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NEET2026PhysicsChapterActual

A galvanometer is connected in series with a 280 resistance and a battery of negligible internal resistance. The galvanometer shows a deflection of 60 divisions. When a shunt of 28 is connected across the galvanometer, its deflection reduces to 20 divisions. The resistance of the galvanometer is

Options

  1. A56
  2. B70
  3. C84
  4. D140

Correct answer

B. 70

Step-by-step solution

Let G be the resistance of the galvanometer and E be the EMF of the battery. Initial current through the galvanometer is I₁ = E 280 + G . Since deflection is proportional to current, I₁ = 60k , where k is a constant of proportionality. When a shunt of 28 is connected, the equivalent resistance of the galvanometer and shunt is R_ eq = 28G 28 + G . Total resistance of the circuit becomes R_ total = 280 + 28G 28 + G . The new main current is I₂ = E 280 + 28G 28 + G . Current through the galvanometer is I_g = I₂ 28 28

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