Class 10 Science


Refraction of Light through Lens

When a ray of light is refracted by a spherical lens, there are many possibilities of behaviour by refracted ray. The path of refracted ray depends on the point of incidence on the given lens.

These notes are based on the chapter Light: Reflection and Refraction from class 10 science NCERT book and CBSE syllabus

  • Ray parallel to principal axis
  • Ray passing through principal focus
  • Ray passing through optical centre
  • Converging lens and diverging lens

The incident ray can be parallel to the principal axis, it may pass through F or through O. The reflected ray behaves differently in different situations.

Refraction of parallel ray

ray parallel to principal axis convex lens

Fig: Ray parallel to principal axis

When ray, that is parallel to the principal axis passes through a convex lens, it converges at focus of the convex lens.

ray parallel to principal axis concave lens

Fig: Ray parallel to principal axis

When the same ray passes through a concave lens, it diverges from the focus of a concave lens. The following figures show rays of light parallel to the principal axis passing through a convex lens and a concave lens.

Refraction of ray passing through the Principal focus

ray through focus convex lens

Fig: Ray passing through focus

When a ray passing through the principal focus passes through a convex lens, it emerges parallel to the principal axis of the convex lens. The following figure shows a ray of light passing through the focus of a convex lens.

ray through focus concave lens

Fig: Ray passing through focus

When a ray passing through the principal passes through a concave lens, it emerges parallel to the principal axis of the concave lens. This figure shows a ray of light passing through the focus of a concave lens.

Ray passing through the optical centre of lens

ray passing through optical centre convex lens

Fig: Ray passing through O

When a ray passing through the optical centre of a lens, it experiences no deviation in its path. This happens both in cases of convex and concave lenses. The following figure shows a ray of light passing through optical centre of a convex lens.

ray passing through optical centre concave lens

Fig: Ray passing through O

This figure shows a ray of light passing through optical centre of a concave lens. You can observe that there is no deviation in its path.

Converging lens

converging lens

Fig: Converging Lens

A convex lens is known as converging lens. Let us see the reason behind this. When rays of light parallel to the principal axis pass through a convex lens, all of them converge at the focus of the lens. Due to this, a convex lens is called a converging lens. Due to this property of a convex lens, you can use it to burn a peace of paper by using the sunlight. Sunlight gets concentrated at focus after it passes through a convex lens. This helps in increasing the heat which results in igniting the paper.

Diverging lens

diverging lens

Fig: Diverging Lens

A concave lens is known as diverging lens. Let us see the reason behind this. When rays of light parallel to principal axis pass through a concave lens, all of them appear to be diverging from the focus. Due to this, a concave lens is called a diverging lens.


More from this Lesson