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Solution


Q.

If the focal length of objective lens is increased then magnifying power of              [2014]
1 microscope will increase but that of telescope decrease  
2 microscope and telescope both will increase  
3 microscope and telescope both will decrease  
4 microscope will decrease but that of telescope will increase  

Ans.

(4)

Magnifying power of a microscope,

         m=(Lfo)(Dfe)

where fo and fe are the focal lengths of the objective and eyepiece respectively, and L is the distance between their focal points and D is the least distance of distinct vision.

If fo increases, then m will decrease.

Magnifying power of a telescope, m=fofe

where fo and fe are the focal lengths of the objective and eyepiece respectively.

If fo increases, then m will increase.