refraction through glass slab | refraction experiment

Refraction of light

Hi, this blog is a practical part of refraction through glass slab.

To perform this experiment I have used a thick glass slab mounted on bottle caps and powerful laser as a light source.

We know that light emitted from laser travels in a straight path but when it passes through glass slab it bends.

This bending of laser beam when it travels from one transparent medium to other is known as refraction of light. The bending is caused due to the differences in density between the two substances / medium.

When the laser beam falls perpendicular to glass slab, the angle of incidence is 0°, so light travels in a straight line as usual.

Refraction through glass slab

When i change the direction of laser beam, the angle of incidence increases and we observe bending of light in glass slab.

Refraction of light


Light when travels from rarer to denser medium, it’s speed decreases. The decrease in speed indicates the reduction in energy carried by the light wave.

The speed of light in air is approximately 3 lakh Km/Sec and in glass it travels at a slower speed of 2 lakh Km/Sec.

Have a look on the diagram of refraction through glass slab

Refraction through glass slab


Incident ray : The ray of light that falls obliquely on the surface of glass slab is known as incident ray.

In other words the path by which light enters the glass slab is known as incident ray and the angle between incident ray and surface is known as incident angle.

Refracted ray : The path of light inside the glass slab is known as refracted ray and the angle between refracted ray and normal is known as angle of refraction.

Emergent ray : The path by which light emerges out is known as emergent ray and the angle made by emergent ray to the surface is known as angle of emergence.

Laws of refraction

The laws of refraction are –

  1. The incident ray, the normal and the refracted ray, lie in the same plane.
  2. The ratio of sine angle of incidence and sine angle of refraction is constant. This law is known as Snell’s law.

Disclaimer :

  1. Glass has very sharp edges it can cut your skin very easily. Make sure the edge of slab is smooth and polished.
  2. The laser used in this experiment is very powerful. Wear eye protecting goggles and ensure the laser beam should not point to your eyes.


Akash Sharma

Watch this experiment video

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