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  • (a) Why do we use a shunt to convert a galvanometer into an ammeter? (b) A galvanometer of resistance 15 shows a full scale deflection on meter scale for a

(a) Why do we use a shunt to convert a galvanometer into an ammeter?

(b) A galvanometer of resistance 15\Omega shows a full scale deflection on meter scale for a current of 6mA. Calculate the value of the shunt resistance required to convert the galvanometer into an ammeter of range 0 - 6A.

 

 
 
 
 
 

Answers (1)

An ammeter is used to measure current in the circuit. So it is connected in series with the circuit. For getting proper measurement ammeter must offer low resistance. When galvanometer connect in series with circuit if offer a resistance 'R4' and it will change the current in the circuit. So to reduce the resistance connect a low resistance in parallel with the galvanometer. That low resistance is called Shunt resistance and resistance provided by it is 'r1'. It also helps to protect the galvanometer coil from excessive current flow.

The effective resistance = \frac{R_{G}r_{s}}{R_{G}+r_{s}}\cong r_{s} which is very small

(b) Given, 

Galvanometer resistance R_{G}= 15\Omega

Galvanometer current I_{g}= 6mA

Total current I= 6A

To convert a galvanometer into ammeter connect a shunt resistance in parallel with the galvanometer.

We know,

shunt resistance = \frac{I_{g}R_{G}}{I-I_{g}} 

                                           

 = \frac{0.006 \times 15}{6-0.006}= 0.01515\Omega= 15m\Omega

Connect 15m\Omega resistance parallel to galvanometer to make it an ammeter.

Posted by

Safeer PP

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