It's commonly referred to as an electric current.
If the distance between two charges is halved, the electrical force between them increases by a factor 4.
In fact, the magnitude of the electric force between two charges is given by:

where
k is the Coulomb's constant
q1 and q2 are the two charges
r is the separation between the two charges
We see that the magnitude of the force F is inversely proportional to the square of the distance r. Therefore, if the radius is halved:

the magnitude of the force changes as follows:

so, the force increases by a factor 4.
Answer:
(a). Index of refraction are
= 1.344 &
= 1.406
(b). The velocity of red light in the glass
2.23 ×
The velocity of violet light in the glass
2.13 ×
Explanation:
We know that
Law of reflection is

Here
= angle of incidence
= angle of refraction
(a). For red light
1 ×
=
× 
= 1.344
For violet light
1 ×
=
× 
= 1.406
(b). Index of refraction is given by

= 1.344


2.23 ×
This is the velocity of red light in the glass.
The velocity of violet light in the glass is given by

2.13 ×
This is the velocity of violet light in the glass.