# Voltage-divider and d'Arsonval voltmeter problem

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The voltage-divider circuit is designed so that the no-load output voltage is 8/10ths of the input voltage. A d'Arsonval voltmeter having a sensitivity of 200 ohms/V and a full-scale rating of 150 V is used to check the operation of the circuit.
a) What will the voltmeter read if it is placed across the 126 V source?
b) What will the voltmeter read if it is placed across the 60 kohms resistor?
c) What will the voltmeter read if it is placed across the 15 kohms resistor?
d) Will the voltmeter readings obtained in parts (b) and (c) add to the reading recorded in part (a)? Explain why or why not.

Output voltage is 100.8 V. About d'Arsonval voltmeter: using sensitivity and full-scale rating we can find resistance of the voltmeter? Than it is 30 kohms. I think in part (a) answer is 126 V, is it correct? Have some problems with parts (b)-(d). Thanks for sharing your thoughts!

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berkeman
Mentor
The voltage-divider circuit is designed so that the no-load output voltage is 8/10ths of the input voltage. A d'Arsonval voltmeter having a sensitivity of 200 ohms/V and a full-scale rating of 150 V is used to check the operation of the circuit.
a) What will the voltmeter read if it is placed across the 126 V source?
b) What will the voltmeter read if it is placed across the 60 kohms resistor?
c) What will the voltmeter read if it is placed across the 15 kohms resistor?
d) Will the voltmeter readings obtained in parts (b) and (c) add to the reading recorded in part (a)? Explain why or why not.

Output voltage is 100.8 V. About d'Arsonval voltmeter: using sensitivity and full-scale rating we can find resistance of the voltmeter? Than it is 30 kohms. I think in part (a) answer is 126 V, is it correct? Have some problems with parts (b)-(d). Thanks for sharing your thoughts!
Your answer for (a) is correct. Please show us your work on the rest of the parts of the problem. What is the equation for a Voltage Divider?

• Your answer for (a) is correct. Please show us your work on the rest of the parts of the problem. What is the equation for a Voltage Divider?
Voltage divider equation: Uout = Uin * R2 / (R1 + R2). And for my problem Uout = 126 V * 60 kohms / (60 kohms + 15 kohms) = 100.8 V.

CWatters
Homework Helper
Gold Member

Try drawing the equivalent circuit for the set up in b)

• CWatters
Homework Helper
Gold Member
OK now replace the real world volt meter with an ideal meter and a resistor

OK now replace the real world volt meter with an ideal meter and a resistor
Can I use this equations: U2 = I * R;
I = Uin/(R1 + R2)?
I = 126 V / (15 kohms + 60 kohms) = 1.68 mA; U2 = 1.68 mA * 60 kohms = 100.8 V. Is that correct?

CWatters