Refraction

Through Lens

Refraction of parallel ray:

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

Fig: Ray parallel to principal axis

Fig: Ray parallel to principal axis

Refraction of ray passing through the Principal 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.

Fig: Ray passing through focus

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:

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.

Fig: Ray passing through O

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: 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.

Fig: Converging Lens

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.

Fig: Diverging Lens