1Electrical Power. Joule’s law. Current supply efficiency

 (I) Individual End-up-Chapter questions

1    A car headlamp when connected to a 12 V battery converts energy at a rate of 50 W.
How much energy is converted when it is switched on for 5 minutes?                                       [1]

A   2 J

B   120 J

C   300 J

D   150 000 J

2    A current of 2.0 A passes through a component of resistance 24 W.
What is the rate of energy transfer?                                                                                         [1]

A   6 W

B   12 W

C   48 W

D   96 W

3    A 12 V, 36 W lamp is operated for 1 hour (3600 s). Calculate:

a    the energy dissipated by the lamp                                                                                      [2]

b    the current in the lamp.                                                                                                      [2]

4    A 100 W resistor can safely dissipate 0.25 W. Calculate the maximum current in the resistor.     [3]

5    A filament lamp in a small torch is labelled as ‘1.5 V, 400 mA’. The filament lamp transfers 5.0% of the electrical energy into light and the remainder is dissipated as heat. Calculate:

a    the power rating of the lamp                                                                                              [2]

b    the power radiated as light                                                                                                 [2]

c    the resistance of the filament lamp.                                                                                    [2]