A student has three concave mirrors A, B and C of focal lengths 20cm, 15cm and 10cm respectively. For each concave mirror, he performs the experiment of image formation for three values of an object distance of 30cm, 10cm and 20cm. Give reason and answer the following:

1. For the three object distances identify the mirror which will form an image equal in size to that of the object. Find at least one value of object distance.
2. Out of the three mirrors identify the mirror which would be used for shaving purpose.

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Solution

Focal length of mirror
A = 20cm
B = 15cm
C = 10cm
Object distances for these mirrors are 30cm, 10cm and 20cms respectively.
1) Mirror C will produce an image of the same size as an object because the object is placed on C.
2) Mirror B can be used as shaving mirror because when the object is kept between P and F we get virtual, erect and magnified image.

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