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Physics

Observe the electric circuit below and answer the questions that follow.

Observe the electric circuit below and answer the questions that follow. Physics Competency Focused Practice Questions Class 10 Solutions.

(a) If we increase the current in the above circuit using a rheostat, will the reading of the voltmeter decrease or increase?

(b) Give a reason for your answer in ‘a’.

(c) The present reading of the voltmeter is 2 V, and the current in the circuit is 0.8 A. Calculate the potential drop when the current in the circuit becomes 1 A. Given E = 3 V.

Current Electricity

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Answer

(a) Decrease.

(b) This is because the voltmeter shows terminal voltage. Increase in current increases potential drop which decreases terminal voltage.

(c) Potential drop = EMF - Terminal voltage

Potential drop = 3 - 2 = 1 V

Let internal resistance = r

Potential drop=I×r⇒r=Potential dropI⇒r=10.8=1.25 Ω\text {Potential drop} = \text{I} \times \text {r} \\[1em] \Rightarrow \text {r} = \dfrac{\text {Potential drop}}{\text{I}} \\[1em] \Rightarrow \text r = \dfrac {1}{0.8}=1.25\ Ω

New current = 1 A

New potential drop = 1 × 1.25 = 1.25 V

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