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4. Moving charges and magnetism — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics4. Moving charges and magnetism1 Mark
MCQ
The current sensitivity of a moving coil galvanometer increases by $20 \%$ when its resistance is doubled. Calculate, by what factor does the voltage sensitivity change?
  • ✓
    Becomes $\frac{3}{5}$ times
  • B
    Becomes $\frac{2}{5}$ times
  • C
    No change
  • D
    Decreases by a factor of $\frac{7}{5}$
✓

Answer

Correct option: A.
Becomes $\frac{3}{5}$ times
a
(a)

$S_{i_1}=\frac{N i A B}{k i}=\frac{N A B}{k}$

$S_{i_2}=\frac{1.2 N A B}{k}$

$S_{v_1}=\frac{N A B}{k R}=\frac{S_{i_1}}{R}$

$S_{v_2}=\frac{S_{i_2}}{2 R}=\frac{1.2(N A B)}{k(2 R)}$

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