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⭕ Explain it with proper sign convention..Thanks !
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Asked by jhajuhi19 | 25 Aug, 2020, 04:40: PM
answered-by-expert Expert Answer
The concave lens of focal length 20 cm when placed in contact with plane mirror. 
 
The focal length of concave lens is 20 cm 
Thus, fc = -20 cm 
Focal length of plane mirror, fp = ∞
 
Focal length of that convex mirror is, 
1 over F space equals space 1 over f subscript C plus 1 over f subscript p plus 1 over f subscript C space... space left parenthesis W h e n space t h e space l i g h t space r a y space f a l l s space o n space t h e space c o n c a v e space l e n s space i t space w i l l space t h e n space r e f r a c t space a n d space i n c i d e n t space o n space p l a n e space m i r r o r space a n d space a f t e r space r e f l e c t i n g space w i l l space a g a i n space i n c i d e n t space o n space c o n c a v e space l e n s space a n d space t h e n space w i l l space d i v e r g e space o u t space f r o m space c o n c a v e space l e n s right parenthesis space therefore 1 over F space equals space 2 over f subscript C plus 1 over f subscript p space equals space fraction numerator 2 over denominator negative 20 end fraction plus 1 over infinity space equals space fraction numerator 2 over denominator negative 20 end fraction plus 0 equals space fraction numerator 1 over denominator negative 10 end fraction therefore F space equals space minus 10 space c m space
 
As the focal length is negative the combination will act like concave mirror. 
 
Thus, 
correct option is (4) - Concave mirror of focal length 10 cm. 
Answered by Shiwani Sawant | 26 Aug, 2020, 01:49: AM
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