#### Question

If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?

#### Solution

Height of the tower, *h*_{1} = 100 m

Distance of the tower (object) from the telescope, *u* = 3 km = 3000 m

The angle subtended by the tower at the telescope is given as:

`theta = h_1/u`

`= 100/3000 = 1/30 rad`

The angle subtended by the image produced by the objective lens is given as:

`theta = h_2/f_o = h_2/140 rad`

Where,

*h*_{2} = Height of the image of the tower formed by the objective lens

`1/30 = h_2/140`

`:. h_2 = 140/30 = 4.7`

Therefore, the objective lens forms a 4.7 cm tall image of the tower.

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Solution If this Telescope is Used to View a 100 M Tall Tower 3 Km Away, What is the Height of the Image of the Tower Formed by the Objective Lens? Concept: Optical Instruments - Telescope.