Chapter 22, Problem 46A

a.

To determine

The device which transforms electrical energy to mechanical energy.

Explanation of Solution

Introduction:

A motor converts electrical energy into mechanical energy.

  

Device number 4 in the figure is the motor which converts electrical energy into mechanical energy.

b.

To determine

The device which transforms chemical energy to electrical energy.

Explanation of Solution

Introduction:

A battery converts chemical energy to electrical energy.

  

Device number 1 in the figure is the battery which converts chemical energy to electrical energy.

c.

To determine

The device which turns the circuit on and off.

Explanation of Solution

Introduction:

A key is used in a circuit to turn it on and off.

  

Device number 2 in the fig is the key which turns the circuit on and off.

d.

To determine

The device whichprovides a way to adjust the speed.

Explanation of Solution

Introduction:

A rheostat is a device used to control current by varying the resistance.

  

Device number 3 in the figure is the rheostat which is used to control current by varying the resistance. For more speed more current is required. From Ohm’s law, $I=\frac{\text{V}}{R}$ , one can deduce that less resistance means more current and hence more speed in the motor and vice versa.

Conclusion:

Device number 3 in the figure is the rheostat which is used to control current by varying the resistance.