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Why can't voltage be measured by an ammeter?

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zaraqkhan141 | Student | eNoter

Posted March 22, 2012 at 4:00 AM via web

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Why can't voltage be measured by an ammeter?

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enotechris | College Teacher | (Level 2) Senior Educator

Posted March 22, 2012 at 5:39 AM (Answer #1)

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Both voltmeters and ammeters are descended from the galvanometer, which can be modified and transformed into either a voltmeter or ammeter.  

An ammeter measures the amount of current flowing in a circuit, and is composed of a galvanometer placed in parallel with a resistor.

A voltmeter measures the amount of potential current that can flow in a circuit, and is composed of a galvanometer placed in series with a resistor. 

Although one measures the flow of current and the other the potential current, and because they are constructed of the same components, an ammeter can be used to measure the voltage if it is wired in parallel with the circuit, and the resistor changed from high resistance to low resistance.

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