The current gets back to the battery since the metallic body of the car acts as the other terminal through

Question

The diagram shows part of a car electrical system, which operates some of the lights.

(a) The diagram only shows one lead form the battery to each bulb, but a complete circuit must have two. How does the current get back to the battery?

(b) If a car owner adds extra lights to the car, why must the paint be removed from the body where the electrical con tact is made?

(c) (i) The two rear lights are wired up incorrectly, and only light faintly. Why do they light faintly?

(ii) Draw a diagram to show how the wires should be connected to make the lights shine normally?

(d) There are four side lights, and a number plate light. Each bulb is labeled 12 V, 4 W.

(i) What does the label mean?

(ii) How much current flows through each bulb assuming that it is connected properly?

(iii) How much current does the battery supply to these bulbs altogether?

(e) If the lights are on, they go dim when the car is started. Why?

Answer 1

(a) The current gets back to the battery since the metallic body of the car acts as the other terminal through which the current comes back to the battery after completing the circuit.

(b) In order to make an electric contact, the paint which acts as an insulator, must be removed from the body where the electric contact is made.

(c) (i) The two rear lights shine dimly. It may be due to the fact that the two rear light are connected in series.

(ii) See the circuit diagram below:

(d) Each bulb is labelled 12 V, 4 W, this means that when :

(i) Each of the bulb is connected to a supply of 12 W, the power consumed by each bulb is 4 W.

(ii) Since the lights are supposed to be connected in parallel p.d. across each is 12 V. Since P = Vt

i = P/V = 4/12 = 0.33 Amperes.

Total current supplied by the battery is (0.33 + 0.33 + 0.33 + 0.33 + 0.33) Amp.

= 0.33 x 5 = 1.65 Amp.

(e) If the car starts, when the lights are on, the light go dim because a part of the e.m.f. is used in operating the self starter.