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Question

A resistance of 20 ohms is connected to a source of an alternating potential V=220 sin(100 πt). The time taken by the current to change from its peak value to r.m.s value is

A
0.2 sec
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B
0.25 sec
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C
25×103sec
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D
2.5×103sec
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Solution

The correct option is D 2.5×103sec
Step 1, Given data

Resistance = 20 ohm

Voltage = V=220 sin(100 πt)

Step 2, Finding the time

Peak value to r.m.s. value means, current becomes 12 times.

From the question

V=220sin100πt

So, we can write

i=i0sin100πt

Now,

12×i0=i0sin100πt

Or, sinπ4=sin100πt

Or, t=1400 sec=2.5×103 sec

Hence, option (C) is correct


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