Derivation of formula for curved mirrors
Answers
Answer:
Suppose an object is placed u cm in front of a spherical mirror of focal length f such that the image is formed v cm from the mirror, then u, v and f are related by the equation;
1/f= 1/u + 1/v.
This equation is referred to as the mirror formula. The formula holds for both concave and convex mirrors.
When applying the mirror formula, it is necessary to observe the following points:
That all distances are measured from the mirror as the origin.
All real distances are positive while all virtual distances are negative.
A concave mirror has a positive focal length while a convex mirror has a negative focal length.
Example
Determine the position, size and nature of the image of an object 4cm tall placed on the principal axis of a concave mirror of focal length 15cm at a distance 30cm from the mirror.
solution
u=30cm, f= 15cm, ho=4cm
1/v=1/f-1/u
= 1/15 – 1/30 =1/30
v =30cm
Also, m=v/u =hi/ho
Thus, hi=(30cm x 4cm)/30cm =4cm.
Thus the image formed is real and same size as the object.
Explanation:
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