Consider the two mirrors shown below: the one on the left is concave while the o

Question

Consider the two mirrors shown below: the one on the left is concave while the one on the right is convex. Both also show the paths of light rays which enter parallel to the optical axis from infinity. What are the signs of the focal lengths of the two mirrors?

Select one:

a. Both mirrors have a positive focal length

b. The left mirror has a positive focal length, the right mirror has a negative focal length

c. The left mirror has a negative focal length, the right mirror has a positive focal length

d. Both mirrors have a negative focal length

Explanation / Answer

Solution:

Option C should be right.

The left mirro should have negative focal length , and the right mirror should have positive focal length.

explanation: Just take direction of light as positive and all the directions are measured from pole now if we go measuring the distance from pole to F it will be opposite to direction of light comming from object. hence focal length should be negative in left diagram.

same goes for right diagram.

thanks.

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