Question

The ratio of skin depth in copper at 1 kHz to that at 100 MHz is approximately :
(A) 3
(B) 30
(C) 300
(D) 3000

Answer 1

Skin depth δ is given by formula

$$\delta= \sqrt{\frac {\rho}{\pi f \mu}} (1)$$

where ρ is the resistivity of material, f is the frequency, μ is the permeability

Using (1) we got:

$$\frac {\delta_1}{\delta_2}=\sqrt{\frac {f_2}{f_1}} (2)$$

In this case, we have

$$\frac {\delta_1}{\delta_2}=316$$

Answer:

(C) 300