C is the first & the second question is A
<h2>Answer: True
</h2>
The <u>Doppler effect</u> refers to the change in a wave perceived frequency when the emitter of the waves, and the receiver (or observer in the case of light) move relative to each other.
In other words, it is the variation of the frequency of a wave due to the relative movement of the source of the wave with respect to its receiver.
It should be noted that this effect bears its name in honor of the Austrian physicist <u>Christian Andreas Doppler</u>, who in 1842 proposed the existence of this effect for the case of light in the stars. Another important aspect is that the effect occurs in all waves (including light and sound). However, it is more noticeable to humans with sound waves.
To calculate the force between two negative charges, we use the formula which is given by the Coulomb`s Law as
Here, 
and
are the charges on the pith balls, r is the separation between the charges and k is constant and its value is 
.
Given 
and 
.
Substituting these values in above formula we get,
Thus, the repulsive force between two pith balls is 
.
B)<span>Readily accept electron flow.</span>
