A planet is observed by an astronomical refracting telescope having an objective of focal length 16 m and an eye piece of focal length 2 cm ?

1 ) A planet is observed by an astronomical refracting telescope having an objective of focal length 16 m and an eye piece of focal length 2 cm ?

Solution : -

Distance between objective and eye piece lens : -

L  =  F˳ + Fe  =  16 + 0.02  =  16.02 m .

Angular magnification  =  F( objective )  /  F( eye piece )  ,

Angular magnification  =  F˳ / Fe  =  16  / 0.02  =  - 16 / 0.02 ,

F˳ is  ( - ve )  and  Fe is  ( + ve )  in astronomical telescope .

So , the image formed by telescope is inverted .

 

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2 ) If a lens is cut into two pieces perpendicular to the principal axis and only one part is used , so the intensity of the image will be : -

A ) increased ,                                                    B ) decreased ,

C ) remain same ,                                              D ) None of these ,

Correct Answer : -   C ) remain same ,

Solution : -

So number of rays will remain same because number of rays depend on intensity . So , intensity will remain same .

 

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