Find the focal length of given concave mirror by using two pin method
Answers
To determine the focal length of a concave mirror, by obtaining image of a distant object.
Theory -concave mirror, like a plane mirror, obeys the laws of reflection of light.1.Rays of light from object - The rays of light coming from a distant object e.g. sun or a distant building can be considered to be parallel to each other. 2.When these parallel rays of light fall on a concave mirror along its axis, reflect and meet at a point in front of the mirror, which is called as Principal focus of the mirror.
3.A real, inverted and very small image size is formed at the focus of the mirror.
4.Focal Length - The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.
Answer:
It is possible to establish the approximate focal length of the given concave mirror by obtaining an image of a distant tree on the wall. This method is known as two pin method.
Explanation:
AIM: To use the two-pin method to determine the concave mirror's focal length.
APPARATUS REQUIRED: Concave mirror optical bench, object and image pins, and meter rule are the apparatus.
PROCEDURE:
1) By getting the image of a far-off tree on the wall, the approximate focal length of the given concave mirror is determined.
2) Next, the concave mirror is put on a stand with one pin fixed to another stand before being put on the optical bench.
3) In front of the mirror, the item needle is kept. Between the mirror and the object needle, a second needle is inserted. Until there is no longer a parallax error between the images of O and I, needle I is moved.
MO (u) and MI (v) are measurements of distance. The detected object and image distance are provided.
4) The object's position is altered, moving it gradually closer to the mirror while taking care to ensure that a true image is obtained. This occurs when an object is farther away from the mirror than its focal length.
To determine the values of MO and MI in each example, this is done again (six observations).
5) V vs. U graph is plotted. It's going to curve. A line OP is drawn with a 45° angle. At point P, both axes ought to intersect the curve.
The result is calculated using this graph and the focal length calculation formula.
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