How can we measure the focal length of a concave mirror?

Asked by  | 11th Sep, 2008, 08:23: PM

Expert Answer:

There are two methods

1.)Lay a concave  mirror horizontally on the table. The reflected light from light rays parallel to the principle axis will converge on a common point, called the focus. Using the optics lamp, trace out at least three reflected rays (from incident parallel rays) to determine the focus. Measure the focal length for both the concave mirror and the convex mirror.

2.)Place a pin object (angled into cardboard so that the colored tip points clearly to the right) in front of a concave mirror. View the image when the object distance is 5 cm from the center of the mirror segment. Be sure to view the image at a far distance (at least the width of the table). Record information about the image: erect or inverted, magnified or demagnified. Repeat for a pin object placed at 10 cm and increments of 1 cm from 10 cm until the object distance is 20 cm. Estimate the focal length, noting that the image should become inverted when the object is placed beyond the focal length.

Answered by  | 12th Sep, 2008, 07:59: AM

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