Question

A converging lens forms a real and inverted image of an object at a distance of 100cm from it. where should an object be placed in front of the lens,so that the size of the image is twice the size of the object?​

Answer 1

Answer:

33.33 cm

Explanation:

The lens is converging . Hence, it is  convex lens.

It forms a real image at a distance of 100cm. Hence,

v = +100cm

Now, the magnification is 2 and for a lens it is

m = - v/u

Therefore, u = -v/m = -100/2 = -50cm

Hence, the object should be placed at a distance of 50cm in front of lens.

According to lens formula,

1/f=1/v=-1/u

1/f = 1/100 - 1/-50 / 1/100 + 1/50 = 3/100

f= 100/3 = 33.33 cm

Answer 2

given : v=100cm

m=-2 (since image is inverted)

v=? p=?

Explanation:

m=v/u

-2=100/u

u=-50

we need do find f for power

1/f = 1/v - 1/u

1/f = 1/p

therefore 1/p = 1/v - 1/ u

since f is in cm we need to convert it to meter so ×100

= 1/100 + 1/50 ×100

=3/100 × 100

p=3D