Question

Vinita and Ahmed demonstrated a circuit that operates the two headlights and the two sidelights of a car, in their school exhibition. Based on their demonstrated circuit, answer the following questions.

1. State what happens when switch A is connected to:
   a) Position 2
   b) Position 3
2. Find the potential difference across each lamp when lit.
3. Calculate the current.
   a) in each 12 Ω lamp when lit.
   b) In each 4 Ω lamp when lit.
   OR
4. Show, with calculations, which type of lamp, 4.0 Ω or 12 Ω, has the higher power.

Answer 1

1. (a) 12 Ω lamps (only) on.
   (b) 4 Ω lamps (only) on.
2. 12 V for both sets of lamps and all of them are in parallel.
3. a) 12 Ω lamps are on when the wire is connected to position 2.
   The voltage across both 12 Ω lamps = 12 V.
   V = IR (Ohm’s law)
   `"I" = "V"/"R" = 12/12 = 1 "A"`
   b) 4 Ω lamps are on when the wire is connected to position 3.
   The voltage across both 4 Ω lamps = 12 V.
   V = IR (Ohm’s law)
   `"I" = "V"/"R" = 12/4 = 3 "A"`
   OR
4. `"P" = "V"^2/"R"`
   All lamps are in parallel and hence the same V for all lamps.
   For 4 Ω lamps → P = `(12 xx 12)/4` = 36 W
   For 12 Ω lamps → P = `(12 xx 12)/12` = 12 W
   Hence 4 Ω lamps will have higher power.