What are the units of the coefficient of friction?
a. n
c. n²
b. 1/n
d. the coefficient of friction has no units.

The coefficient of friction has no units.

Option D

Explanation:

The coefficient of friction, just a measure of the relationship between normal forces when two bodies are in contact. It is a ratio-like quantity, where the numerator and the denominator are of same units. The coefficient of friction is a scalar.  

This is used to determine the frictional forces acting on the body, in physics. It is simply, the tangent of the angle of friction, and hence, has no units. Coefficient of friction reduces the object's speed, or supports to change the state of an object. It acts, only when the surface which is in contact with the body, is rough.

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.