Q. 485.0( 2 Votes )

# A voltmeter of re

Answer :

Concepts/Formula used:

Resistors in Series:

Resistors in parallel:

Ohm’s Law:

Potential Difference (V) across a resistor of resistance R when current I passes through it is given by Ohm’s law:

(a)

The given circuit is:

We can easily see that the voltmeter and R_{1} are in parallel. The equivalent resistance, r’ is given by:

We can redraw the circuit as follows:

Note that r’ and R_{2} are in series. The equivalent resistance is given by:

The current coming out of the battery also passes through r’. By Ohm’s law,

Now, the voltmeter reads the potential different across R_{1} .

Hence, the voltmeter reads 24V.

(b)

The given circuit is now:

The equivalent resistance is :

The current is the same throughout the circuit as all components are in series and is given by:

Now, the potential difference across R_{1} is given by:

Hence, the potential difference across the 100Ω resistor before connecting the voltmeter was 28V.

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