Light – Reflection and Refraction

A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Calculate the focal length of the mirror. [CBSE 2025]

The refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. Calculate the refractive index of glass with respect to water. [CBSE 2024]

Draw a ray diagram to show the formation of image of an object placed between F and 2F of a convex lens. State the nature, position and size of the image. [CBSE 2023]

An object 5 cm tall is placed 30 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image formed. [CBSE 2022]

State the laws of refraction of light. Explain why a ray of light bends when it travels from one medium to another. [CBSE 2021]

1/f = 1/v + 1/u where f = focal length, v = image distance, u = object distance

m = -v/u = h₂/h₁ m = magnification, h₂ = image height, h₁ = object height

1/f = 1/v - 1/u Sign convention: same as mirror formula

m = v/u = h₂/h₁

n = c/v = sin i/sin r n = refractive index, c = speed of light in vacuum, v = speed in medium

P = 1/f (in meters) Unit: Dioptre (D)

Using similar triangles from ray diagram: For object and image distances from pole: △ABC ~ △A'B'C AB/A'B' = CB/CB'

Using sign convention and algebraic manipulation: 1/f = 1/v + 1/u

For thin lens with refractive index n: 1/f = (n-1)(1/R₁ - 1/R₂) where R₁, R₂ are radii of curvature

At interface between two media: n₁ sin i = n₂ sin r Derived from principle of least time (Fermat's principle)