Free Printable Chapter 14 Electric Current

1.

An electrical fan rotates when the equipment is switched on . What are the charge carries that convey the current in the fan?

a)

Electrons only

b)

Negative ions only

c)

Holes and electrons

d)

Lattice atoms and fee electrons

2.

When a conductor carries a current, the number of conduction electrons that flow in the conductor for 10 s is 3.75 $\times10^{20}$ . What is the current that flows in the conductor?

a)

3.8 A

b)

4.2 A

c)

6.0 A

d)

10 A

3.

A neon lamp is connected to a battery. If a constant current of 1.25 A flows to the lamp, how long will it take for a charge of 15 C to flow through the lamp?

a)

8.3 s

b)

12 s

c)

16 s

d)

19 s

4.

A conductor of cross-sectional area 0.10 $mm^2$ carries a current of 2.5 A. If the number of conduction electrons per cubic metre is $1.0\times10^{28\ }$ $m^{-3}$ . What is the value of drift velocity of the free electrons in the conductor?

a)

1.6 $\times10^{-2}\ m\ s^{-1}$

b)

3.9 $\times10^{-2}\ m\ s^{-1}$

c)

3.0 $\times10^{-3\ }m\ s^{-1}$

d)

6.2 $\times10^{-3\ }m\ s^{-1}$

5.

Which statement is true about the drift velocity of the electrons in a current-carrying metallic conductor?

a)

It is directly proportional to the diameter of the conductor.

b)

It is inversely proportional to the current.

c)

It is inversely proportional to the number of conduction electrons per unit volume.

d)

It is directly proportional to the resistance of the conductor if the potential difference across the conductor is kept constant.

6.

A conductor of length 2.0 m and cross-sectional area 5.0 $\times10^{-6}\ m^2$ carries a current of 6.0 A. If the drift velocity of the conduction electrons is 1.5 $\times10^{-4}\ m\ s^{-1}$ , what is the number of electrons in the conductor?

a)

2.5 $\times10^{23}$

b)

2.9 $\times10^{23}$

c)

4.2 $\times10^{23}$

d)

5.0 $\times10^{23}$

7.

A tungsten wire of length 1.00 m and cross-sectional area 2.01 $\times10^{-6}\ m^2$ carries a current of 5.00 A. If the number of free electrons per unit volume is 4.3 $\times10^{28}$ , what is the time taken by an electron to travel from one end of the wire to the other end?

a)

1.81 $\times10^3$ s

b)

2.77 $\times10^3$ s

c)

4.51 $\times10^3$ s

d)

7.25 $\times10^3$ s

8.

There are 6.23 $\times10^{24}$ free electrons per $cm^3$ in a wire. The average drift velocity of the electrons is 1.1 $\times10^{-3}m\ s^{-1}$ . Calculate the current density in the wire.

a)

1.0 $\times10^3A\ m^{-2}$

b)

6.9 $\times10^6A\ m^{-2}$

c)

2.1 $\times10^9A\ m^{-2}$

d)

1.1 $\times10^9A\ m^{-2}$

9.

A charge of 60 Coulomb flows in a wire for 45 minutes. If the diameter of the wire is 1.0 mm, what is the current density in the wire?

a)

2.2 $\times10^4A\ m^{-2}$

b)

2.8 $\times10^4A\ m^{-2}$

c)

7.6 $\times10^7A\ m^{-2}$

d)

5.6 $\times10^8A\ m^{-2}$

10.

A current flows in a copper wire. The current density in the wire is 1.4 $\times10^6A\ m^{-2}$ . If the number of free electrons in 1 $m^3$ of wire is 8.4 $\times10^{28}$ , what is the drift velocity of the electrons?

a)

1.04 $\times10^{-4}m\ s^{-1}$

b)

3.10 $\times10^{-4}m\ s^{-1}$

c)

1.67 $\times10^{-3}m\ s^{-1}$

d)

1.90 $\times10^{-3}m\ s^{-1}$

11.

A copper wire of length 2.0 m has resistance 20 $\Omega$ . The wire is stretched to an extension of 0.001m. If the volume of the wire remains unchanged, what is the new resistance of the wire?

a)

20.01 $\Omega$

b)

20.02 $\Omega$

c)

20.03 $\Omega$

d)

20.04 $\Omega$

12.

A hollow copper rod has an inner radius of 0.65 cm and an outer radius of 1.0 cm as shown in the diagram. A current flows from P to Q. If the length of the rod is 20 cm and its resistivity is 1.7 $\times10^{-8}\Omega\ m$ , what is the resistance of the copper rod?

a)

3.4 $\times10^{-9}\Omega$

b)

1.9 $\times10^{-5}\Omega$

c)

1.8 $\times10^{-4}\Omega$

d)

2.9 $\times10^{-3}\Omega$

13.

The conductivity of a copper wire decrease as the temperature increases because

a)

the number of free electrons decreases.

b)

the lattice atoms vibrate with smaller amplitude.

c)

the drift velocity of the electrons decreases.

d)

the mean time between collision decreases.

14.

The figure shows a cable which consists of a wire X of resistivity $\rho$ , cross-sectional area A and length $l$ , and four wires of metal Y of resistivity 3 $\rho$ , each with cross-sectional area 2A and of the same length. Find the resistance of this cable in terms of $\rho$ ,A and $l$ .

a)

$\frac{3\rho l}{11A}$

b)

$\frac{7\rho l}{A}$

c)

$\frac{5\rho l}{2A}$

15.

The conductivity of copper is 6.0 $\times10^7\Omega^{-1}m^{-1}.$ The free electron density copper is 8.45 $\times10^{28}m^{-3}$ . Estimate the mean time between collisions of free electrons and positive ions in copper.

a)

2.52 $\times10^{-14}\ s$

b)

4.04 $\times10^{-33}\ s$

c)

4.04 $\times10^{-14}\ s$

d)

7.10 $\times10^{-22}\ s$

Chapter 14 Electric Current

Total questions: 15

Worksheet time: 26mins

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