CBSE Class 12 Physics 2017 Delhi Set 1 Paper

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Question : 9
Total: 26
Define the magnifying power of a compound microscope when the final image is formed at infinity. Why must both the objective and the eyepiece of a compound microscope have short focal lengths? Explain.
Solution:  

Definition of magnifying power
Reason for short focal lengths of objective and eyepiece
Magnifying power is defined as the angle subtended at the eye by the image to the angle subtended (at the unaided eye) by the object.
(Alternatively: Also accept this definition in the form of formula.)
m=m0×me=
L
f0
×
D
fe

To increase the magnifying power both the objective and eyepiece must have short focal lengths (. as m=
L
f0
×
D
fe
)
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