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Chapter 19: Q28Q (page 796)

You are marooned on a desert island full of all kinds of standard electrical apparatus including a sensitive voltmeter, but you don’t have an ammeter. Explain how you could use the voltmeter to measure currents.

Short Answer

Expert verified

To convert a voltmeter to an ammeter, a small resistance is connected in parallel to it. The voltage reading of the voltmeter divided by the small resistance gives the current reading.

Step by step solution

01

Given data

A voltmeter is provided.

02

Parallel resistances

The equivalent resistance of multiple resistances connected in parallel is smaller than the smallest resistance connected.

03

Determination of the procedure to convert a voltmeter to an ammeter

A voltmeter has very high resistance and an ammeter has very low resistance. To negate the high resistance of the voltmeter, a small resistance is connected in parallel to it. The equivalent resistance is then very small. The voltage reading of the voltmeter divided by the small resistance connected in parallel gives the current reading because most of the current passes through the small resistance. Hence it can be used as an ammeter.

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