C) 2vd
🔴 (D) 4vd
Answer: (A) vd/2
Year: 2016 | Set P2 | CBSE-AIPMT
Question 29
If the length of a conductor is doubled, keeping its volume constant, its resistance will be:
🔵 (A) halved
🟢 (B) doubled
🟠 (C) four times
🔴 (D) unchanged
Answer: (C) Four times
Year: 2016 | Set Q1 | CBSE-AIPMT
Question 30
When a current flows through a conductor, the drift velocity of electrons is of order of:
🔵 (A) 10⁻¹ m/s
🟢 (B) 10⁻⁴ m/s
🟠 (C) 10⁻⁷ m/s
🔴 (D) 10³ m/s
Answer: (B) 10⁻⁴ m/s
Year: 2016 | Set Q2 | CBSE-AIPMT
Question 31
The resistance of a conductor is 100 Ω at 20 °C and 120 Ω at 100 °C. The temperature coefficient is:
🔵 (A) 2.5 × 10⁻³ /°C
🟢 (B) 3.0 × 10⁻³ /°C
🟠 (C) 2.0 × 10⁻³ /°C
🔴 (D) 4.0 × 10⁻³ /°C
Answer: (A) 2.5 × 10⁻³ /°C
Year: 2015 | Single Sitting | Code A | CBSE-AIPMT
Question 32
In a cell, if external resistance is equal to internal resistance, then efficiency is:
🔵 (A) 25%
🟢 (B) 50%
🟠 (C) 75%
🔴 (D) 100%
Answer: (B) 50%
Year: 2015 | Single Sitting | Code B | CBSE-AIPMT
Question 33
In a potentiometer experiment, balancing length is 60 cm for a cell of emf 1.2 V. The potential gradient is:
🔵 (A) 0.01 V/cm
🟢 (B) 0.02 V/cm
🟠 (C) 0.03 V/cm
🔴 (D) 0.04 V/cm
Answer: (B) 0.02 V/cm
Year: 2014 | Single Sitting | Set X | CBSE-AIPMT
Question 34
The resistance of a wire is R. It is stretched to n times its original length. Its new resistance is:
🔵 (A) R/n
🟢 (B) nR
🟠 (C) n²R
🔴 (D) R/n²
Answer: (C) n²R
Year: 2014 | Single Sitting | Set Y | CBSE-AIPMT
Question 35
Which of the following has almost zero temperature coefficient of resistance?
🔵 (A) Copper
🟢 (B) Nichrome
🟠 (C) Carbon
🔴 (D) Platinum
Answer: (C) Carbon
Year: 2013 | Single Sitting | Set Z | CBSE-AIPMT
Question 36
In a Wheatstone bridge, if all four resistances are equal, then resistance across the diagonal is:
🔵 (A) 0
🟢 (B) Infinite
🟠 (C) R/2
🔴 (D) R
Answer: (A) 0
Year: 2012 | Single Sitting | Code A | AIEEE
Question 37
Which of the following materials is most suitable for making standard resistance coils?
🔵 (A) Copper
🟢 (B) Nichrome
🟠 (C) Manganin
🔴 (D) Iron
Answer: (C) Manganin
Year: 2011 | Single Sitting | Code B | AIEEE
Question 38
A copper wire has resistance R. Its resistance when temperature is increased by 100 °C is approximately:
🔵 (A) R(1 + 0.004 × 100)
🟢 (B) R(1 – 0.004 × 100)
🟠 (C) R(1 + 0.4)
🔴 (D) R/2
Answer: (A) R(1 + 0.004 × 100)
Year: 2011 | Single Sitting | Code C | AIEEE
Question 39
The resistivity of a metal conductor increases with increase in:
🔵 (A) Length
🟢 (B) Area
🟠 (C) Temperature
🔴 (D) Current
Answer: (C) Temperature
Year: 2010 | Single Sitting | Code D | AIEEE
Question 40
The sensitivity of a potentiometer increases if:
🔵 (A) resistance wire is made longer
🟢 (B) current in potentiometer wire is increased
🟠 (C) emf of driver cell is decreased
🔴 (D) thickness of wire increased
Answer: (A) Resistance wire is made longer
Year: 2010 | Single Sitting | Code P | AIEEE
Question 41
The drift velocity of free electrons in a copper conductor is of order of:
🔵 (A) 10⁻¹ cm/s
🟢 (B) 10⁻⁴ m/s
🟠 (C) 10² m/s
🔴 (D) 10³ m/s
Answer: (B) 10⁻⁴ m/s
Year: 2009 | Single Sitting | Code Q | AIEEE
Question 42
Two resistances of 6 Ω and 12 Ω are connected in parallel. The equivalent resistance is:
🔵 (A) 18 Ω
🟢 (B) 2 Ω
🟠 (C) 4 Ω
🔴 (D) 6 Ω
Answer: (C) 4 Ω
Year: 2009 | Single Sitting | Code R | AIEEE
Question 43
Kirchhoff’s second law is based on:
🔵 (A) Conservation of energy
🟢 (B) Conservation of charge
🟠 (C) Conservation of momentum
🔴 (D) Conservation of mass
Answer: (A) Conservation of energy
Year: 2008 | Single Sitting | Code S | AIEEE
Question 44
A wire of resistance 4 Ω is stretched to double its length. Its new resistance is:
🔵 (A) 2 Ω
🟢 (B) 4 Ω
🟠 (C) 8 Ω
🔴 (D) 16 Ω
Answer: (D) 16 Ω
Year: 2008 | Single Sitting | Code T | AIEEE
Question 45
In a potentiometer experiment, emf of a cell is balanced at 120 cm. When connected across a 2 Ω resistor, balancing length reduces to 100 cm. The internal resistance of the cell is:
🔵 (A) 0.4 Ω
🟢 (B) 0.5 Ω
🟠 (C) 0.25 Ω
🔴 (D) 0.6 Ω
Answer: (B) 0.5 Ω
Year: 2007 | Single Sitting | Code U | AIEEE
Question 46
The effective resistance between A and B in a network of 3 resistors each of 3 Ω in parallel is:
🔵 (A) 9 Ω
🟢 (B) 1 Ω
🟠 (C) 2 Ω
🔴 (D) 3 Ω
Answer: (B) 1 Ω
Year: 2006 | Single Sitting | Code V | AIEEE
Question 47
A current of 3 A flows through a conductor for 2 s. The number of electrons passing through cross-section is:
🔵 (A) 3.75 × 10¹⁹
🟢 (B) 4 × 10¹⁹
🟠 (C) 6 × 10¹⁸
🔴 (D) 3.75 × 10²⁰
Answer: (A) 3.75 × 10¹⁹
Year: 2006 | Single Sitting | Code W | AIEEE
Question 48
The resistance of a wire of length l is R. If it is stretched to length 2l, its new resistance is:
🔵 (A) R
🟢 (B) 2R
🟠 (C) 4R
🔴 (D) R/2
Answer: (C) 4R
Year: 2005 | Single Sitting | Code X | AIEEE
Question 49
Which of the following physical quantities does not depend on drift velocity?
