Question

When an object is placed at 10cm infront of a concave mirror, its real image is formed at 40cm in front of mirror. What is the focal length of the mirror?​

Answer 1

Draw rhombus with one side of length 4.4cm angle of measure 60° Draw its diagonals measue the angles between the diagonals

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Answer 2

Answer:

magnification given is 4 times

it means (height of image/height of object) =(-v/u) =4

u=(-v) /4

now using the mirror formula

also here f=(-40) (focal length of concave mirror is negative)

1/f=1/v +1/u

1/(-40)=1/v + (-4)/v

1/(-40)= (-3)/v

v=3*40=120

u= (-120/4)=(-30)

u= (-30)cm

hence object should be 30 cm away from the pole