Introduction
when a ray of light travelling in one medium enters another medium of different optical density.
Refraction of Light
when a ray of light is incident on the boundary separating the two media having different densities.
Laws of Refraction
The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane.
Refraction of Light through a Glass Slab
When a ray light is passing from air to glass, that is, from a rarer medium to a denser medium, the refracted ray bends towards the normal drawn at the point of incidence.
Verification of Laws of Refraction - An Alternate Method
The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane.
Lenses
A lens is a portion of a transparent refracting medium bounded by two surfaces which are generally spherical or cylindrical or one curved and one plane surface.
Terminology Used in Optics
The focal length of a convex lens is always positive and that of a concave lens in always negative.
Formation of Image by a Convex Lens
When an object is placed in front of a lens, light rays coming from the object fall on the lens and get refracted.
Formation of Image by a Concave Lens
An incident ray of light coming from the object parallel to the principal axis of a concave lens after refraction appears to come from its focus.
Sign Convention for Lenses
The distances measured in the direction of incident rays are positive and all the distances measured in the direction opposite to that of the incident rays are negative.
Lens Formula
The values of the known parameters should be used with their proper sign as per the sign convention.
Magnification
As per sign convention for lenses, the height of an inverted and real image is negative and hence the magnification of a lens is negative when it produces an inverted and real image.
Power of a Lens
Whenever a ray of light passes through a lens (except when it passes through the optical centre) it bends.
Summary
The change of direction suffered by a ray of light as it passes obliquely from one medium to another is known as refraction.
Question and Answers
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Multiple Choice Questions
