Question

A telescope has an objective lens of focal length 200 cm and an eye piece with focal length 2 cm. If this
telescope is used to see a 50 m tall building at a distance of 2 km, what is the height of the image of the
building formed by the objective lens?
(2) 10 cm
(1) 5 cm
3) 1
(3) 1 cm
(4) 2 cm​

Answer 1

Answer:

Correct option is

A

5 cm

Given, u=−2000m,v=?,f=200cm=2m

From lens formula,

v

1

−

u

1

=

f

1

⇒

v

1

+

2000

1

=

2

1

v

1

=

2

1

−

2000

1

=

2000

1000−1

=

2000

999

v=

999

2000

Magnification,

u

v

=m=

999×2000

2000

=

999

1

Size of image =

999

1

×50×100cm≈5cm