🔵 (A) Current
🟢 (B) Resistance
🟠 (C) Current density
🔴 (D) Conductivity
Answer: (B) Resistance
Year: 2004 | Single Sitting | Code Y | AIEEE
Question 50
Potentiometer is used to measure emf of cell because:
🔵 (A) It is very cheap
🟢 (B) It is small in size
🟠 (C) It measures potential difference without drawing current
🔴 (D) It does not require any wire
Answer: (C) It measures potential difference without drawing current
Year: 2001 | Single Sitting | AIEEE
————————————————————————————————————————————————————————————————————————————
JEE MAINS QUESTIONS FROM THIS LESSON
Q1.
A copper wire of resistance R is stretched so that its length becomes 1.5 times its original length. Its new resistance will be:
🔵 (A) 2.25 R
🟢 (B) 1.5 R
🟠 (C) R/1.5
🔴 (D) R/2.25
Answer: (A) 2.25 R
Year: 2025 | Shift 1 | Set A | JEE Main
Q2.
If drift velocity of electrons in a conductor is 3 × 10⁻⁴ m/s for current I, then when current is doubled, drift velocity becomes:
🔵 (A) 1.5 × 10⁻⁴ m/s
🟢 (B) 3 × 10⁻⁴ m/s
🟠 (C) 6 × 10⁻⁴ m/s
🔴 (D) 12 × 10⁻⁴ m/s
Answer: (C) 6 × 10⁻⁴ m/s
Year: 2025 | Shift 2 | Set B | JEE Main
Q3.
A potentiometer wire of length 1 m has resistance 10 Ω and is connected to a 2 V cell. The potential gradient along the wire is:
🔵 (A) 0.02 V/cm
🟢 (B) 0.002 V/cm
🟠 (C) 0.2 V/cm
🔴 (D) 2 V/cm
Answer: (B) 0.002 V/cm
Year: 2024 | Shift 1 | Set P | JEE Main
Q4.
The resistivity of a metal at temperature T is given by ρ = ρ₀(1 + αT). If resistance at 100 °C is 139 Ω, at 0 °C is 100 Ω, then temperature coefficient α is:
🔵 (A) 0.0039 /°C
🟢 (B) 0.0040 /°C
🟠 (C) 0.0020 /°C
🔴 (D) 0.0010 /°C
Answer: (B) 0.0040 /°C
Year: 2024 | Shift 2 | Set Q | JEE Main
Q5.
In a meter bridge experiment, a resistance of 6 Ω is balanced at 40 cm. The unknown resistance is:
🔵 (A) 4 Ω
🟢 (B) 6 Ω
🟠 (C) 9 Ω
🔴 (D) 10 Ω
Answer: (A) 4 Ω
Year: 2024 | Shift 1 | Set R | JEE Main
Q6.
When a current flows through a conductor, the drift velocity of electrons is of the order of:
🔵 (A) 10² m/s
🟢 (B) 10⁻⁷ m/s
🟠 (C) 10⁻⁴ m/s
🔴 (D) 10⁻¹ m/s
Answer: (C) 10⁻⁴ m/s
Year: 2024 | Shift 2 | Set S | JEE Main
Q7.
Two cells of emf 2 V and 1.5 V with internal resistances 0.5 Ω and 0.25 Ω respectively are connected in parallel. The effective emf is:
🔵 (A) 1.75 V
🟢 (B) 2.0 V
🟠 (C) 1.0 V
🔴 (D) 3.5 V
Answer: (A) 1.75 V
Year: 2023 | Shift 1 | Set T | JEE Main
Q8.
A wire of resistance 10 Ω is stretched to three times its length. Its new resistance is:
🔵 (A) 30 Ω
🟢 (B) 90 Ω
🟠 (C) 100 Ω
🔴 (D) 300 Ω
Answer: (B) 90 Ω
Year: 2023 | Shift 2 | Set U | JEE Main
Q9.
A copper wire of cross-sectional area 1 mm² carries a current of 3 A. If number density of electrons is 8.5 × 10²⁸ m⁻³, the drift velocity is approximately:
🔵 (A) 2 × 10⁻³ m/s
🟢 (B) 2 × 10⁻⁴ m/s
🟠 (C) 2 × 10⁻⁵ m/s
🔴 (D) 2 × 10⁻⁶ m/s
Answer: (C) 2 × 10⁻⁵ m/s
Year: 2023 | Shift 2 | Set V | JEE Main
Q10.
The sensitivity of potentiometer increases by:
🔵 (A) increasing length of wire
🟢 (B) decreasing length of wire
🟠 (C) increasing current through wire
🔴 (D) increasing cross-sectional area of wire
Answer: (A) Increasing length of wire
Year: 2022 | Shift 1 | Set W | JEE Main
Q11.
The resistance of a conductor at 0 °C is 10 Ω. At 100 °C, its resistance is 15 Ω. The temperature coefficient of resistance is:
🔵 (A) 0.005 /°C
🟢 (B) 0.004 /°C
🟠 (C) 0.003 /°C
🔴 (D) 0.002 /°C
Answer: (B) 0.004 /°C
Year: 2022 | Shift 2 | Set X | JEE Main
Q12.
A potentiometer wire of length 100 cm and resistance 10 Ω is connected across a 2 V battery. The potential gradient is:
🔵 (A) 0.002 V/cm
🟢 (B) 0.02 V/cm
🟠 (C) 0.2 V/cm
🔴 (D) 2 V/cm
Answer: (B) 0.02 V/cm
Year: 2021 | Shift 1 | Set Y | JEE Main
Q13.
If the length of a wire is doubled and radius halved, its resistance becomes:
🔵 (A) 4R
🟢 (B) 8R
🟠 (C) 16R
🔴 (D) R/2
Answer: (B) 8R
Year: 2021 | Shift 2 | Set Z | JEE Main
Q14.
The internal resistance of a cell is r. To get maximum power from the cell, the external resistance should be:
🔵 (A) r/2
🟢 (B) r
🟠 (C) 2r
🔴 (D) ∞
Answer: (B) r
Year: 2020 | Shift 1 | Set A | JEE Main
Q15.
The drift velocity of electrons in a wire is 2 × 10⁻⁴ m/s. If number density of electrons is doubled, then for same current the drift velocity becomes:
🔵 (A) 4 × 10⁻⁴ m/s
🟢 (B) 1 × 10⁻⁴ m/s
🟠 (C) 2 × 10⁻⁴ m/s
🔴 (D) 8 × 10⁻⁴ m/s
Answer: (B) 1 × 10⁻⁴ m/s
Year: 2020 | Shift 2 | Set B | JEE Main
Q16.
Two wires of same material and length have resistances 4 Ω and 9 Ω. The ratio of their radii is:
🔵 (A) 2:3
🟢 (B) 3:2
🟠 (C) 4:9
🔴 (D) 9:4
Answer: (A) 2:3
Year: 2019 | Shift 1 | Set C | JEE Main
Q17.
In a potentiometer, balancing length for emf E₁ is 120 cm and for E₂ is 180 cm. The ratio E₁/E₂ is:
🔵 (A) 1/2
🟢 (B) 2/3
🟠 (C) 2/1
🔴 (D) 3/2
Answer: (B) 2/3
Year: 2019 | Shift 2 | Set D | JEE Main
Q18.
If 1 A current flows through a wire of cross-section 1 mm², the drift velocity is of the order of:
🔵 (A) 10⁻⁶ m/s
🟢 (B) 10⁻⁴ m/s
🟠 (C) 10⁻² m/s
🔴 (D) 1 m/s
Answer: (A) 10⁻⁶ m/s
Year: 2019 | Shift 2 | Set E | JEE Main
Q19.
The effective resistance between A and B of two resistors of 2 Ω and 6 Ω connected in parallel is:
🔵 (A) 3 Ω
🟢 (B) 2 Ω
🟠 (C) 1.5 Ω
🔴 (D) 4 Ω
Answer: (C) 1.5 Ω
Year: 2018 | Shift 1 | Set F | JEE Main
Q20.
Ohm’s law fails for:
🔵 (A) Copper
🟢 (B) Nichrome
🟠 (C) Vacuum tubes
🔴 (D) Manganin
Answer: (C) Vacuum tubes
Year: 2018 | Shift 2 | Set G | JEE Main
Q21.
The efficiency of a cell is maximum when external resistance is:
🔵 (A) equal to internal resistance
🟢 (B) much larger than internal resistance
🟠 (C) much smaller than internal resistance
🔴 (D) zero
Answer: (A) Equal to internal resistance
Year: 2017 | Shift 1 | Set H | JEE Main
Q22.
A wire of resistance R is stretched to n times its length. Its new resistance will be:
🔵 (A) R/n
🟢 (B) nR
🟠 (C) n²R
🔴 (D) R/n²
Answer: (C) n²R
Year: 2017 | Shift 2 | Set I | JEE Main
Q23.
In a Wheatstone bridge, four resistors of 10 Ω each are connected. The resistance of the galvanometer arm is:
🔵 (A) Infinite
🟢 (B) Zero
🟠 (C) 10 Ω
🔴 (D) 5 Ω
Answer: (B) Zero
Year: 2016 | Shift 1 | Set J | JEE Main
Q24.
In a potentiometer, emf of a cell is measured to avoid:
🔵 (A) internal resistance effect
🟢 (B) external resistance effect
🟠 (C) heating effect
🔴 (D) current variation
Answer: (A) Internal resistance effect
Year: 2016 | Shift 2 | Set K | JEE Main
Q25.
If current of 2 A flows through a conductor for 2 s, the charge passing is:
🔵 (A) 2 C
🟢 (B) 4 C
🟠 (C) 1 C
🔴 (D) 0.5 C
Answer: (B) 4 C
Year: 2015 | Single Sitting | Code L | JEE Main
Q26.
A 2 V cell is connected across a 6 Ω resistor. The power dissipated is:
🔵 (A) 0.25 W
🟢 (B) 0.67 W
🟠 (C) 2 W
🔴 (D) 6 W
Answer: (B) 0.67 W
Year: 2015 | Single Sitting | Code M | JEE Main
Q27.
The resistance of a wire at 20 °C is 20 Ω. If temperature coefficient is 0.004/°C, the resistance at 120 °C is:
🔵 (A) 28 Ω
🟢 (B) 24 Ω
🟠 (C) 32 Ω
🔴 (D) 36 Ω
Answer: (A) 28 Ω
Year: 2014 | Single Sitting | Code N | JEE Main
Q28.
The drift velocity of electrons in a copper wire of cross-sectional area 1 mm² carrying current of 3 A is approximately:
🔵 (A) 2 × 10⁻⁶ m/s
🟢 (B) 2 × 10⁻⁴ m/s
🟠 (C) 2 × 10⁻³ m/s
🔴 (D) 2 × 10⁻² m/s
Answer: (A) 2 × 10⁻⁶ m/s
Year: 2014 | Single Sitting | Code O | JEE Main
Q29.
