Circuit with Ammeter and Voltmeter – Rankers Physics
Topic: Current Electricity
Subtopic: Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge )

Circuit with Ammeter and Voltmeter

Assertion (A): In the given circuit, when switch \(S\) is ON reading of ammeter and voltmeter will increase.
Reason (R): In parallel combination net resistance will reduce.
 
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Solution:

When switch \(S\) is ON, another resistor \(R\) is connected in parallel. The equivalent resistance of the parallel combination is \(R/2\), which is less than \(R\). Thus, the net resistance reduces (Reason R is true). The total current (ammeter reading) will increase. However, assuming an ideal voltage source, the voltage across the parallel combination (voltmeter reading) will remain constant (equal to the source EMF). Therefore, Assertion (A) is false as the voltmeter reading does not increase.

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