What is the reading of the voltmeter when switch is off and on?

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1 Answer
Feb 24, 2018

a. #6 V#

b. #4V#

Explanation:

When the switch is off,current will not be flowing through the distal #100 Omega# resistor,

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So,current flowing through the circuit is #12/(100+100) = 0.06 A#

So,reading of voltmeter will be equals to the potential drop across it, i.e #I*R=0.06*100=6 V#

When the switch is on,the distal #100 Omega# resistor is in parallel with with the resistance of the voltmeter,so their equivalent resistance is #(100*100)/(100+100)=50 Omega#enter image source here

Again,the other #100 Omega# resistor is in series with that,so,net resistance of the circuit is #100+50=150 Omega#

Now,current flowing through the circuit =# 12/150=0.08 A#

So,voltage drop across #100 Omega# is #100*0.08=8 V#

So,rest #(12-8)=4 V# will drop across the voltmeter and the distal #100 Omega# as they are in parallel combination.

So,now voltmeter reading will be #4 V#