When an object is placed 15 cm from "
a concave mirror, a real image magnified
3 times is formed - Find
a) the focal length of the mirror
b) where the object must be placed to
give a virtual image 3 times the height
of the object

Here's link to the

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Focal length(f)= -15 cm, magnification= -3 (image is real). So, -v/u=-3 ; or v=3u {v=image distance and u=object distance}. Using mirror formula,

1/f= 1/v + 1/u

-1/15 = 1/3u + 1/u

4/3u = -1/15

u= -20 cm

v =3u= 3×(-20)= -60 cm

So object is 20 cm and image is 60 cm in front of the mirror.

Explanation:

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.