A telescope consisting of an objective of focal length 60 cm and a single eye lens of focal length 20 cm is focused on a distant object in such a way that parallel rays comes out from the eye lens. If the object subtends at angle of 1° at objective, the angular width of image is

Question

A telescope consisting of an objective of focal length 60 cm and a single eye lens of focal length 20 cm is focused on a distant object in such a way that parallel rays comes out from the eye lens. If the object subtends at angle of 1° at objective, the angular width of image is (A) 1° (B) 2° (C) 3° (D) 4°

Tardigrade Admin · Accepted Answer

m=(θ/θ0)=(f0/fe) ⇒ θ=1° × (60/20)=3°

Q. A telescope consisting of an objective of focal length $60 c m$ and a single eye lens of focal length $20 c m$ is focused on a distant object in such a way that parallel rays comes out from the eye lens. If the object subtends at angle of $1^{\circ}$ at objective, the angular width of image is

$1^{\circ}$

$2^{\circ}$

$3^{\circ}$

$4^{\circ}$

$m = \frac{θ}{θ _{0}} = \frac{f _{0}}{f _{e}}$
$\Rightarrow θ = 1^{\circ} \times \frac{60}{20} = 3^{\circ}$

Q. A telescope consisting of an objective of focal length 60cm and a single eye lens of focal length 20cm is focused on a distant object in such a way that parallel rays comes out from the eye lens. If the object subtends at angle of 1∘ at objective, the angular width of image is

1∘

2∘

3∘

4∘