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NEET2026PhysicsChapterActual

In the given circuit, the galvanometer G shows zero deflection. Assuming the batteries are ideal, what is the value of the unknown resistance R ?

Options

  1. A15
  2. B20
  3. C30
  4. D60

Correct answer

A. 15

Step-by-step solution

Since the galvanometer shows zero deflection, no current flows through the middle branch. This means the same current I flows through the 10 , 20 , and R resistors in the right branch. Let the potential of the bottom wire be 0 V . The potential of the top wire is 30 V due to the battery on the left. The middle branch connects the 0 V line to the node between the 20 resistor and R . For zero current in the galvanometer, the potential at this node must be equal to the EMF of the 10 V battery. Thus, the potential diff

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