Design an activity using concave mirror to prove that it is converging in nature. Also deduce a method to find its rough focal length.
Answers
"Take a concave mirror with its reflecting surface held facing the sun. Hold a paper close to the mirror and direct the reflected light onto it. Make sure that the sharpest point of light is visible on the paper.
After holding for a few minutes, you will see smoke coming out of the paper, and eventually it will catch a fire. The fire took place because of the concentrated sunlight directed at the paper.
This activity shows that concave mirror is convergent in nature. Its focal length can be deduced by obtaining the image of an object kept at a distance.
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Answer:
The following activity can be used to determine the principal focus and approximate focal length of a concave mirror.
(1) Place the mirror vertically on a table.
(2) Place an object (a pencil) in front of the mirror and move it towards and away from the mirror.
(3) Find the approximate spot where the reflection of the object changes from upright to upside down. This point is the focus of the mirror. Measure the distance between this point and the mirror. This length is the focal length of the mirror.