Light Class 8 Notes - Chapter 16

The world as we know is largely known through senses and the sense of sight is one of the most important senses. It is only when the light from an object enters our eyes that we see it. The light might have been either emitted by the object or reflected by it. Some of the important terminologies related to light are:

  • Incident Ray – The ray of light that strikes a surface is known as an incident ray.
  • Reflected Ray – The ray that comes back from the surface after reflection is known as a reflected ray.
  • Normal – The point at which the incident ray strikes the surface is known as normal and a normal ray is incident to the surface at 90° degrees.
  • Angle of Incidence – The angle between the incident ray and the normal
  • Angle of Reflection – The angle between the reflected ray and the normal

Laws of Reflection

The two laws of reflection are :

  1. The angle of incidence is always equal to the angle of reflection.
  2. The incident ray, the normal at the point of incidence and the reflected ray all lie
    in the same plane.

Regular and Diffused Reflection

Diffused Reflection– When the parallel rays reflected from a rough surface are not parallel, the reflection is known as diffused reflection.

Regular Reflection – Reflection from a smooth surface like a mirror is known as regular reflection.

Human Eyes

We see things through the eyes when the reflected light from objects enters the eyes. The structure of the eye is listed below:

  • The eye is roughly in the spherical shape. The transparent front part of the eye is known as the cornea.
  • The dark muscular structure behind the eye is known as the iris. In the iris, a small opening known as the pupil is present and the size of the pupil is controlled by the iris. Iris controls the amount of light entering the eye.
  • The light is focussed on the back of the eye, on a layer called retina. The retina contains several nerve cells and the sensation felt by these nerve cells are transmitted to the brain through the optic nerve. The two types of cells in the retina are
    • a) Cones
    • b) Rods

Chapter 16 Light Class 8 Questions

  1. State the laws of reflection.
  2. Draw a labelled sketch of the human eye.
  3. Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Learn more about the light and its various properties and other related topics including class 8 science notes, at BYJU’S.

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Practise This Question

Choose the correct set of effects of adrenaline hormone from the following list:

i.  Faster heart beat

ii. Regular heart beat

iii. Increased alertness

iv. Faster breathing