Question

A converging lens forms a three times magnified image of an object, which can be take on a screen. If the focal length of the lens is 30 cm, then the distance of the object from the lens

Answer 1

Answer:

less than 10

Explanation:

D

must not be less than 10 cm

If image is to be formed on the screen,

v−u=40

Also

v

1

−

u

1

=

f

1

Using above equations one can write,

f

1

=

40+u

1

−

u

1

Hence u

2

+40u+40f=0

So there to exist no such u, Determinant of the equation <0

Hence, 40

2

−4(1)(40f)<0

Hence f>10cm