Objective 4-Be able to determine the reading of ammeters and voltmetersa) Find the voltage...

Objective 4-Be able to determine the reading of ammeters and voltmeters

a) Find the voltage v across the 75 kΩ resistor in the circuit shown.

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b) If the 150 V voltmeter of Example 1 is used to measure the voltage, what will be the reading?

Example 1

A 50 mV, 1 mA d’Arsonval movement is to be used in a voltmeter in which the full-scale reading is 150 V. Determine Rv.

Solution

Full-scale deflection requires 50 mV across the meter movement, and the movement has a resistance of 50 Ω. Therefore we apply Eq. 1 with R1 = Rv, R2 = 50, vs = 150, and v2 = 50 mV:

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Solving for Rv gives

Rv = 149,950 Ω.

Equation. 1

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