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Question
An object is placed at 60 m in front of a concave mirror. If its radius of curvature is 40 m, then find the image distance.
An object is placed at 60 m in front of a concave mirror. If its radius of curvature is 40 m, then find the image distance.
20 
30 
60 
120 
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Solution
The correct option is B 30
Given:
Radius of curvature, R=−40 m
Object distance, u=−60 m
Let the sign convention be such that the object distance is negative i.e. positive direction is taken along the direction of the incident ray.
From mirror formula,
1v+1u=1f
where:
v: Position of image
f: Focal length
But focal length is half of the radius.
⟹f=R2=−20 m
⟹1v+1−60=1−20
v=−30 m
Negative sign represents that object and image are on the same side of mirror.
30
Given:
Radius of curvature, R=−40 m
Object distance, u=−60 m
Let the sign convention be such that the object distance is negative i.e. positive direction is taken along the direction of the incident ray.
From mirror formula,
1v+1u=1f
where:
v: Position of image
f: Focal length
But focal length is half of the radius.
⟹f=R2=−20 m
⟹1v+1−60=1−20
v=−30 m
Negative sign represents that object and image are on the same side of mirror.
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