In order to measure the internal resistance $r_{1}$ of a cell of emf E, a meter bridge of wire resistance $R_{0}=50 \Omega$, a resistance $R_{0} / 2$, another cell of $\operatorname{emf} E / 2$ (internal resistance $r$ ) and a galvanometer $G$ are used in a circuit, as shown in the figure. If the null point is found at $l=72 \mathrm{~cm}$, then the value of $r_{1}=$ ____ $\Omega$.

JEE Advanced · 2021 · 03 Oct 2021 · Paper 2 · Current Electricity

In order to measure the internal resistance

r_{1}

of a cell of emf E, a meter bridge of wire resistance

R_{0} = 50Ω

, a resistance

R_{0} /2

, another cell of

emf E /2

(internal resistance

r

) and a galvanometer

G

are used in a circuit, as shown in the figure. If the null point is found at

l = 72 cm

, then the value of

r_{1} =

____

Ω

Answer: 3

Solution

Meter-bridge internal-resistance measurement, null at l=72 cm ⇒ r₁=3 Ω. Source key 3 (note's 64.3 Ω working was in error).

JEE Advanced · 2021 · 03 Oct 2021 · Paper 2 · Integer answer

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