When a high resistance voltmeter is connected directly across a resister its reading is 2 V. An electric cell is sending the current of 0.4A, (measured by an ammeter) in the electric circuit in which a rheostat is also connected to vary the current.
Find the resistance of the resister.
Since the voltmeter reading shows 2V. Thus V = 2.
Also, Current send by electric cell = 0.4A
Thus I = 0.4A
By Ohm’s law V = IR
⇒ 2 = 0.4 × R
⇒ 
The resistance of the resistor is 5Ω.
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