Question

when an object is placed 20cm from a concave mirror a real image magnified three times is formed find :
A)the focal length of the mirror
B)where must be the object be placed to give a virtual image three times the height of the object​

Answer 1

Step-by-step explanation:

GIVEN

Magnification, m= -3

Object distance, u= -20cm

USING MAGNIFICATION FORMULA

m = -v/u

-3 = - v/ -20

v = - 60 cm

distance of the image from the mirror is - 60

USING MIRROR FORMULA

1/f = 1/v +1/u

1/f = 1/ -60 + 1/ -20

f = -15 cm

the focal length of the mirror is -15

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to find the distance of the object from the mirror

USING MAGNIFICATION FORMULA

m = h (height of image) / h (height of object)

m = -v/u

as per question ''three times the height of the object''

v= -3u

USING MIRROR FORMULA

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

u= -10 cm

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hope it helped....... :)

Answer 2

Answer:

m=h2/h1

m=-v/u=3

v=-3u

applying mirror formula

1/v+1/u=1/f

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

1/u=1/-15_1/3u

u=-10cm