Use the concept of beat frequency to find the applicable final freqeuncy for 20Hz beat frequency.
Beat can be defined as 'the interference pattern between two sounds of slightly different frequencies0
The expression for beat frequency is given as

Where,
Final frequency
Initial frequency
The beat frequency for us is 25Hz and the initial frequency is 240Hz, then

Being an absolute value, two values are possible, both in addition and subtraction:

The two possible values are


Answer:
0.159 Tesla per second
Explanation:
r = 2 m, e = 2 V,
Let the rate of magnetic field changing is dB / dt.
By use of Farady's law of electromagnetic induction
e = rate of change of magnetic flux
e = dФ /dt
e = A x dB / dt
2 = 3.14 x 2 x 2 x dB / dt
dB / dt = 0.159 Tesla per second
The correct answer is
(1) speed
In fact, the speed of an electromagnetic wave does not depend on the type of wave, but only on the medium: since both the waves are travelling in vacuum (same medium), they are travelling at same speed, which corresponds to the speed of light in vacuum:
