Question

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

Answer 1

a. `6 V`

b. `4V`

Explanation:

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

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`

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`