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CUET · PHYSICS · PYQ PAPER 2023

A resistance of \( 15\Omega \) is connected in series with an unknown resistance \( R_1 \). This combination is connected to one gap of a meter bridge, while a resistance \( R_2 \) is connected in the other gap. The balance point is at 50 cm. When \( 15\Omega \) is removed, the balance point shifts by 10 cm. The value of \( R_1 \) is

  1. A \( 20 \Omega \)
  2. B \( 30 \Omega \)
  3. C \( 40 \Omega \)
  4. D \( 60 \Omega \)
Verified Solution

Answer & Solution

Correct Answer

(B) \( 30 \Omega \)

Step-by-step Solution

Detailed explanation

\( \frac{15 + R_1}{R_2} = \frac{50}{100-50} = 1 \) \( 15 + R_1 = R_2 \) \( \frac{R_1}{R_2} = \frac{50-10}{100-(50-10)} = \frac{40}{60} = \frac{2}{3} \) \( \frac{R_1}{15 + R_1} = \frac{2}{3} \) \( 3R_1 = 2(15 + R_1) \) \( 3R_1 = 30 + 2R_1 \) \( R_1 = 30 \, \Omega \)