(a) Why is a high resistance required to convert a galvanometer into a voltmeter?

(b) A galvanometer coil has a resistance of 12\; \Omega and the meter shows full scale deflection for a current of 3 mA. How will you convert it into a voltmeter of range 0 to 18 V?

 

 

 

 
 
 
 
 

Answers (1)
S safeer

(a) A galvanometer can convert into a voltmeter by connecting a high resistance series to the galvanometer.A voltmeter is used to measure potential difference between two points in a circuit . for this it should connect parallel with that point of circuit.

The reason for using high resistance is the measurement should become accurate, for thus, it must not draw current, so, high resistance is added series with galvanometer.

(b) Given, 

 Galvanometer Resistance =12\; \Omega 

Galvanometer full-scale deflection current =3\; mA

The required range of the voltmeter =0\; to\; 18 V

To convert Galvanometer into voltmeter connect a resistance series,

with the galvanometer,

By ohm's law, V=IR

                        R=\frac{V}{I}

Here,             R=R_{h}+R_{s}

                       \frac{V}{I}=R_{h}+R_{s}\; ;\; \; \; R_{s}=\frac{V}{I_{s}}-h

                        R_{s}=\frac{18}{0.03}-12\Rightarrow R_{s}=5988\; \Omega

 

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