Question

As the beam enters the medium, it will
$A.$ Diverge
$B.$ Converge
$C.$ Diverge near the axis and converge near the periphery
$D.$ Travel as a cylindrical beam

Answer 1

Hint: We will use the concept of refractive index and speed of light in different media. We know that when a beam of light enters a denser medium from the rarer medium then it will converge and vice versa. It means that denser medium has higher value of absolute refractive index and rarer medium has lesser value of refractive index.

Complete step by step answer:
We know that when a beam of light enters one medium to another then it bends from its original path which is known as refraction. In the question above, the first medium is not mentioned. So, we consider the first medium as vacuum.
We know that when a ray of light enters the other medium from vacuum then it will converge because the other medium acts as the denser medium and vacuum as a rarer medium. Beams of light will converge according to the given information.

So, the correct answer is “Option A”.

Additional Information:
Refraction occurs due to the fact that speed of light is different at different media. Like reflection, refraction also has two laws. Laws of refraction are as follows:-
$(i)$ Snell's Law : When a light ray is incident on a surface separating two transparent media, the ray bends at the time of changing the medium will be given by
$\dfrac{\sin i}{\sin r}=\dfrac{{{v}_{1}}}{{{v}_{2}}}=\dfrac{{{\mu }_{2}}}{{{\mu }_{1}}}$
Where, $i$ is angle of incidence, $r$ is angle of refraction, ${{v}_{1}}$ is the speed of light in first medium, ${{v}_{2}}$ is the speed of light in second medium, ${{\mu }_{1}}$ is the refractive index of the first medium and ${{\mu }_{2}}$ is the refractive index of second medium.
$(ii)$ The incident ray, the normal and the refracted ray at the interface all lie in the same plane.

Note: We have solved this problem by the assumption that light enters from vacuum to any medium as no other information is provided. Always remember that medium with higher refractive index has low speed and medium with lower refractive index has higher speed. Never be confused between the facts that when a light ray enters the denser medium from a rarer medium, it bends towards normal and when a light ray enters a rarer medium from a denser medium, it moves away from the normal.