Answer :

AL2006

The frequency is    (40) / (20 seconds) = 2 per second = 2 Hz.

The period is  1/(frequency)  =  1 / (2 per second)  =  1/2 second .


PBCHEM

Answer : Time period will be 0.5 seconds.

Explanation : We can use the formula as;

f = c / λ

f = wave speed c (units m/s) / wavelength λ (units m).

Here, c = 40 and λ = 20;

f = 40 / 20 = 2 Hz

The formula for finding time period is:

[tex] T (period) = \frac{1}{f} [/tex] where f = frequency

We have, f = 2 Hz;

[tex] T (period)= \frac{1}{2} [/tex] = 0.5 second.

Therefore, time period will be 0.5 seconds.