The resistance of a conductor does not depend on:
🔵 (A) length
🟢 (B) material
🟠 (C) temperature
🔴 (D) current passing
Answer: (D) Current passing
Year: 2013 | Single Sitting | Code P | JEE Main
Q30.
Two wires of same material, one twice length and double diameter of other. Their resistances are in ratio:
🔵 (A) 1:1
🟢 (B) 1:2
🟠 (C) 1:4
🔴 (D) 1:8
Answer: (C) 1:4
Year: 2013 | Single Sitting | Code Q | JEE Main
Q31.
The equivalent resistance of two resistors 2 Ω and 6 Ω connected in parallel is:
🔵 (A) 8 Ω
🟢 (B) 3 Ω
🟠 (C) 1.5 Ω
🔴 (D) 12 Ω
Answer: (C) 1.5 Ω
Year: 2012 | Single Sitting | Code R | AIEEE
Q32.
The resistance of a copper wire is 10 Ω at 0 °C and 11 Ω at 100 °C. The temperature coefficient is:
🔵 (A) 0.001 /°C
🟢 (B) 0.002 /°C
🟠 (C) 0.003 /°C
🔴 (D) 0.004 /°C
Answer: (A) 0.001 /°C
Year: 2012 | Single Sitting | Code S | AIEEE
Q33.
A galvanometer of resistance 10 Ω is converted to a voltmeter of range 50 V by connecting a resistance of 990 Ω in series. The resistance of galvanometer is:
🔵 (A) 1000 Ω
🟢 (B) 10 Ω
🟠 (C) 20 Ω
🔴 (D) 50 Ω
Answer: (B) 10 Ω
Year: 2011 | Single Sitting | Code T | AIEEE
Q34.
When a wire is stretched to double its length, the resistance becomes:
🔵 (A) R
🟢 (B) 2R
🟠 (C) 3R
🔴 (D) 4R
Answer: (D) 4R
Year: 2011 | Single Sitting | Code U | AIEEE
Q35.
If n is the number density of electrons, e is electronic charge, A is area, I is current, then drift velocity is:
🔵 (A) I/An
🟢 (B) I/nae
🟠 (C) ne/IA
🔴 (D) A/Ine
Answer: (B) I/nae
Year: 2010 | Single Sitting | Code V | AIEEE
Q36.
The resistance of a conductor at 0 °C is 5 Ω. If temperature coefficient is 0.004/°C, its resistance at 100 °C is:
🔵 (A) 6 Ω
🟢 (B) 7 Ω
🟠 (C) 9 Ω
🔴 (D) 10 Ω
Answer: (B) 7 Ω
Year: 2010 | Single Sitting | Code W | AIEEE
Q37.
In a potentiometer experiment, balancing length is found to be 50 cm for a cell of emf 2 V. The potential gradient is:
🔵 (A) 0.02 V/cm
🟢 (B) 0.04 V/cm
🟠 (C) 0.03 V/cm
🔴 (D) 0.01 V/cm
Answer: (B) 0.04 V/cm
Year: 2009 | Single Sitting | Code X | AIEEE
Q38.
The resistance of a wire is R. Its length is doubled and diameter also doubled. The
ChatGPT said:
new resistance is:
🔵 (A) R
🟢 (B) R/2
🟠 (C) 2R
🔴 (D) R/4
Answer: (B) R/2
Year: 2009 | Single Sitting | Code Y | AIEEE
Q39.
The specific resistance of a conductor depends on:
🔵 (A) length only
🟢 (B) cross-section only
🟠 (C) material only
🔴 (D) both length and area
Answer: (C) Material only
Year: 2008 | Single Sitting | Code Z | AIEEE
Q40.
The current through a wire depends on drift velocity and number of electrons per unit volume as:
🔵 (A) I = neAvd
🟢 (B) I = nAvd
🟠 (C) I = vd/nae
🔴 (D) I = neA/vd
Answer: (A) I = neAvd
Year: 2008 | Single Sitting | Code A1 | AIEEE
Q41.
The resistivity of a metal conductor increases with:
🔵 (A) decrease in temperature
🟢 (B) increase in temperature
🟠 (C) decrease in mass
🔴 (D) none of these
Answer: (B) Increase in temperature
Year: 2007 | Single Sitting | Code B1 | AIEEE
Q42.
A cell of emf 2 V and internal resistance 0.1 Ω is connected to a 3.9 Ω external resistance. The current is:
🔵 (A) 0.5 A
🟢 (B) 0.25 A
🟠 (C) 2 A
🔴 (D) 1 A
Answer: (A) 0.5 A
Year: 2007 | Single Sitting | Code C1 | AIEEE
Q43.
The reciprocal of resistance is called:
🔵 (A) Reactance
🟢 (B) Conductivity
🟠 (C) Resistivity
🔴 (D) Conductance
Answer: (D) Conductance
Year: 2006 | Single Sitting | Code D1 | AIEEE
Q44.
The unit of resistivity is:
🔵 (A) Ω
🟢 (B) Ω·m
🟠 (C) Ω/m
🔴 (D) Ω·m²
Answer: (B) Ω·m
Year: 2006 | Single Sitting | Code E1 | AIEEE
Q45.
Two wires of same length and material have resistances R and 4R. Their radii are in ratio:
🔵 (A) 1:2
🟢 (B) 2:1
🟠 (C) 1:4
🔴 (D) 4:1
Answer: (A) 1:2
Year: 2005 | Single Sitting | Code F1 | AIEEE
Q46.
The drift velocity of electrons in a conductor is inversely proportional to:
🔵 (A) charge on electron
🟢 (B) relaxation time
🟠 (C) number density
🔴 (D) electric field
Answer: (C) Number density
Year: 2005 | Single Sitting | Code G1 | AIEEE
Q47.
