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An angular magnification of 30 X is desi...

An angular magnification of 30 X is desired using an object lens of focal length 1.25 cm and an eyepiece of focal length 5 cm. How will you set up the compound microscope?

Text Solution

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Angular magnification of the eye piece `=1+(D)/(f_(e))`
i.e., `m_(e)=1+(25)/(5)=6` where D = 25 cm (least distance of vision)
We know that `m=m_(0)m_(e)`
i.e., `m_(0)=(m)/(m_(e))=(30)/(6)=5`
Hence, `because (v)/(u)=m, v=5u`
using `(1)/(v)+(1)/(u)=(1)/(f_(0))`
we get `(1)/(5u)+(1)/(u)=(1)/(1.25)`
`(+6)/(5u)=(4)/(5)`
`because u=1.5cm`. For a real object at u = -1.5 m
v = |5u| = 7.5 cm
The object should be placed 1.5 cm from the object lens.
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Knowledge Check

  • An astronomical refractive telescope has an objective of focal length 20 m and en eyepiece of focal length 2 cm.

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