All good conductors have high____________?

Instantaneous power in inductor is proportional to the

A. product of the instantaneous current and rate of change of current.
B. square of instantaneous current.
C. square of the rate of change of current.
D Temperature of the inductor.

The instantaneous voltage across the inductor is expressed as the product of inductance and rate of change of current through it. Power is expressed as the product of current and voltage. Hence instantaneous power in an inductor is proportional to the product of instantaneous current and rate of change of current through it.

Which of the followings is/are active element?

A. Voltage source
B. Current source
C. Both
D. None of these.

Active elements are capable of delivering energy independently for long time or ideally infinite time. Both voltage and current source are active element and they can change energy level of a circuit.

Capacitor does not allow the sudden change of ?

A. current
B. voltage
C. power
D. None of the above

The expression of current through a capacitor is
For sudden change of voltage infinite current is required. But practically it is not possible.
Practical capacitor circuit has finite value of time constant

The resistance of a conductor of diameter d and length l is R Ω. If the diameter of the conductor is halved and its length is doubled, the resistance will be

A. R Ω
B. 2R Ω
C. 4R Ω
D. 8R Ω

As per law of resistance, the resistance of the conductor is inversely proportional to its cross-sectional area i.e. it is inversely proportional to the square of the diameter of cross-sectional area of the conductor. As per same law of resistance, the resistance of the conductor is directly proportional to the length of the conductor.