Ans. TELESCOPE
An optical instrument which is used to observer distant objects using lenses or mirrors is called telescope.
Refracting Telescope
A telescope that uses two converging lenses is called refracting telescope.
Working of Refracting Telescope
The ray diagram of refracting telescope is shown in the figure. When parallel rays from a point on a distant object pass through objective, a real image I-i is formed at the focus F0 of the objective lens. This image acts as an object for the eyepiece. A large virtual image I2 of Ij is formed by the eyepiece at large distance from the objective lens. This virtual image makes an angle 6 at the eye.