Ncert Exercises & Solutions

For an L-C-R circuit, the power transferred from the driving source to the driven oscillator is $P = I^{2} Zcosϕ$ .

a.	Here, the power factor cosϕ ≥ 0 , P ≥ 0 .
b.	The driving force can give no energy to the oscillator (P = 0) in some cases.
c.	The driving force cannot syphon out (P<0) the energy out of the oscillator.
d.	The driving force can take away energy out of the oscillator.

1. (a, b, c)
2. (a, c, d)
3. (b, c, d)
4. (c, d)

(1) Hint: The power factor depends on the impedance of the circuit.

Step 1: According to the question power transferred,

P = I^{2} Z \cos φ

Where I is the current, Z = Impedance and cos

φ

is the power factor.

As power factor,

cosφ = \frac{R}{Z}

Where

R > 0 and Z > 0

\Rightarrow cosφ > 0 \Rightarrow P > 0