In the given circuit the internal resistance of the 18 V cell is negligible. If R1 = 400 Ω, R3 = 100 Ω and R4 = 500 Ω and the reading of an ideal voltmeter across R4 is 5V, then the value of R2 will be: (a) 300 Ω (b) 450 Ω (c) 550 Ω (d) 230 Ω

Answer: (a). Current in R₃, R₄ branch: 5/500 = 0.01 A; branch p.d. = 0.01 × 600 = 6 V (this is also across R₂). P.d. across R₁ = 18 - 6 = 12 V, so total current = 12/400 = 0.03 A. Current in R₂ = 0.03 - 0.01 = 0.02 A R₂ = 6/0.02 = 300 Ω. So the answer is (a).

In the given circuit the internal resistance of the 18 V cell is… | JEE Main 2019 (9 Jan, Shift 2)

Q165JEE Main 2019 · 9 JAN · SHIFT 2Medium

Kirchhoff's Laws & Measuring Instruments

In the given circuit the internal resistance of the 18 V cell is negligible. If R1 = 400 $\Omega$ , R3 = 100 $\Omega$ and R4 = 500 $\Omega$ and the reading of an ideal voltmeter across R4 is 5V, then the value of R2 will be:

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Answer: (a)

Current in $R_3, R_4$ branch: $\dfrac{5}{500} = 0.01\text{ A}$ ; branch p.d. $= 0.01 \times 600 = 6\text{ V}$ (this is also across $R_2$ ).
P.d. across $R_1 = 18 - 6 = 12\text{ V}$ , so total current $= \dfrac{12}{400} = 0.03\text{ A}$ .
Current in $R_2 = 0.03 - 0.01 = 0.02\text{ A}$
$R_2 = \dfrac{6}{0.02} = 300\ \Omega$ . So the answer is (a).

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