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an object is placed at a distance of f/2 from a concavex lens. The image will be? A-at 3f/2,real and Inverted.B-at 2f virtual and erect. C-at f real and inverted. D-at one of the foci virtual and double size. 

Asked by Priyanka 13th November 2017, 9:35 PM
Answered by Expert
Answer:
Question: If an object is placed at a distance of f/2 from a concavex lens. The image will be? (CPMT - 1997)
 
Solution:
 
begin mathsize 12px style We space know space that comma
1 over straight v minus 1 over straight u equals 1 over straight f
It space is space given space that space straight u equals negative straight f over 2 space... left parenthesis 1 right parenthesis
Therefore comma space
1 over straight v minus fraction numerator 1 over denominator begin display style negative straight f over 2 end style end fraction equals fraction numerator begin display style 1 end style over denominator begin display style straight f end style end fraction
fraction numerator begin display style 1 end style over denominator begin display style straight v end style end fraction equals fraction numerator begin display style 1 end style over denominator begin display style straight f end style end fraction minus 2 over straight f
fraction numerator begin display style 1 end style over denominator begin display style straight v end style end fraction equals negative fraction numerator begin display style 1 end style over denominator begin display style straight f end style end fraction
straight v equals negative straight f space space space... left parenthesis 2 right parenthesis
Magnification space left parenthesis straight m right parenthesis equals straight v over straight u equals fraction numerator negative straight f over denominator begin display style fraction numerator negative straight f over denominator 2 end fraction end style end fraction equals 2
end style
Therefore, the image is virtual and double the size.
So the right option is
(D) at one of the foci virtual and double size. 
Answered by Expert 15th December 2017, 12:11 PM
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