Answer:

Explanation:
Electrostatic Forces
The force exerted between two point charges
and
separated a distance d is given by Coulomb's formula

The forces are attractive if the charges have different signs and repulsive if they have equal signs.
The problem described in the question locates three point charges in a straight line. The charges have the values shown below


The distance between
and
is

The distance between
and
is

We must find the value of
such that

Applying Coulomb's formula for
is

Now for 

If the total force on
is zero, both forces must be equal. Note that being q2 negative, the force on q3 is to the right. The force exerted by q1 must go to the left, thus q1 must be positive. Equating the forces we have:


Simplfying and solving for 



Explanation:
(a)
Critical angle is the angle at the angle of refraction is 90°. After the critical angle, no refraction takes place.
Using Snell's law as:
Where,
is the angle of incidence
is the angle of refraction = 90°
is the refractive index of the refraction medium
is the refractive index of the incidence medium
Thus,
The formula for the calculation of critical angle is:
Where,
is the critical angle
(b)
No it cannot occur. It only occur when the light ray bends away from the normal which means that when it travels from denser to rarer medium.
Answer:
Heterogeneous
Explanation:
A chemical substance is composed of one type of atom or molecule. A mixture is composed of different types of atoms or molecules that are not chemically bonded. A heterogeneous mixture is a mixture of two or more chemical substances where the various components can be visually distinguished.
I think it is <span>Alpha rays.</span>