# Voltage-divider and d'Arsonval voltmeter problem

In summary: Ideal meters have infinite resistance.In summary, the voltage-divider circuit is designed to have a no-load output voltage of 8/10ths of the input voltage. A d'Arsonval voltmeter with a sensitivity of 200 ohms/V and a full-scale rating of 150 V is used to check the circuit. In part (a), when the voltmeter is placed across the 126 V source, it will read 126 V. For part (b), the equivalent circuit is drawn with an ideal meter and a resistor. Using the voltage divider equation, the voltage across the resistor is calculated to be 100.8 V. However, this is the voltage that an ideal meter would display, not the actual voltage
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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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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?

berkeman said:
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.

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

CWatters said:

Try drawing the equivalent circuit for the set up in b)
Here it is.

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• part b.PNG
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OK now replace the real world volt meter with an ideal meter and a resistor

CWatters said:
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?

Thats the voltage that an ideal meter would display not the voltage this meter would display. See my post #7.

## What is a voltage-divider?

A voltage-divider is a circuit that divides an input voltage into smaller output voltages. It is commonly used in electronic devices to regulate and control the voltage levels.

## What is a d'Arsonval voltmeter?

A d'Arsonval voltmeter is a type of analog voltmeter that uses the principle of electromagnetic induction to measure voltage. It consists of a coil suspended in a magnetic field, and the voltage to be measured is applied to the coil, causing it to deflect and indicate the voltage on a scale.

## What is the purpose of a voltage-divider in a d'Arsonval voltmeter?

The voltage-divider in a d'Arsonval voltmeter is used to reduce the input voltage to a level that is suitable for the voltmeter to measure. This is necessary because the voltmeter has a limited range and can only measure voltages within a certain range.

## What are some common problems with voltage-divider and d'Arsonval voltmeters?

One common problem with voltage-divider and d'Arsonval voltmeters is that they may experience errors due to external magnetic fields. Another problem is that the voltage-divider may introduce inaccuracies if it is not designed and calibrated correctly.

## How can these problems be addressed?

To address the issue of external magnetic fields, the voltmeter can be shielded or placed in a location with minimal magnetic interference. To avoid inaccuracies from the voltage-divider, proper design and calibration of the circuit are necessary. Additionally, using high-quality components and regularly checking and adjusting the voltmeter can also help improve accuracy.

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