Question

) A double convex lens has 10cm and 15cm as its two radii of curvature. The image of an object placed 30cm from the lens, is formed at 20cm from the lens on the other side. Find the refractive index of the material of the lens. What will be the focal length ?​

Answer 1

Answer:

Lens maker formula is as follows

f

1

=(n−1)(

R

1

1

−

R

2

1

)

Put R

1

=20cm R

2

=−20cm, and n=1.5 we will get f=20cm

Thin Lens Formula is as follows

f

1

=

v

1

−

u

1

v = image distance , u = object distance = −10cm and f=20cm we get v=−20cm

Nature of the image

The image is on the same side as the object because u and v both are negative. As the lens is convex so for being on the same side the image will be virtual and thus erect.

Size =magnification×object size= ∣

u

−v

∣×2cm = 4cm