In which position could a switch be placed so that both lamps can be switched on or off at the same time?
Answer options:
A.
J
B.
K
C.
L
D.
M
How to approach this question
1. Analyze the circuit diagram. It shows a battery, an ammeter, and two lamps connected in parallel.
2. The current flows from the battery, through the ammeter, and then splits to go through the two lamps. After the lamps, the current rejoins and flows back to the battery.
3. To switch both lamps on or off together, the switch must be placed in a part of the circuit where the *total* current flows.
4. Consider each position:
- J and L are in the individual branches for each lamp. A switch here would only control one lamp.
- K is in the joining wire after the lamps.
- M is in the main circuit before the current splits.
5. Determine which position would interrupt the flow of current to the entire parallel section.
Full Answer
D.M✓ Correct
M
This circuit has two main parts: the series part and the parallel part.
- The **series part** contains the battery and the ammeter. The total current from the battery flows through this section. Position M is in this part.
- The **parallel part** contains the two lamps. The total current splits at the junction before the lamps, flows through each lamp, and then rejoins at the junction after the lamps. Positions J and L are in the individual parallel branches.
A switch acts as a break in the circuit.
- If a switch is placed at J or L, it will only break that specific branch, turning off only one lamp.
- If a switch is placed at M, it will break the main circuit before the current splits. This will stop the flow of current to the entire circuit, turning off both lamps simultaneously. This is the correct position for a master switch.
Common mistakes
✗ Choosing a position in one of the parallel branches (J or L).
✗ Not understanding that a switch must be in series with the components it is intended to control.
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