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Current Electricity question

2017 · Shift 0 · Q48
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Current Electricity question

2017 · Shift 0 · Q48

JEE MainPhysicsCurrent ElectricityMCQ+4 / −1
When a current of 5 mA is passed through a galvanometer having a coil of resistance 15 Ω\OmegaΩ, it shows full scale deflection. The value of the resistance to be put in series with the galvanometer to convert it into a voltmeter of range 0 – 10V is:
  1. A
    4.005 × 103 Ω\OmegaΩ
  2. B
    1.985 × 103 Ω\OmegaΩ
  3. C
    2.535 × 103 Ω\OmegaΩ
  4. D
    2.045 × 103 Ω\OmegaΩ
View written solutionFree

Correct answer: B

  1. Given data
  • Full scale deflection current of galvanometer: Ig=5 mA=5×10−3 AI_g = 5\text{ mA} = 5 \times 10^{-3}\text{ A}Ig​=5 mA=5×10−3 A
  • Resistance of galvanometer coil: G=15 ΩG = 15\,\OmegaG=15Ω
  • Desired voltmeter range: V=10 VV = 10\text{ V}V=10 V
  1. Condition for converting galvanometer into voltmeter

To convert a galvanometer into a voltmeter of range 000 to 10 10\,10V, a high resistance RRR is connected in series with the galvanometer.

At full scale deflection, the galvanometer current is IgI_gIg​, so: V=Ig(G+R)V = I_g(G + R)V=Ig​(G+R)

  1. Substitute the values

10=5×10−3(15+R)10 = 5 \times 10^{-3}(15 + R)10=5×10−3(15+R)

  1. Solve for RRR

15+R=105×10−3=200015 + R = \frac{10}{5 \times 10^{-3}} = 200015+R=5×10−310​=2000

So, R=2000−15=1985 ΩR = 2000 - 15 = 1985\,\OmegaR=2000−15=1985Ω

  1. Write in scientific notation

R=1.985×103 ΩR = 1.985 \times 10^3\,\OmegaR=1.985×103Ω

  1. Match with the options

This corresponds to:

Option B: 1.985×103 Ω1.985 \times 10^3\,\Omega1.985×103Ω

  1. Comparison with stored correct answer

Stored correct answer is B, which matches our derived answer.

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