Question

A galvanometer of resistance 100 omega gives full scale deflection for 20mV. Find the resistance to be attached so that it gives full scale deflection of 5V

Answer 1

Answer:to act as a voltmeter 24.9 kilo ohms should be connected in series

Explanation:I have attached a solution

Sorry for the bad handwriting

Answer 2

Concept:

• Galvanometer
• Internal resistances
• Attaching a resistor in series to increase the voltage range

Given:

• Resistance of the galvanometer G = 100 ohm
• Original voltage = 20 mV = 0.02 V
• Final voltage = 5 V

Find:

• The resistance to be attached to increase the voltage range of the galvanometer

Solution:

The maximum current that can be carried by the galvanometer

I = Original voltage/ Galvanometer Resistance

I = 0.02/100 = 0.0002 A

The resistance has to be connected in series to increase the potential drop.

Let the resistance to be connected in series be r.

Final voltage = I (G+r)

5 = 0.0002 (100+r)

25000 = 100 + r

r = 24900 ohm

The resistance to be attached in series is 24900 ohms.

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