3
Question
A concave mirror of focal length 10 cm and convex mirror of focal length 15 cm are placed facing each other 40 cm apart. A point object is placed between the mirrors on their common axis and 15 cm from the concave mirror. One of the images is produced by the reflection first at concave mirror and then at convex mirror. The distance of this image from convex mirror is
A concave mirror of focal length 10 cm and convex mirror of focal length 15 cm are placed facing each other 40 cm apart. A point object is placed between the mirrors on their common axis and 15 cm from the concave mirror. One of the images is produced by the reflection first at concave mirror and then at convex mirror. The distance of this image from convex mirror is
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Solution
The correct option is A 6 cm
Using mirror formula for first reflection by the concave mirror,
v=ufu−f=(−15)(−10)−15+10
=150−5=−30 cm
This image will behave as the object for the convex mirror
For the reflection at the convex mirror,
u=−10 cm and f=15 cm
(considering the direction in which rays are travelling to be positive)
v=ufu−f=(−10)(15)−10−15=6 cm
Using mirror formula for first reflection by the concave mirror,
v=ufu−f=(−15)(−10)−15+10
=150−5=−30 cm
This image will behave as the object for the convex mirror
For the reflection at the convex mirror,
u=−10 cm and f=15 cm
(considering the direction in which rays are travelling to be positive)
v=ufu−f=(−10)(15)−10−15=6 cm
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