JEE Main 2016 · 9 Apr · Shift 1 · Physics Q14

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PhysicsSingle correct+4 / -1Question 14 of 90

In the circuit shown, the resistance r is a variable resistance. If for r = fR, the heat generation in r is maximum then the value of f is :

A cell in series with a resistor R and a parallel pair made of a second resistor R and a variable resistor r.

\dfrac14

\dfrac12

\dfrac34

Answer and worked solution

Official answer: B

The parallel pair $R\parallel r$ is in series with R. The voltage across r is $\dfrac{Er}{R+2r}$ , so $P_r=\dfrac{E^2r}{(R+2r)^2}$ , which is greatest at $r=\frac R2$ : $f=\frac12$ .

Topics:Electrical power and heating Series and parallel resistors

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JEE Main 2016 · 9 Apr · Shift 1, Physics question 14