In a conductor, Ohm’s law is obeyed when:
🔵 (A) temperature constant
🟢 (B) pressure constant
🟠 (C) current constant
🔴 (D) potential constant
Answer: (A) Temperature constant
Year: 2004 | Single Sitting | Code H1 | AIEEE
Q48.
A copper wire of resistance 20 Ω is drawn to half its length and same volume. The new resistance is:
🔵 (A) 20 Ω
🟢 (B) 5 Ω
🟠 (C) 10 Ω
🔴 (D) 40 Ω
Answer: (B) 5 Ω
Year: 2004 | Single Sitting | Code I1 | AIEEE
Q49.
The dimensional formula of resistivity is:
🔵 (A) ML²T⁻³A⁻²
🟢 (B) ML³T⁻³A⁻²
🟠 (C) ML²T⁻²A⁻²
🔴 (D) ML⁻¹T³A²
Answer: (A) ML²T⁻³A⁻²
Year: 2003 | Single Sitting | Code J1 | AIEEE
Q50.
In a potentiometer experiment, balancing length is proportional to:
🔵 (A) square of emf
🟢 (B) emf of cell
🟠 (C) resistance of wire
🔴 (D) current through wire
Answer: (B) Emf of cell
Year: 2002 | Single Sitting | Code K1 | AIEEE
————————————————————————————————————————————————————————————————————————————
JEE ADVANCED QUESTIONS FROM THIS LESSON
Paper 1 (Q1–Q17)
Q1. A uniform wire of resistance 9 Ω is cut into three equal parts and connected in parallel. The equivalent resistance is:
🔵 (A) 1 Ω
🟢 (B) 3 Ω
🟠 (C) 9 Ω
🔴 (D) 27 Ω
Answer: (A) 1 Ω
Year: 2025 | Paper 1 | Set 1
Q2. A potentiometer wire of length L and resistance R is connected to a cell of emf E. The potential gradient is:
🔵 (A) E/L
🟢 (B) EL/R
🟠 (C) E/RL
🔴 (D) ER/L
Answer: (A) E/L
Year: 2025 | Paper 1 | Set 2
Q3. A copper wire is stretched to double its length. The resistivity of the wire:
🔵 (A) doubles
🟢 (B) halves
🟠 (C) remains unchanged
🔴 (D) becomes four times
Answer: (C) Remains unchanged
Year: 2024 | Paper 1 | Code P
Q4. In a meter bridge, the balancing length is 40 cm. If the known resistance is 6 Ω, the unknown resistance is:
🔵 (A) 4 Ω
🟢 (B) 9 Ω
🟠 (C) 10 Ω
🔴 (D) 12 Ω
Answer: (A) 4 Ω
Year: 2024 | Paper 1 | Code Q
Q5. For a metal, the relation between resistivity (ρ) and temperature (T) is approximately:
🔵 (A) ρ ∝ 1/T
🟢 (B) ρ ∝ √T
🟠 (C) ρ ∝ T
🔴 (D) ρ ∝ T²
Answer: (C) ρ ∝ T
Year: 2023 | Paper 1 | Code P
Q6. Two wires of equal length and same material have resistances 4 Ω and 9 Ω. The ratio of their radii is:
🔵 (A) 2:3
🟢 (B) 3:2
🟠 (C) 4:9
🔴 (D) 9:4
Answer: (A) 2:3
Year: 2023 | Paper 1 | Code Q
Q7. A cell of emf 2 V and internal resistance 0.5 Ω is connected to an external resistance of 3.5 Ω. The current in the circuit is:
🔵 (A) 0.25 A
🟢 (B) 0.5 A
🟠 (C) 1 A
🔴 (D) 2 A
Answer: (B) 0.5 A
Year: 2022 | Paper 1 | Code P
Q8. Drift velocity is proportional to:
🔵 (A) Current density
🟢 (B) Square of current density
🟠 (C) 1/Current density
🔴 (D) 1/(Current density)²
Answer: (A) Current density
Year: 2022 | Paper 1 | Code Q
Q9. A potentiometer measures emf more accurately than a voltmeter because:
🔵 (A) it does not draw current from source
🟢 (B) it has very high resistance
🟠 (C) it has very low resistance
🔴 (D) it is cheap and portable
Answer: (A) It does not draw current from source
Year: 2021 | Paper 1 | Code P
Q10. The reciprocal of resistance is:
🔵 (A) Conductance
🟢 (B) Resistivity
🟠 (C) Reactance
🔴 (D) Inductance
Answer: (A) Conductance
Year: 2021 | Paper 1 | Code Q
Q11. A resistance of 10 Ω is connected across a battery of emf 2 V with negligible internal resistance. The current is:
🔵 (A) 0.1 A
🟢 (B) 0.2 A
🟠 (C) 0.5 A
🔴 (D) 2 A
Answer: (B) 0.2 A
Year: 2020 | Paper 1 | Code P
Q12. In a Wheatstone bridge, the four resistances are equal. The galvanometer shows:
🔵 (A) Maximum deflection
🟢 (B) No deflection
🟠 (C) Half deflection
🔴 (D) Random deflection
Answer: (B) No deflection
Year: 2020 | Paper 1 | Code Q
Q13. The drift velocity of electrons depends on:
🔵 (A) electron mass
🟢 (B) number density of electrons
🟠 (C) relaxation time
🔴 (D) all of these
Answer: (D) All of these
Year: 2019 | Paper 1 | Code P
Q14. A wire of resistance R is stretched to double its length. The new resistance is:
🔵 (A) R
🟢 (B) 2R
🟠 (C) 3R
🔴 (D) 4R
Answer: (D) 4R
Year: 2019 | Paper 1 | Code Q
Q15. A material that obeys Ohm’s law is called:
🔵 (A) non-ohmic
🟢 (B) ohmic
