Question

In an ac circuit, the instantaneous current is zero,when the instantaneous voltage is maximum. In this case, the source may be connected to :
A. pure inductor.
B. pure capacitor.
C. pure resistor.
D. combination of an inductor and capacitor.
Choose the correct answer from the options given below :

• A. A, B and C only
• B. B, C and D only
• C. A and B only
• D. A, B and D only

Answer 1

The Correct Option is D

Understanding the Phase Relationship in AC Circuits:
 In an AC circuit: For a pure inductor, the current \( I \) lags the voltage \( V \) by \( 90^\circ \) (or \(\(\frac{\pi}{2}\) \) radians).
For a pure capacitor, the current \( I \) leads the voltage \( V \) by \( 90^\circ \). For a pure resistor, the current and voltage are in phase, meaning that they reach zero and maximum values simultaneously.

Condition for Instantaneous Current to be Zero When Voltage is Maximum:
 The given condition (current is zero when voltage is maximum) implies a \( 90^\circ \) phase difference between the current and voltage.
This situation occurs in:
- A pure inductor, where current lags the voltage by \( 90^\circ \).
- A pure capacitor, where current leads the voltage by \( 90^\circ \).
- A combination of an inductor and capacitor (LC circuit), where the phase difference can also result in current being zero when voltage is maximum.

Conclusion:
Since this phase relationship is possible in a pure inductor, pure capacitor, or an LC combination, the correct answer is  Option (4): A, B, and D only.

Answer 2

Step 1: Understanding the given condition.
In the given AC circuit, the instantaneous current is zero when the instantaneous voltage is maximum.
This means that the current and voltage are out of phase by 90° (a quarter of a cycle).

Step 2: Recall phase relations for different AC elements.
- For a pure resistor, current and voltage are in phase. Hence, when voltage is maximum, current is also maximum.
- For a pure inductor, current lags the voltage by 90°. Therefore, when the voltage is maximum, the current is zero.
- For a pure capacitor, current leads the voltage by 90°. Therefore, when the voltage is maximum, the current is again zero.
- For a combination of L and C, if the circuit is tuned such that the voltage and current are 90° out of phase (non-resonant case), the instantaneous current can still be zero when voltage is maximum.

Step 3: Analyze the condition.
Since the given condition (current = 0 when voltage = maximum) occurs when the current and voltage are 90° out of phase, this can happen in:
- A pure inductor
- A pure capacitor
- A non-resonant combination of inductor and capacitor

Step 4: Exclude the incorrect case.
A pure resistor cannot satisfy the given condition because current and voltage are in phase.

Step 5: Final Answer.
The correct cases are:
A, B, and D only

Final Answer:
\[ \boxed{A, B \text{ and } D \text{ only}} \]