First slide

Power in a.c. circuit

Question

What is the r.m.s. value of an alternating current which when passed through a resistor produces heat which is thrice of that produced by a direct current of 2 amperes in the same resistor?

Easy

A

6 A
B

2 A
C

3.46 A
D

0.66 A

Solution

Heat produced by AC = 3 $\times$ Heat produced by DC
$∴ i_{rm}^{2} Rt = 3 \times i^{2} Rt \Rightarrow i_{rms}^{2} = 3 \times 2^{2}$
$\Rightarrow i_{rms} = 2 \sqrt{3} = 3 .46 A$

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