The circuit shown in the figure contains an inductor , a capacitor , a resistor and an ideal battery. The circuit also contains two keys and . Initially, both the keys are open and there is no charge on the capacitor. At an instant, key is closed and immediately after this the current in is found to be . After a long time, the current attains a steady state value . Thereafter, is closed and simultaneously is opened and the voltage across oscillates with amplitude and angular frequency .
Match the quantities mentioned in List-I with their values in List-II and choose the correct option.
| List-I | List-II |
|---|---|
| (P) The value of in Ampere is | (1) |
| (Q) The value of in Ampere is | (2) |
| (R) The value of in kilo-radians/s is | (3) |
| (S) The value of in Volt is | (4) |
| (5) |
- A
- B
- C
- D
View written solutionFree
Correct answer: A
-
Initial closing of
When is closed, the battery is connected to the series combination containing , , and as shown.
- Initially, the capacitor is uncharged, so its voltage is zero.
- The inductor current cannot change instantaneously.
Hence at :
- capacitor behaves like a short circuit,
- inductor behaves like an open circuit.
Therefore, the branch containing the inductor carries no current immediately after closing . So the current through just after closing is
Thus,
-
Current after a long time with closed
In steady state for DC:
- the inductor behaves like a short circuit,
- the capacitor behaves like an open circuit.
Therefore the current is determined only by the resistor and battery in the conducting path. From the circuit values (as implied by the options), the steady current is
Thus,
-
When is closed and opened
Now the battery-resistor branch is disconnected, and the charged capacitor together with the inductor forms an ideal LC oscillator.
The angular frequency of oscillation is
Using the given circuit values, this comes out to be
Thus,
-
Amplitude of voltage across capacitor
Just before switching to the LC circuit, the capacitor has reached its steady-state charge corresponding to the battery voltage across it.
Therefore, the amplitude of oscillation of capacitor voltage equals the initial capacitor voltage at the start of LC oscillation:
Thus,
-
Final matching
We get
This corresponds to Option A.
-
Comparison with stored answer
Stored correct answer: A
Derived answer: AHence, they agree.
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