Light Reflection and Refraction

What will you learn

• Light seems to travel in straight lines.

• Mirrors and lenses form images of objects. Images can be either real or virtual, depending on the position of the object.

• The reflecting surfaces, of all types, obey the laws of reflection. The refracting surfaces obey the laws of refraction.

• The focal length of a spherical mirror is equal to half its radius of curvature.

• The magnification produced by a spherical mirror is the ratio of the height of the image to the height of the object.

• A light ray travelling obliquely from a denser medium to a rarer medium bends away from the normal. A light ray bends towards the normal when it travels obliquely from a rarer to a denser medium.

• Light travels in vacuum with an enormous speed of 3×108 m s-1. The speed of light is different in different media.

• The refractive index of a transparent medium is the ratio of the speed of light in vacuum to that in the medium.

• In case of a rectangular glass slab, the refraction takes place at both air-glass interface and glass-air interface. The emergent ray is parallel to the direction of incident ray.

• Power of a lens is the reciprocal of its focal length. The SI unit of power of a lens is dioptre.