🟠 (C) dielectric
🔴 (D) insulator
Answer: (B) Ohmic
Year: 2018 | Paper 1 | Code P
Q16. The SI unit of resistivity is:
🔵 (A) Ω
🟢 (B) Ω·m
🟠 (C) Ω/m
🔴 (D) Ω·m²
Answer: (B) Ω·m
Year: 2018 | Paper 1 | Code Q
Q17. Current in a metallic conductor is due to:
🔵 (A) protons
🟢 (B) free electrons
🟠 (C) neutrons
🔴 (D) holes
Answer: (B) Free electrons
Year: 2017 | Paper 1 | Code P
Paper 2 (Q18–Q34)
Q18. A 10 V battery with internal resistance 1 Ω is connected to a 9 Ω resistor. The current is:
🔵 (A) 0.5 A
🟢 (B) 1 A
🟠 (C) 1.5 A
🔴 (D) 9 A
Answer: (B) 1 A
Year: 2025 | Paper 2 | Set 1
Q19. The drift velocity of electrons in a copper wire carrying 3 A current is of order:
🔵 (A) 10⁻⁶ m/s
🟢 (B) 10⁻³ m/s
🟠 (C) 10⁻² m/s
🔴 (D) 10 m/s
Answer: (A) 10⁻⁶ m/s
Year: 2025 | Paper 2 | Set 2
Q20. If current is doubled in a conductor, the drift velocity is:
🔵 (A) halved
🟢 (B) doubled
🟠 (C) unchanged
🔴 (D) four times
Answer: (B) Doubled
Year: 2024 | Paper 2 | Code P
Q21. A potentiometer balances a cell of emf 2 V at length 100 cm. The potential gradient is:
🔵 (A) 0.02 V/cm
🟢 (B) 0.2 V/cm
🟠 (C) 2 V/cm
🔴 (D) 0.002 V/cm
Answer: (A) 0.02 V/cm
Year: 2024 | Paper 2 | Code Q
Q22. The internal resistance of a cell can be measured using:
🔵 (A) Voltmeter
🟢 (B) Potentiometer
🟠 (C) Ammeter
🔴 (D) Galvanometer
Answer: (B) Potentiometer
Year: 2023 | Paper 2 | Code P
Q23. Resistivity of a metal depends on:
🔵 (A) material and temperature
🟢 (B) length of conductor
🟠 (C) cross-sectional area
🔴 (D) applied potential
Answer: (A) Material and temperature
Year: 2023 | Paper 2 | Code Q
Q24. In a conductor, drift velocity vd is proportional to:
🔵 (A) Electric field
🟢 (B) Square of electric field
🟠 (C) 1/E
🔴 (D) Independent of E
Answer: (A) Electric field
Year: 2022 | Paper 2 | Code P
Q25. A 12 V battery is connected to a 6 Ω resistor. The current in the circuit is:
🔵 (A) 1 A
🟢 (B) 2 A
🟠 (C) 0.5 A
🔴 (D) 3 A
Answer: (B) 2 A
Year: 2022 | Paper 2 | Code Q
Q26. Resistance of a wire increases with:
🔵 (A) decrease in length
🟢 (B) increase in length
🟠 (C) decrease in resistivity
🔴 (D) decrease in temperature
Answer: (B) Increase in length
Year: 2021 | Paper 2 | Code P
Q27. A wire of length L and radius r has resistance R. Its resistivity is proportional to:
🔵 (A) RL/πr²
🟢 (B) Rπr²/L
🟠 (C) RL/πr
🔴 (D) R/r²L
Answer: (B) Rπr²/L
Year: 2021 | Paper 2 | Code Q
Q28. The condition for Wheatstone bridge balance is:
🔵 (A) P/Q = R/S
🟢 (B) P/Q = S/R
🟠 (C) PQ = RS
🔴 (D) P+Q = R+S
Answer: (A) P/Q = R/S
Year: 2020 | Paper 2 | Code P
Q29. Resistivity is expressed in units:
🔵 (A) Ω
🟢 (B) Ω·m
🟠 (C) Ω/m
🔴 (D) Ω·m²
Answer: (B) Ω·m
Year: 2020 | Paper 2 | Code Q
Q30. A cell is used to drive 0.5 A through a 4 Ω resistor. The emf of the cell is (neglecting internal resistance):
🔵 (A) 1 V
🟢 (B) 2 V
🟠 (C) 4 V
🔴 (D) 8 V
Answer: (B) 2 V
Year: 2019 | Paper 2 | Code P
Q31. If the radius of a conductor is doubled, its resistance becomes:
🔵 (A) Half
🟢 (B) One-fourth
🟠 (C) Double
🔴 (D) Four times
Answer: (B) One-fourth
Year: 2019 | Paper 2 | Code Q
Q32. The SI unit of conductivity is:
🔵 (A) Ω·m
🟢 (B) Ω⁻¹·m⁻¹
🟠 (C) Ω/m
🔴 (D) Ω·m²
Answer: (B) Ω⁻¹·m⁻¹
Year: 2018 | Paper 2 | Code P
Q33. A material which does not obey Ohm’s law is:
🔵 (A) Manganin
🟢 (B) Nichrome
🟠 (C) Semiconductor diode
🔴 (D) Copper
Answer: (C) Semiconductor diode
Year: 2018 | Paper 2 | Code Q
Q34. In a potentiometer experiment, balancing length is directly proportional to:
🔵 (A) emf of cell
🟢 (B) resistance of wire
🟠 (C) current through wire
🔴 (D) cross-sectional area of wire
Answer: (A) emf of cell
Year: 2017 | Paper 2 | Code P
———————————————————————————————————————————————————————————————————————————-
PRACTICE SETS FROM THIS LESSON
NEET Level (Q1–Q20)
Q1. The SI unit of resistivity is:
🔵 (A) Ω
🟢 (B) Ω·m
🟠 (C) Ω/m
🔴 (D) Ω·m²
Answer: (B) Ω·m
Q2. Drift velocity of electrons in a conductor is of order:
🔵 (A) 10² m/s
🟢 (B) 10⁻² m/s
🟠 (C) 10⁻⁴ m/s
🔴 (D) 10⁶ m/s
Answer: (C) 10⁻⁴ m/s
Q3. Which quantity does not depend on drift velocity?
