A copper wire of cross-sectional area 1 mm² carries a current of 1.7 A. The number density of free electrons in copper is 8.5 × 10²⁸ m^-3. The drift speed of the electrons is (e = 1.6 × 10^-19 C):

A8 × 10³ m/s
B1.25 × 10^-2 m/s
C1.25 × 10^-4 m/s
D1.25 × 10² m/s

Q4. AI-generated practice Single-correct MCQ Medium

The same current flows through two wires of the same metal, the radius of the second being half that of the first. The drift speed in the second wire is:

A
one quarter of that in the first
B
4 times that in the first
C
2 times that in the first
D
the same as in the first

Q5. AI-generated practice Single-correct MCQ Medium

The potential difference across a metallic wire is doubled while its temperature is kept constant. The drift speed of the free electrons:

A
becomes four times
B
remains unchanged
C
is halved
D
doubles

Q6. AI-generated practice Single-correct MCQ Easy

Electrons in a conductor have a drift speed of 2 × 10^-4 m/s in an electric field of 0.5 V/m. Their mobility is:

A4 × 10^-2 m² V^-1 s^-1
B4 × 10^-4 m² V^-1 s^-1
C2.5 × 10³ m² V^-1 s^-1
D1 × 10^-4 m² V^-1 s^-1

Q7. AI-generated practice Single-correct MCQ Hard

A metal wire is stretched uniformly to twice its original length, and the same potential difference as before is applied across it. The drift speed of the electrons becomes:

A
one quarter of the original value
B
half of the original value
C
unchanged
D
twice the original value

Q8. AI-generated practice Single-correct MCQ Medium

A current of 5 A flows through a wire of cross-sectional area 2 mm². The current density is:

A2.5 × 10⁶ A/m²
B1 × 10^-5 A/m²
C2.5 × 10³ A/m²
D2.5 A/m²

Q9. AI-generated practice Single-correct MCQ Easy

The drift speed of electrons in a wire is only about 10^-4 m/s, yet a bulb lights up almost instantly when switched on. This is because:

A
the electric field is set up along the whole wire almost instantly, so electrons everywhere start drifting at once
B
the bulb has very low resistance
Cthe thermal speed of electrons is about 10⁵ m/s
D
electrons from the switch reach the bulb at nearly the speed of light

Q10. AI-generated practice Single-correct MCQ Medium

A steady current flows through a metal conductor whose cross-section narrows from one end to the other. Along the conductor:

A
the drift speed is the same everywhere
B
the current is larger where the cross-section is larger
C
the current is the same everywhere, but the drift speed is larger where the cross-section is smaller
D
both the current and the drift speed are larger where the cross-section is larger

Q11. AI-generated practice Single-correct MCQ Hard

The charge flowing through a cross-section of a conductor varies with time as q = (3t² + 2t) C, where t is in seconds. The current at t = 2 s is:

A
14 A
B
12 A
C
16 A
D
8 A

Q12. AI-generated practice Single-correct MCQ Medium

Two wires of the same metal, with diameters 1 mm and 2 mm, are connected in series and carry a current. The ratio of the drift speed in the thinner wire to that in the thicker wire is:

A
1 : 4
B
2 : 1
C
4 : 1
D
1 : 2

Q13. AI-generated practice Single-correct MCQ Hard

In the Bohr model of hydrogen, an electron moves in a circular orbit of radius 0.5 Å with a speed of 2.2 × 10⁶ m/s. The equivalent current due to its motion is about (e = 1.6 × 10^-19 C):

A
1.1 μA
B
0.56 mA
C
3.5 mA
D
1.1 mA

Q14. AI-generated practice Single-correct MCQ Medium

In a metallic conductor with no applied electric field, the average velocity of the free electrons is:

Aabout 10⁵ m/s
B
close to the speed of light
C
equal to the drift velocity
D
zero

Q15. AI-generated practice Numerical value Easy

A current of 2.5 A flows through a lamp for 4 s. Find the charge (in coulomb) that passes through the lamp.

Q16. AI-generated practice Numerical value Medium

A wire carries a current of 3.2 mA. If n × 10¹⁶ electrons pass a cross-section of the wire each second, find n. (e = 1.6 × 10^-19 C)

Q17. AI-generated practice Numerical value Medium

A wire of cross-sectional area 2 mm² contains 5 × 10²⁸ free electrons per m³ and carries a current of 3.2 A. If the drift speed is x × 10^-4 m/s, find x. (e = 1.6 × 10^-19 C)

Q18. AI-generated practice Numerical value Hard

A copper wire of cross-sectional area 1 mm² carries a steady current of 1.6 A. The free-electron density of copper is 8 × 10²⁸ m^-3. Find the time (in seconds) taken by an electron to drift through 0.5 m of the wire. (e = 1.6 × 10^-19 C)

Q19. AI-generated practice Assertion–Reason Medium

Assertion (A): The current in a conductor is the same at every cross-section, even where the area of cross-section changes.
Reason (R): In steady state, charge is conserved and does not accumulate anywhere in the conductor.

A
Both A and R are true and R is the correct explanation of A
B
Both A and R are true but R is not the correct explanation of A
C
A is true but R is false
D
A is false but R is true

Q20. AI-generated practice Assertion–Reason Hard

Assertion (A): In the absence of an electric field, the average velocity of the free electrons in a metal is zero.
Reason (R): In the absence of an electric field, the free electrons in a metal are at rest.

A
Both A and R are true and R is the correct explanation of A
B
Both A and R are true but R is not the correct explanation of A
C
A is true but R is false
D
A is false but R is true