An astronomical telescope has a length of 44 cm and tenfold

Home » Optics » Ray Optics and Optical Instruments » Question

An astronomical telescope has a length of 44 cm and tenfold magnification. The focal length of the objective lens is

1. 4 cm
2. 40 cm
3. 44 cm
4. 440 cm

Correct Option: B

Given : Length of astronomical telescope (f₀ + f_e) = 44 cm and magnification

	ƒ₀		= 10
	ƒ_e

From the given magnification, we find that ƒ₀ = 10f_e. Therefore, 10f_e + f_e = 44 or 11f_e = 44 or f_e = 4.
And focal length of the objective (f₀) = 44 – f_e = 44 – 4 = 40 cm.