In the circuit, a voltmeter reads `30 V` when it is connected across 400 `Omega` resistance. Calculate what the same voltmeter will read when it is connected across the `300Omega` resistance?

Explanation

Ohm’s Law state that “the current through a conductor between two points is directly proportional to the voltage across the two points”.
Given that voltage across`400 Omega` after connecting voltmeter is 30 V that is half of applied emf 60 V. It shows that voltage is divided into two equal rests and thus `R_(AB)` will be equal to . `300 Omega, R=300 Omega`
`(400R)/(400+R)=300 implies R=1200`
Now if voltmeter is connected across `300 Omega` resistance
`R_(AC)=(300r)/(300+R)=(300 times 1200)/(300+1200)=240 Omega`, Now `V_(AC)=60/((240+400)) times 240=22.5` volts