Revision: Light Science Secondary School (English Medium) (5 to 8) Class 8 CBSE

Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

The bouncing of light by any smooth or polished surface is called.

The phenomenon due to which a parallel beam of light traveling through a certain medium, on striking some polished surface, bounces off from it, as a parallel beam, in some other direction, is called regular reflection.

The phenomenon of bouncing back of light rays in the same medium on striking a surface is called reflection of light.

The principal axis is the straight line passing through the pole and the centre of curvature.

Incident ray- The ray of light that falls on the surface of the reflection materials.

Angle of incidence: The angle formed between the incident ray PO and the normal ‘ON’ is angle of incidence.

Reflected ray: The ray of light that comes from the point when the incident ray falls on the reflection material.

Normal: The perpendicular line drawn from, the point of incidence to the plane of reflecting surface is called normal.

A prism is a transparent medium bounded by five plane surfaces with a triangular cross-section.

The phenomenon of the splitting of white light by a prism into its constituent colours is known as dispersion of light.

When a beam of white light or composite light is refracted through any transparent media such as glass or water, it is split into its component colours. This phenomenon is called ‘dispersion of light’.

The phenomenon of splitting of white light by a prism into its constituent colours is known as dispersion.

OR

The splitting of light into its component colours is called dispersion.

OR

The process of separation of light into its component colours while passing through a medium is called the dispersion of light.

OR

The phenomenon in which white light splits into its constituent colours when it passes through a prism or another medium is called dispersion of light.

The angular separation between the two extreme rays of a dispersed beam of light is called angular dispersion.

On passing white light through a prism, the band of colours seen on a screen is called the spectrum.

or

The band of the coloured components of a light beam is called its spectrum.

n = \[\frac {360°}{θ}\]

• If n is even → N = n − 1
• If n is odd → N = n (object not on bisector); N = n − 1 (object on bisector)
• If n is a fraction → N = integral part of n

• The angle of incidence ∠i = angle of reflection ∠r.
• The incident ray, reflected ray, and normal lie in one plane; both rays are on either side of the normal.

• Reflection occurs when light bounces off a smooth surface like a mirror, following fixed laws.
• Plane mirrors always form virtual, erect, and same-sized images that are laterally inverted.
• Curved surfaces (like a spoon) act as spherical mirrors, changing the image size and orientation depending on the object's position.

• Dispersion is the splitting of white light into seven colours (VIBGYOR) when it passes through a prism or similar transparent medium.
• Human eyes can detect light with wavelengths ranging from 400 nm (violet) to 700 nm (red).
• Different colours travel at different speeds in a medium like glass, so each colour has a different refractive index.
• Violet light bends the most, and red light bends the least, as it passes through a prism, producing a spectrum.
• A rainbow is formed due to dispersion, refraction, and internal reflection of sunlight by raindrops acting as tiny prisms.