When a battery sends current through the resistances $R_1$ and $R_2R$, the internal resistance of battery is :
A
√R1R22
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B
√R1R2
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C
R1−R22
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D
R1+R22
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Solution
The correct option is D√R1R2 Here current through the resistance R1 is I1=εr+R1 and current through the resistance R2 is I2=εr+R2. Also the heat produced due to passage of current through both the resistances is same. Hence, Q=I21R1=I22R2 Using the values of I1 and I2 in above equation we get (εr+R1)2R1=(εr+R2)2R2 where, ε is the emf and r is the internal resistance of battery. ε2R1(r+R1)2=ε2R2(r+R2)2 r2(R1−R2)=R1R2(R1−R2) r2=R1R2 ∴r=√R1R2