Revision: Term - 3 >> Light Science SSLC (English Medium) Class 7 Tamil Nadu Board of Secondary Education

The light traveling in any one direction in a straight line is called a ray of light.

A group of light rays given out from a source is called a beam of light

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

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

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.

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

The refractive index of a medium is defined as the ratio of the speed of light in vacuum (or air) to the speed of light in that medium.

Materials that are not able to allow light to pass through, are called opaque material.

Materials that allow light to pass through completely are known as transparent materials.

INCIDENT RAY AB: The ray light AB which is in air strikes the glass slab at B.
Or
“A ray of light falling on the surface separating the two media.”
REFRACTED RAY BK: A ray of light which after passing the first medium is in second medium i.e. ray BK.
“A ray of light travelling in other medium in the changed direction.”
ANGLE OF INCIDENCE: “The angle which the incident ray makes with the normal is called angle of incidence.”
i.e. ∠i
ANGLE OF REFRACTION: “The angle which the refracted ray makes with the normal is called angle of refraction.”
i.e. ∠r

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

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.

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’.

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.

• 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.

• Refractive index (µ) = c / V, where c is the speed of light in vacuum and V is the speed in the medium.
• The refractive index of a medium is always > 1 because the speed of light in any medium is less than in a vacuum.
• If µ₁ = µ₂ or the angle of incidence = 0°, the ray of light passes undeviated.
• Wavelength in medium A′ = A / µ; wavelength decreases in denser medium and increases in rarer medium.
• Refractive index decreases with decreasing speed of light, and is maximum for violet light and minimum for red light.

• 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.