Test: Refraction through Glass - UPSC MCQ

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. It's exact value is defined as 299 792 458 metres per second ( or approximately, 3*10⁸ m/s)

When a ray enters from glass to air medium, it bends away from the normal. This phenomenon is known as refraction. Here's a detailed explanation:

- Light rays change speed and direction when they pass from one medium to another with a different optical density.
- As light travels from glass (higher optical density) to air (lower optical density), it bends away from the normal (an imaginary line perpendicular to the surface).
- This bending of light is due to the change in speed of light in different mediums, causing the ray to deviate from its original path.

Therefore, the correct answer is B: It bends away from normal.

Light travels faster in substance X compared to substance Y, indicating the refractive index is greater for:
The refractive index (n) is inversely proportional to the speed of light in a substance.
If light travels faster in substance X, it means X has a lower refractive index than Y.
Therefore, the refractive index is greater for substance Y.
The correct answer is B: Substance-Y.

During refraction through a rectangular glass slab, the following points apply:

1. Angle of Incidence and Angle of Refraction at the First Surface:

   • When light enters the rectangular glass slab from air (or another medium), it bends towards the normal due to the higher refractive index of glass compared to air.
   • The angle of incidence (i₁​) at the first surface is always greater than the angle of refraction (r₁​).

2. Angle of Incidence and Angle of Refraction at the Second Surface:

   • As light exits the glass slab and enters back into air, it bends away from the normal because the refractive index of air is less than that of glass.
   • The angle of incidence (i₂​) at the second surface is equal to the angle of refraction (r_2​).

Summary:

• The angle of incidence is always greater than the angle of refraction at the first surface of the slab.
• The angle of incidence is equal to the angle of refraction at the second surface of the slab.

So, the correct option is: Option D

The speed of light in a medium can be calculated using the refractive index formula:

Refractive Index (n) = Speed of Light in Vacuum (c) / Speed of Light in Medium (v)
Given:
Refractive Index of Glass (n) = 1.50
Speed of Light in Vacuum (c) = 3 × 10⁸ m/s
Rearranging the formula to find v:
v = c / n
Substitute the values:
v = (3 × 10⁸ m/s) / 1.50
Calculating:
v = 2 × 10⁸ m/s
So, the correct answer is:
A: 2 × 10⁸ m/s

• Snell's law of refraction states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
• This law, also known as Snell's Law, describes how light behaves when it passes through different mediums.
• It helps us understand how light bends when it moves from one medium to another, based on their refractive indices.