An object is placed at a distance of 20 cm from a convex lens of radius of curvature of 20 cm. Find the nature, position and size of the image.
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Answers
f=10
1/v=1/f+1/u
1/v=1/20
v=20 cm
The image is real and inverted as v is positive and it will form at 20 cm of other side of optical centre or we can say it will form on 2F2.
m=v/u
m=20/-20
m=-1
As m is negative the image formed will be enlarged.
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Ray Optics and Optical Instruments
Problems on Mirror and Magnification Formula
An object is placed at a di...
PHYSICS
An object is placed at a distance of 20 cm from a convex mirror or radius of curvature 40 cm. At what distance from the object should a plane mirror be placed so that the images due to the mirror and the plane mirror are in the same plane?
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ANSWER
Given: An object is placed at a distance of 20 cm from a convex mirror or radius of curvature 40 cm.
To find the distance at which the plane mirror should be placed such that the images due to the mirror and the plane mirror are in the same plane
Solution:
According to the given criteria,
Object distance from convex mirror, u=−20cm
Radius of curvature of convex mirror, R=40cm
Focal length of the convex mirror, f=
2
R
=
2
40
=20cm
Now applying the mirror formula we get,
f
1
=
v
1
+
u
1
⟹
20
1
=
v
1
+
−20
1
⟹
v
1
=
20
1
+
20
1
⟹v=10cm
So the distance is formed on the opposite side of the object at a distance of 10 cm from the mirror as shown in above fig.
The distance between object and image is u+v=20+10=30cm
When plane mirror is placed in front of object and in order to get image at same position as convex mirror, the mirror should be place at
2
30
=15cm, as in plane mirror the object distance from mirror is equal to image distance from the plane mirror (refer above fig).
Hence the distance at which the plane mirror should be placed such that the images due to the mirror and the plane mirror are in the same plane = 15cm