Question 318: Ray Optics

Question

A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the  objective, the lenses must be separated by a distance

Accepted Answer

Given: Focal length of objective, f
0
= 40cm
Focal length of eyeÃ¢ÂÂpiece f
e
= 4 cm
image distance, u
0
= 200 cm
Using lens formula for objective lens
$${1 \over {{v_0}}} - {1 \over {{u_0}}} = {1 \over {{f_0}}}$$
$${1 \over {{v_0}}} - {1 \over { - 200}} = {1 \over {40}}$$
$$ \Rightarrow $$ $${1 \over {{v_0}}} = {1 \over {40}} - {1 \over {200}}$$ = $${4 \over {200}}$$
$$ \Rightarrow $$ v
0
= 50 cm
Tube length($$l$$) = Distance between lenses = v
o
+ f
e
= 50 + 4 = 54 cm

Answer

50.0 cm

Answer

54.0 cm

Answer

37.3 cm

Answer

46.0 cm

Ray Optics

A astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance

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