JEE PYQ: Current Electricity Question 76
Question 76 - 2019 (12 Jan 2019 Shift 2)
An ideal battery of 4 V and resistance R are connected in series in the primary circuit of a potentiometer of length 1 m and resistance $5,\Omega$. The value of R, to give a potential difference of 5 mV across 10 cm of potentiometer wire is:
(1) $490,\Omega$
(2) $480,\Omega$
(3) $395,\Omega$
(4) $495,\Omega$
Show Answer
Answer: (3)
Solution
Resistance of 10 cm wire $= 5 \times 0.1 = 0.5,\Omega$. $I = \frac{4}{R + 5}$. $V = I \times 0.5 = \frac{4 \times 0.5}{R + 5} = 5 \times 10^{-3}$. $\frac{2}{R+5} = 5 \times 10^{-3}$. $R + 5 = 400$. $R = 395,\Omega$.
BETA
