Electric Current (Drift Velocity, Mobility and their Relation with Electric Current) NEET Questions

Physics - Current Electricity
Electric Current (Drift Velocity, Mobility and their Relation with Electric Current)

Electric Current (Drift Velocity, Mobility and their Relation with Electric Current) MCQ Questions


13.
A current of 4.8 A is flowing in a copper wire of cross-sectional area 3 × 10⁻⁴ m². If the free electron density in copper is 10²⁹ m⁻³, the drift velocity of electrons is:
A.
1 × 10⁻⁴ m/s
B.
1 × 10⁻³ m/s
C.
1 × 10⁻⁶ m/s
D.
1 × 10⁻⁵ m/s
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ANSWER :
C. 1 × 10⁻⁶ m/s
14.
The drift velocity of electrons in a wire of radius r is v_d. If both the current and radius are doubled, then the drift velocity becomes:
A.
v_d
B.
v_d/2
C.
4v_d
D.
2v_d
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ANSWER :
B. v_d/2
15.
Two wires A and B of same material and same length but radii in ratio 1:2 are connected in series. The ratio of drift velocities of electrons in A and B is:
A.
1:2
B.
4:1
C.
1:1
D.
2:1
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ANSWER :
B. 4:1
16.
Two wires of same material and same length but different cross-sectional areas A₁ and A₂ are joined in parallel across a battery. The ratio of drift velocities of electrons in them is:
A.
A₁²:A₂²
B.
1:1
C.
A₂:A₁
D.
A₁:A₂
😑 View Answer Error
ANSWER :
B. 1:1
17.
The relaxation time τ of free electrons in a metal having resistivity ρ, mass m, charge e and number density n is:
A.
ne²ρ/m
B.
ne/(mρ)
C.
mρ/(ne²)
D.
m/(ne²ρ)
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ANSWER :
D. m/(ne²ρ)
18.
The current density at a point in a conductor is 5 A/m². If the number density of free electrons is 8 × 10²⁸ m⁻³, the drift velocity is:
A.
6.25 × 10¹⁸ m/s
B.
3.9 × 10⁻⁸ m/s
C.
1.6 × 10⁻¹⁹ m/s
D.
3.9 × 10⁻¹⁰ m/s
😑 View Answer Error
ANSWER :
D. 3.9 × 10⁻¹⁰ m/s
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