Question

For an LCR circuit, the power transferred from the driving source to the driven oscillator is P = I²Z cos ф.

Options

• Here, the power factor cos Φ ≥ 0, P ≥ 0.

• The driving force can give no energy to the oscillator (P = 0) in some cases.

• The driving force cannot syphon out (P < 0) the energy out of oscillator.

• The driving force can take away energy out of the oscillator.

Answer 1

Here, the power factor cos Φ ≥ 0, P ≥ 0, the driving force can give no energy to the oscillator (P = 0) in some cases and the driving force cannot syphon out (P < 0) the energy out of oscillator.

Explanation:

As per question P = I²Z cos Φ

Power factor cos Φ = \[\frac {R}{Z}\]

As R > 0 and Z > 0

If cos Φ ≥ 0, then from the expression P ≥ 0.

If Φ = 90°, then from the expression P = 0.

Since, R and Z both are positive, then cos ф cannot be negative. So, P cannot be negative.