Light Summary Class 7 NCERT Summary Chapter 13

What is light?

• It is a natural agent which stimulates sight and makes things visible.
• It travels in a straight line.
• It is a form of energy.

What is an image?

• It is an impression of the object created by the light on the mirror.
• Distance between image and mirror and, the object and mirror is always same.

Types of image

• Erect image: When the image is formed the same side up as that the object.
• Inverted image: When image is formed upside-down compared to object.

If we increase or decrease the distance between the object and the mirror then the distance between the image and the mirror are also increase or decrease.

Left-right inversion of image

• Image formed by the mirror is always left-right inverted which means the right side of the object appears as the left side of image and the left side of the object appears at the right side of the image.

Reflection of light

• Incident ray: The ray which falls on the reflecting surface is called an incident ray.
• Reflected ray: The ray that gets reflected back from the reflecting surface is called reflected ray.

Laws of reflection of light
There are two laws for reflection of light. They are:

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

Spherical mirrors

• This mirror has a sphere like shape.
• Two types of spherical mirrors are:
  (i) Concave mirror: It is a type of spherical mirror whose reflecting surface is curved inwards.
  (ii) Convex mirror: It is a type of spherical mirror whose reflecting surface is curved outwards.

Also, there are two types of images formed by the spherical mirrors. They are:

(i) Real image: It is formed when the light rays reflect and meet at the same point.
(ii) Virtual image: The image formed when light rays reflect and diverge from the same point.

Lenses

• It is a part of reflecting material like glass or plastic but curved from both sides.
• Lenses are unlike mirrors that have a reflecting surface only on one side.

Types of lenses

• Convex lens: It is curved outwards and it is thicker at the center and narrows down at the edges. It merges the light rays passing through it.
• Concave lens: It is curved inwards and it has wider edges and thinner centre. It reflects the light back that travel through it in different directions.

Rainbow

• It is a natural phenomenon in which light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
• It contains seven colours: Red, orange, yellow, green, blue, indigo and violet.