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MHT CET · Physics · Current Electricity

When an additional resistance \(1980 \Omega\) is connected in series with a voltmeter, each scale division has 100 times larger value. The resistance of the voltmeter is

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

Answer & Solution

Correct Answer

(B) \(20 \Omega\)

Step-by-step Solution

Detailed explanation

Let \(R\) be the resistance of voltmeter. Let \(n\) be the number of divisions in the voltmeter. Then the voltage \(V\) recorded by each division of voltmeter when current \(i_g\) flow through it is
\(i_g \frac{R}{n}=V\qquad(1)\)
When resistance is connected in series with voltmeter, then
\(i_g \frac{(R+1980 \Omega)}{n}=100 V\qquad(2)\)
Dividing (2) by (1), we get
\(R+1980 \Omega=100 R\)
\(\Rightarrow R=\frac{1980}{99} \Omega=20 \Omega\)
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