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Question

Two identical heater wires are first connected in series and then in parallel with a source of electricity. The ratio of heat produced in the two cases ?

A
2:1
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B
1:2
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C
4:1
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D
1:4
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Solution

The correct option is D 1:4
Answer is D.

The heat energy E = Pt = (VI)t = I2Rt(V=IR).
Since the wires are identical, their resistances are equal. Let their individual resistance be R.
In series, the equivalent resistance is R+R = 2R.
Therefore, E1 = I2(2R)t=2(I2Rt).
In parallel, the equivalent resistance = R22R.
Therefore, E2 = I2(R22R)t=I2Rt2.
E1/E2 = 1/4.
Hence, the ratio is 1:4.

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