Question

In the following circuit the resistance of the ammeter is 2 ohm and the resistance of the voltmeter is 30000 ohm what is the value of the resistance R when the ammeter reads 0.1A and the voltmeter reads 10 v​

Answer 1

Answer: The value of resistance R is 98 ohm.

Explanation: The ammeter is a device that measures current and is usually connected in series. While the voltmeter measures the potential difference between two points in a circuit and is usually connected in parallel.

Both the resistance and ammeter resistance are in series and the current in the ammeter is 0.1 Ampere, Then the voltage drop measured across R and ammeter together is 10 V which is measured by the voltmeter.

$R_{ammeter}=2\Omega \\R_{voltmeter}=30000\Omega \\Voltage\ drop\ across\ R\ and\ Ammeter=0.1\times (R+2)=10V\\R+2=100\\R=98\Omega$

Answer 2

Concept:

• Electric circuits
• Ammeters and voltmeters
• Ammeters usually have low internal resistance
• Voltmeters usually have high internal resistance
• Voltages
• Potential difference
• Resistance
• Internal resistances

Given:

• Resistance of the ammeter = 2 ohm
• Resistance of the voltmeter = 30,000 ohm
• Current = 0.1 A
• Potential difference = 10 V

Find:

• The resistance R when the ammeter reads 0.1 A and the voltmeter has a value of 10 V

Solution:

The current going through the voltmeter is negligible as the resistance of the voltmeter is too high.

So we assume that all the current moves through the ammeter loop.

V = IR

V = 0.1 (R +2)

V = 10V

10 =  0.1 (R +2)

100 = R +2

R = 98 ohm

The value of the resistance R is 98 ohms.

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