Electrical Methods

Step 1: Understand cripping error.
Cripping error is a phenomenon in energy meters where the disc comes to rest prematurely due to hysteresis losses in the iron core, leading to inaccurate readings.
Step 2: Preventing cripping error.
To reduce this error, the discs must be laminated to minimize eddy current losses and reduce hysteresis in the magnetic field.
Step 3: Conclusion.
Thus, the discs must be laminated to avoid cripping error, corresponding to option (A).

Step 1: Understanding the principle.
In a gravity-controlled instrument, the deflection of the needle depends on the current. The deflection angle is proportional to the sine of the deflection angle, which causes the scale to be crowded.
Step 2: Conclusion.
Thus, the current is proportional to the sine of the deflection angle, corresponding to option (D).

Step 1: Use the formula for capacitive reactance.
The capacitive reactance is given by the formula: where is the frequency and is the capacitance.
Step 2: Extract the frequency from the current equation.
The current equation is , so the frequency is:
Step 3: Calculate the capacitive reactance.
Substitute and :
Step 4: Conclusion.
Thus, the capacitive reactance is 318.31 ohms, which corresponds to option (A).