- If a ray of light from the object appears to diverge from the principal focus located on the same side of the lens, then it should pass through concave lens after refraction.
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Refraction through Curved Surface:
A lens is a portion of a transparent refracting medium bounded by two spherical surfaces. Because the lenses are made from spheres, they are called as spherical lenses. They are mainly of two types :
- Convex lens
- Concave lens
- A convex lens is thick in middle and thin at the rim. It makes the parallel rays of light to converge and come to a point. Hence, it is also called a converging lens.
- A concave lens is thin in the middle and thick at rim. It makes the parallel rays of light to spread from a point. Hence it is also called a diverging lens.
- The point at which the incident rays parallel to principal axis will converge upon after refraction in a convex lens is called its principal focus. Where as in a concave lens the point from where incident rays parallel to the principal axis of the lens appear to be coming, is called as its principal focus (F).
- A ray of light from the object, parallel to the principal axis, after refraction from a convex lens, passes through the principal focus on the other side of the lens. In case of a concave lens, the ray appears to diverge from the principal focus located on the same side of the lens.
- This is the reason why air bubble in water would act as a diverging lens as the index of refraction of air is less than that of water.
- The ability of a medium to refract light is also expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density.
- A ray of light travelling from a rarer medium to a denser medium slows down and bends towards the normal. When it travels from a denser medium to a rarer medium, it speeds up and bends away from the normal.