Question

An angular magnification (magnifying power) of 30 X is desired using an objective of focal length 1.25 cm and an eyepiece of focal length 5cm. How will you set up the compound microscope ?

Answer 1

In normal ajustment, image is formed at least distance of distinet vision, d = 25 cm Angular Magnification of eye piece `=(1+(d)/(f_(e)))=(1+(25)/(5))=6` As total Magnification is 30, Magnification of objective lens.
`m=(30)/(6)=5`
`m=(upsilon_(0))/(-u_(0))=5, or v_(0)=-5u_(0)`
As `(1)/(v_(0))-(1)/(u_(0))=(1)/(f_(0))`
`(1)/(-5u_(0))-(1)/(u_(0))=(1)/(1.25)`
`(6)/(-5u_(0))=(1)/(1.25)`
`u_(0)==(-6xx1.25)/(5)=-1.5cm.`
i.e. object should be held at 1.5 cm in - front of objective lens
As `v_(0)=-5u_(0)`
`v_(0)=-5(-1.5)=7.5cm`
From `(1)/(upsilon_(e))-(1)/(uu_(2))=(1)/(f_(e))`
`(1)/(u_(e))=(1)/(v_(e))-(1)/(f_(e))`
`=-(1)/(25)-(1)/(5)=-6//25`
`u_(e)=(-25)/(6)=-4.17cm`
`therefore` Seperation between the objective lens and eye piece
`|u_(e)|+|v_(0)|`
`=4.17+7.5`
`=11.67cm`