JEE PYQ: Current Electricity Question 33
Question 33 - 2020 (08 Jan 2020 Shift 2)
The series combination of two batteries, both of the same emf 10 V, but different internal resistance of $20,\Omega$ and $5,\Omega$, is connected to the parallel combination of two resistors $30,\Omega$ and $R,\Omega$. The voltage difference across the battery of internal resistance $20,\Omega$ is zero, the value of $R$ (in $\Omega$) is ____.
Show Answer
Answer: 30
Solution
Total EMF = 20 V, total internal resistance = 25 $\Omega$. For voltage across 20 $\Omega$ battery to be zero: $10 = i \times 20$. $i = 0.5$ A. Also $i = \frac{20}{25 + R’}$ where $R’ = \frac{30R}{30+R}$. $0.5 = \frac{20}{25 + R’}$, $R’ = 15$. $\frac{30R}{30+R} = 15$. $30R = 450 + 15R$. $R = 30,\Omega$.
BETA
