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A voltmeter reads the potential differen...

A voltmeter reads the potential difference across the terminals of an old battery as `1.40 V`, while a potentiometer reads its voltage to be `1.55 V`. The voltmeter resistance is `280 Omega`.

A

The emf of the battery is `1.4 V`.

B

The emf of the battery is `1.55 V`.

C

The internal resistance `r` of the battery is `30 Omega`

D

The internal resistance `r` of the battery is `5 Omega`

Text Solution

Verified by Experts

The correct Answer is:
B, C
The potential measures the exact value of emf of a battery.
Therefore, `E = 1.55 V`.
Also, `1.4=I(280)` or `I=0.005 A`
Also, `1.4 = I(280)`or `I = 0.005 A`
Also, `V = E - Ir` or `r = ((E - V))/(I) = (1.55 - 1.40)/(0.005) = 30 Omega`
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Knowledge Check

  • An ammeter is connected in series with an unknown resistance and a voltmeter is connected across the terminals of the resistance . If the ammeter reads 1.2 A and the voltmeter reads 18 V the n value of the resistance is

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    `21 . 6`
    B
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    A
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    B
    `20 Omega`
    C
    `30 Omega`
    D
    `40 Omega`

  • A voltmeter having a resistance of 1800 Omega employed to measure the potential difference across a 200 Omega resistor which is connected to the terminals of a dc power supply having an emf of 50 V and an internal resistance of 20 Omega . What is the percentage decrease in the potential difference across the 200 Omega resistor as a result of connecting the voltmeter across it?

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    B
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