Chapter 14 Electric Current

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

• Electrons only

• Negative ions only

• Holes and electrons

• Lattice atoms and fee electrons

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?

• 3.8 A

• 4.2 A

• 6.0 A

• 10 A

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?

• 8.3 s

• 12 s

• 16 s

• 19 s

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?

• 1.6 $\times10^{-2}\ m\ s^{-1}$  

• 3.9 $\times10^{-2}\ m\ s^{-1}$  

• 3.0 $\times10^{-3\ }m\ s^{-1}$  

• 6.2 $\times10^{-3\ }m\ s^{-1}$  

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

• It is directly proportional to the diameter of the conductor.

• It is inversely proportional to the current.

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

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

 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?

• 2.5 $\times10^{23}$  

• 2.9 $\times10^{23}$  

• 4.2 $\times10^{23}$  

• 5.0 $\times10^{23}$  

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?

• 1.81 $\times10^3$  s

• 2.77 $\times10^3$  s

• 4.51 $\times10^3$  s

• 7.25 $\times10^3$  s

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.

• 1.0 $\times10^3A\ m^{-2}$  

• 6.9 $\times10^6A\ m^{-2}$  

• 2.1 $\times10^9A\ m^{-2}$  

• 1.1 $\times10^9A\ m^{-2}$  

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?

• 2.2 $\times10^4A\ m^{-2}$

• 2.8 $\times10^4A\ m^{-2}$

• 7.6 $\times10^7A\ m^{-2}$

• 5.6 $\times10^8A\ m^{-2}$

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? 

• 1.04 $\times10^{-4}m\ s^{-1}$  

• 3.10 $\times10^{-4}m\ s^{-1}$  

• 1.67 $\times10^{-3}m\ s^{-1}$  

• 1.90 $\times10^{-3}m\ s^{-1}$