🔵 (A) Current density
🟢 (B) Current
🟠 (C) Resistance
🔴 (D) Conductivity
Answer: (C) Resistance
Q4. The resistance of a wire depends on:
🔵 (A) length and area of cross-section
🟢 (B) material
🟠 (C) temperature
🔴 (D) All of these
Answer: (D) All of these
Q5. A cell of emf 2 V and internal resistance 0.5 Ω supplies current to 9.5 Ω external resistance. The current is:
🔵 (A) 0.1 A
🟢 (B) 0.2 A
🟠 (C) 0.5 A
🔴 (D) 2 A
Answer: (C) 0.5 A
Q6. The reciprocal of resistance is called:
🔵 (A) Conductivity
🟢 (B) Conductance
🟠 (C) Resistivity
🔴 (D) Reactance
Answer: (B) Conductance
Q7. In a Wheatstone bridge, if all four resistors are equal, the galvanometer shows:
🔵 (A) No deflection
🟢 (B) Maximum deflection
🟠 (C) Half deflection
🔴 (D) Random deflection
Answer: (A) No deflection
Q8. Which of the following is an ohmic conductor?
🔵 (A) Copper
🟢 (B) Silicon
🟠 (C) Diode
🔴 (D) Transistor
Answer: (A) Copper
Q9. The temperature coefficient of resistance of a conductor is positive. This means:
🔵 (A) Resistance decreases with rise of temperature
🟢 (B) Resistance increases with rise of temperature
🟠 (C) Resistance is independent of temperature
🔴 (D) Conductivity increases with temperature
Answer: (B) Resistance increases with rise of temperature
Q10. Potential gradient in a potentiometer wire is:
🔵 (A) Potential difference / Current
🟢 (B) Emf / Resistance
🟠 (C) Potential difference / Length
🔴 (D) Current / Area
Answer: (C) Potential difference / Length
Q11. Which instrument measures emf of a cell without drawing current?
🔵 (A) Voltmeter
🟢 (B) Potentiometer
🟠 (C) Ammeter
🔴 (D) Galvanometer
Answer: (B) Potentiometer
Q12. If length of a wire is doubled keeping volume constant, resistance becomes:
🔵 (A) R
🟢 (B) 2R
🟠 (C) 4R
🔴 (D) R/2
Answer: (C) 4R
Q13. The resistivity of a wire depends on:
🔵 (A) Length
🟢 (B) Cross-sectional area
🟠 (C) Temperature and material
🔴 (D) None of these
Answer: (C) Temperature and material
Q14. In series combination of resistors:
🔵 (A) Same current flows
🟢 (B) Same voltage across each
🟠 (C) Reciprocal of resistances add
🔴 (D) Power remains same
Answer: (A) Same current flows
Q15. In parallel combination of resistors:
🔵 (A) Current divides
🟢 (B) Voltage divides
🟠 (C) Resistance increases
🔴 (D) Current same in all
Answer: (A) Current divides
Q16. A wire has resistance R. If its length is doubled and radius halved, new resistance is:
🔵 (A) 2R
🟢 (B) 4R
🟠 (C) 8R
🔴 (D) 16R
Answer: (C) 8R
Q17. The unit of conductivity is:
🔵 (A) Ω·m
🟢 (B) Ω⁻¹·m⁻¹
🟠 (C) Ω·m²
🔴 (D) Ω/m
Answer: (B) Ω⁻¹·m⁻¹
Q18. Kirchhoff’s first law (junction rule) is based on conservation of:
🔵 (A) Energy
🟢 (B) Charge
🟠 (C) Momentum
🔴 (D) Mass
Answer: (B) Charge
Q19. Kirchhoff’s second law (loop rule) is based on conservation of:
🔵 (A) Energy
🟢 (B) Charge
🟠 (C) Momentum
🔴 (D) Mass
Answer: (A) Energy
Q20. The slope of V–I graph for an ohmic conductor represents:
🔵 (A) Resistance
🟢 (B) Conductance
🟠 (C) Power
🔴 (D) Current density
Answer: (A) Resistance
JEE Main Level (Q21–Q40)
Q21. A wire of resistance R is cut into n equal parts and all are connected in parallel. The equivalent resistance is:
🔵 (A) R/n
🟢 (B) R/n²
🟠 (C) nR
🔴 (D) R²/n
Answer: (B) R/n²
Q22. A potentiometer is preferred over a voltmeter to measure emf because:
🔵 (A) It is cheaper
🟢 (B) It does not draw current from cell
🟠 (C) It is portable
🔴 (D) It has low resistance
Answer: (B) It does not draw current from cell
Q23. Current density J is related to conductivity σ and electric field E as:
🔵 (A) J = σE
🟢 (B) J = E/σ
🟠 (C) J = σ/E
🔴 (D) J = 1/σE
Answer: (A) J = σE
Q24. A conductor of length L and cross-sectional area A has resistance R. If both L and A are doubled, the new resistance is:
🔵 (A) R
🟢 (B) R/2
🟠 (C) 2R
🔴 (D) 4R
Answer: (B) R/2
Q25. In a circuit, two resistors 4 Ω and 6 Ω are connected in series across a 10 V battery. The current is:
🔵 (A) 1 A
🟢 (B) 2 A
🟠 (C) 0.5 A
🔴 (D) 5 A
Answer: (A) 1 A
Q26. Two resistances of 12 Ω and 18 Ω are connected in parallel. Their effective resistance is:
🔵 (A) 6 Ω
🟢 (B) 10 Ω
🟠 (C) 12 Ω
🔴 (D) 30 Ω
Answer: (A) 6 Ω
Q27. A wire of resistance 20 Ω is drawn such that its length becomes double and volume remains constant. The new resistance is:
🔵 (A) 40 Ω
🟢 (B) 80 Ω
🟠 (C) 60 Ω
🔴 (D) 100 Ω
Answer: (B) 80 Ω
Q28. The drift velocity is directly proportional to:
🔵 (A) Current
🟢 (B) Resistivity
🟠 (C) Cross-sectional area
🔴 (D) Length of conductor
Answer: (A) Current
Q29. The current through a wire depends on:
🔵 (A) Cross-sectional area
🟢 (B) Number density of electrons
🟠 (C) Drift velocity
🔴 (D) All of these
Answer: (D) All of these
Q30. A battery of emf 6 V and internal resistance 1 Ω is connected to a 5 Ω external resistance. The current is:
🔵 (A) 1 A
🟢 (B) 1.2 A
🟠 (C) 1.5 A
🔴 (D) 6 A
Answer: (B) 1.2 A
Q31. The effective resistance of three resistors 3 Ω, 6 Ω, and 9 Ω connected in parallel is:
🔵 (A) 2 Ω
🟢 (B) 3 Ω
🟠 (C) 4.5 Ω
🔴 (D) 6 Ω
Answer: (A) 2 Ω
Q32. Which of the following combinations gives maximum resistance?
