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Rev. Notes > IGCSE > Light
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Nature of light

Important features of light

Reflection of light

Use of mirror (Periscope)

Refraction of light

Refractive index

Critical angle

Total internal reflection

Use of prism (Periscope)

Convex lens

Behavior of standard rays after passing through convex lens

Image formed by convex lens

Nature and position of image produced by convex lens

Principle of camera

Dispersion of light

Newton's experiment for dispersion of light

Improvement in Newton's experiment for dispersion of light

Recombination of colors


Reflection through plane mirror

Image through plane mirror

Test Yourself



Behavior of standard rays after passing through convex lens

Information about the images formed by a lens can be obtained by drawing any of two of the following standard rays from the top of the object.

Standard rays:

  • If a ray of light is coming parallel to the principal axis, after refracting through the convex lens it passes through the focus point or principal focus.
  • If ray of light is passing through the optical centre, after refracting through the convex lens, it goes straight wihout bending or deviating.
  • If a ray of light is coming from the focus point or principal focus, after refracting through convex lens, it becomes parallel to the principal axis.


Q: Why ray of light passing through the opticle centre of the convex lens does not bend?

The below diagram explains the fact.

The ray of light, which is approaching to the lens at opticle centre has angle of incidence 26o and angle of refraction 18o. When this ray of light is emerging out from the lens (glass) in the air, It is almost taking the same path which it had before entring the lens. you can see that at both boundries, refraction ophenomenon occcurs but ultimately th eray of light remains on the same path. 

Note: "The ray of light does not bend, when it passe through the opticle centre of the lens" is strictly true for thin lenses, while in thick lense you may have small deviation of the path of the incident ray and the emrging ray.

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