Light: reflection and refraction · प्रकाश: परावर्तन और अपवर्तन
A free Physics lesson for Class 10 children.
A concave mirror curves inwards. Parallel rays reflect through its focus, so it is used in torches and by dentists.
A convex mirror curves outwards. It gives a small, erect image and a wide view, so it is used as a rear-view mirror.
The mirror formula is 1/v + 1/u = 1/f, and the magnification is m = −v/u.
Light bends when it passes from one medium to another. This is refraction.
Light bends towards the normal on entering a denser medium, and away from the normal on entering a rarer one.
The refractive index of a medium is n = c/v, the speed of light in air divided by its speed in the medium.
A convex lens converges rays. A concave lens diverges them.
The power of a lens is P = 1/f, with f in metres, measured in dioptres.