Question

A galvanometer has a resistance of 40 ohms and a current of 4mA is needed for a full scale deflection. What is the resistance and how is it to be connected to convert the galvanometer​

Answer 1

Answer:

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Explanation:

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Answer 2

Given info : A galvanometer has a resistance of 40 ohms and a current of 4mA is needed for a full scale deflection.

To find : what is the resistance and how is it to be connected to convert the galvanometer

1. into an ammeter with a range of 0.3 A
2. into a voltmeter with a range of 0.2 volts.

solution : 1. to convert the galvanometer into an ammeter, we should connect a resistance (shunt) in parallel with it.

here resistance of Galvanometer, G = 40 ohm

resistance of shunt = S

current through the galvanometer, Ig = 4mA

I = 0.3 A

using formula, S = Ig × G/(I - Ig)

= 4 × 10¯³ × 40/(0.3 - 4 × 10¯³)

= 0.16/(0.3 - 0.004)

= 0.16/0.296

= 0.54 ohm

2. To convert the galvanometer into a voltmeter, we should connect a resistance in series combination with it.

here resistance is R

from Ohm's law, V = Ig(R + G)

here Ig = 4mA , G = 40 ohm, V = 0.2 volts

so, 0.2 = 4 × 10¯³(R + 40 )

⇒50 = R + 40

⇒R = 10 ohm

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