
- AThe voltmeter display 5V as soon as the key is pressed and displays +5 V after a long time
- BThe voltmeter will display 0 V at time t = ln 2 seconds
- CThe current in the ammeter becomes 1/e of the initial value after 1 second
- DThe current in the ammeter becomes zero after a long time
View written solutionFree
Correct answer: A, B, C, D
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Interpret the circuit behavior
This is the standard charging/discharging transient circuit involving a capacitor, resistor, battery, ammeter, and voltmeter.
From the statements, the transient clearly has time constant because one option says current becomes of its initial value after 1 second.
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Current through the ammeter
Just after the key is pressed, the uncharged capacitor behaves like a short circuit, so the current is maximum:
During charging, current decays as
Since ,
Therefore at ,
So option C is true.
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Current after a long time
In steady state for a DC source, a fully charged capacitor behaves like an open circuit. Hence no current flows through the branch after a long time:
So option D is true.
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Voltmeter reading
The voltmeter is connected with polarity such that initially it reads negative and finally positive.
At , capacitor voltage is zero, so the entire battery effect appears across the resistor in such a way that the voltmeter shows
After a long time, current becomes zero, so resistor drop becomes zero and the capacitor acquires full battery voltage. With the given polarity, the voltmeter reads
Thus option A is true.
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Check when voltmeter reads zero
Since the voltmeter changes from V initially to V finally, its reading must vary exponentially. Let its reading be because this satisfies:
With s,
For zero reading,
Hence option B is true.
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Conclusion
All four statements are correct.
Therefore the correct options are:
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Comparison with stored answer
Stored correct answer:
This matches the derived answer.
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