Current Electricity and Electrical InstrumentHard

Question

In the adjacent circuit, AB is a potentiometer wire of length 40 cm and resistance per unit length 50Ω/m. As shown in the figure, the free end of an ideal voltmeter is touching the potentiometer wire. What should be the velocity of the jockey as a function of time so that reading in the voltmeter varies with time as (2 sin πt) ?
           

Options

A.(10 π sin πt) cm/s
B.(10 π cot πt) cm/s
C.(20 π sin πt) cm/s
D.(20 π cot πt) cm/s

Solution

           
Iwire = = 0.2 A
Potential difference across voltmeter, V = Ir - 2
⇒ 2 sin πt = 0.2 × 50 x - 2
⇒ 2 πcos πt = 10 V
⇒ V = 20 π (cos πt) cm/s

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