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What is the full-scale voltage of a meter movement that has a full-scale current of...

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hardworking-h... | (Level 2) eNoter

Posted September 11, 2013 at 2:59 PM via web

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What is the full-scale voltage of a meter movement that has a full-scale current of 500-uA and an internal resistance of 400 ohms?

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valentin68 | College Teacher | (Level 3) Associate Educator

Posted September 11, 2013 at 3:42 PM (Answer #1)

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An ammeter measures currents by passing this the current to be measured through a mobile coil, and thus creating a proportional magnetic field. This field, in turn interacts with a second magnetic field created by a permanent magnet leading to a deflection of the indicator (mobile coil) proportional to the current passing through it. Because aways a coil has a resistance, there will be a voltage drop U onto this. The Ohm law states the relation between the current passing through the mobile coil  I and its internal resistance R.

`I = U/R`

Therefore the full scale voltage using the problem data is

`U = I*R =500*10^-6 *400 = 0.2 "Volt"`

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