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