Class 7 Science


Learning Goals

Light is a form of energy. We are able to see the world around us because of light. You cannot see an object in complete darkness because there is not light to bounce back from the object.

Propagation of Light

linear propagation of light

Light always travels in a straight line. The following experiment proves that light always travels in a straight line. When the candle is viewed through a straight tube, its flame can be seen. In case of a bent tube, the flame cannot be seen.

Reflection of Light

When light falls on a shiny surface, it bounces back. This phenomenon is called reflection. We are able to see images in mirrors or in water, because of reflection.

reflection of light

Laws of Reflection

There are two laws of reflection.

  1. The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
  2. Angle of incident and angle of reflection are equal.

Whenever an image is formed by a mirror or by any reflecting surface; the laws of reflection are obeyed.

Real Image: When the image can be obtained on a screen, it is called real image. Real image is formed in front of mirror. Images formed on the retina are real images. Images formed on the film of a camera are real images.

Virtual Image: When the image cannot be obtained on a screen, it is called virtual image. Virtual image is formed behind the mirror.

Image formation in Plane Mirror

Image is of the same size as object. The distance of image and object from the plane mirror is same. Image is erect and virtual.

Lateral Inversion in Plane Mirror

A plane mirror makes laterally inverted image. This is the reason, your right hand looks like the left hand of your image. The word ‘AMBULANCE’ is written in laterally inverted form on the front of the ambulance. This is deliberately done so that the driver in a vehicle ahead can easily spot the ambulance and can give way.

Review Questions

What is light?

Answer: Light is a form of energy which helps us in getting the vision.

What is normal to the point of incidence?

Answer: The perpendicular to the surface at the point at which the incidence ray falls is called normal.