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Question:  A point object is kept between a plane mirror and a concave mirror facing each other.The

distance between the mirrors is 22.5cm.Plane mirror is placed perpendicular to the

principal axis of the concave mirror.The radius of curvature of the concave mirror is

20cm.hat should be the distance of the object from the concave mirror so that after two

successive reflections the final image is formed on the object itself.

Answer:

!

! ! !

 " "!0v x + =

!

!0

!0 "

 x v 

 x 

=

#irst image will form at $!

This!

v 

will come in negative so adding the negative sign makes the image distance refer

onl% to magnitude

!0 " 22.5 22.5 "

!0 "

 x  x 

 x 

= +

!0  x  & ' x  " (5) '!0 "  x )

0 & " (50 "  x 2 * (5  x 

 x 2 " (5u * (50 & 0

Solving 

2(5 (5 " ( (50

2 x 

± ×=

(5 !5

2 x 

±=

 & +0 cm and !5 cm

,orrect answer is !5 cm as +0 cm is be%ond plane mirror.

8/17/2019 Ansd

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