🔵 (A) All resistors in series
🟢 (B) All resistors in parallel
🟠 (C) Mixed series-parallel
🔴 (D) Depends on resistance values
Answer: (A) All resistors in series
Q33. A current of 3 A flows through a conductor for 2 s. The charge passed is:
🔵 (A) 1.5 C
🟢 (B) 6 C
🟠 (C) 3 C
🔴 (D) 0.5 C
Answer: (B) 6 C
Q34. In a meter bridge, if the balancing length is 60 cm, then resistance ratio R₁/R₂ is:
🔵 (A) 60/40
🟢 (B) 40/60
🟠 (C) 60/100
🔴 (D) 100/40
Answer: (A) 60/40
Q35. The resistance of a conductor increases with:
🔵 (A) decrease in temperature
🟢 (B) increase in temperature
🟠 (C) decrease in length
🔴 (D) increase in area
Answer: (B) Increase in temperature
Q36. The heating effect of current is governed by:
🔵 (A) P = VI
🟢 (B) P = I²R
🟠 (C) P = V²/R
🔴 (D) All of these
Answer: (D) All of these
Q37. If cross-sectional area of a wire is doubled, its resistance becomes:
🔵 (A) R
🟢 (B) R/2
🟠 (C) 2R
🔴 (D) 4R
Answer: (B) R/2
Q38. Resistivity of a semiconductor:
🔵 (A) Increases with temperature
🟢 (B) Decreases with temperature
🟠 (C) Remains constant
🔴 (D) Is infinite
Answer: (B) Decreases with temperature
Q39. In potentiometer experiment, if current in wire increases, potential gradient:
🔵 (A) Increases
🟢 (B) Decreases
🟠 (C) Remains same
🔴 (D) Becomes zero
Answer: (A) Increases
Q40. A voltmeter of resistance 200 Ω is connected across 800 Ω resistor. Effective resistance of combination is:
🔵 (A) 1000 Ω
🟢 (B) 160 Ω
🟠 (C) 600 Ω
🔴 (D) 200 Ω
Answer: (B) 160 Ω
JEE Advanced Level (Q41–Q50)
Q41. A 1 m wire has resistance 4 Ω. It is bent into a circle. The effective resistance between two diametrically opposite points is:
🔵 (A) 4 Ω
🟢 (B) 2 Ω
🟠 (C) 1 Ω
🔴 (D) 0.5 Ω
Answer: (B) 2 Ω
Q42. A 100 W bulb rated at 200 V is connected across 100 V. The power consumed is:
🔵 (A) 25 W
🟢 (B) 50 W
🟠 (C) 100 W
🔴 (D) 200 W
Answer: (A) 25 W
Q43. A conductor of resistance 12 Ω is cut into 3 equal pieces and connected in series. Equivalent resistance is:
🔵 (A) 36 Ω
🟢 (B) 12 Ω
🟠 (C) 4 Ω
🔴 (D) 6 Ω
Answer: (A) 36 Ω
Q44. Two cells of emf 1.5 V and 2 V, internal resistances 1 Ω and 2 Ω respectively, are connected in parallel. Their equivalent emf is:
🔵 (A) 1.6 V
🟢 (B) 1.7 V
🟠 (C) 2 V
🔴 (D) 3.5 V
Answer: (B) 1.7 V
Q45. A wire of resistance 10 Ω is stretched to 1.5 times length. Its resistance becomes:
🔵 (A) 10 Ω
🟢 (B) 15 Ω
🟠 (C) 22.5 Ω
🔴 (D) 25 Ω
Answer: (C) 22.5 Ω
Q46. Drift velocity of electrons is inversely proportional to:
🔵 (A) Current density
🟢 (B) Cross-sectional area
🟠 (C) Number density of electrons
🔴 (D) Electron charge
Answer: (C) Number density of electrons
Q47. In a potentiometer experiment, balancing length for a cell of emf 1.5 V is 75 cm. For a cell of emf 3 V, balancing length is:
🔵 (A) 75 cm
🟢 (B) 150 cm
🟠 (C) 37.5 cm
🔴 (D) 100 cm
Answer: (B) 150 cm
Q48. A battery of emf 3 V and internal resistance 1 Ω is connected to 5 Ω resistor. Efficiency is:
🔵 (A) 60%
🟢 (B) 80%
🟠 (C) 50%
🔴 (D) 75%
Answer: (B) 80%
Q49. In a conductor, relaxation time increases. Its conductivity will:
🔵 (A) Decrease
🟢 (B) Increase
🟠 (C) Remain constant
🔴 (D) Become infinite
Answer: (B) Increase
Q50. A potentiometer wire of length 100 cm is connected to a battery. If potential drop per cm is 0.01 V, balancing length required for a cell of emf 1 V is:
🔵 (A) 150 cm
🟢 (B) 100 cm
🟠 (C) 50 cm
🔴 (D) 75 cm
Answer: (B) 100 cm
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MIND MAP
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