In compound microscope final image formed at 25 cm from eyepiece lens. length of tube is 20cm. given that f_0 =1cm, find focal length of eye piece lens
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Answered by
1
Magnification, of compound microscope
m=m
0
×m
e
=(
f
0
L
×
f
e
D
)
Here, L = 20 cm, D = 25 cm (near point), f
0
= 1 cm and f
e
= 2 cm
∴m=
1
20
×
2
25
= 250
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It has given that, final image formed at 25 cm from eyepiece lens, length of tube is 20cm , magnification of microscope is 100 and focal length of objective, f₀ = 1cm
we have to find the focal length of eyepiece lens.
solution : using formula, m = L/f₀(1 + D/f)
where L is tube length, D is minimum distance of clear vision of human eyes, f is focal length of eyepiece lens.
here m = 100, L = 20 cm , f₀ = 1 cm , D = 25 cm
now , 100 = 20/(1) [1 + 25/f]
⇒100/20 = 5 = 1 + 25/f
⇒4 = 25/f
⇒f = 6.25 cm
Therefore the focal length of eyepiece lens is 6.25 cm
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