A point object is placed at a distance of 25 cm from a convex lens of focal length 20 cm. If a glass slab of thickness, t and refractive index, 1.5 is inserted between the lens and the object, the image is formed at infinity. The thickness, t is

Question

A point object is placed at a distance of 25 cm from a convex lens of focal length 20 cm. If a glass slab of thickness, t and refractive index, 1.5 is inserted between the lens and the object, the image is formed at infinity. The thickness, t is (A) 15 cm (B) 5 cm (C) 10 cm (D) 20 cm

Tardigrade Admin · Accepted Answer

In the situation given, the image will be formed at infinity, if the object is at focus of the lens
i.e., at

20 c m

from the lens.
Hence, shift in position of object

x = 25 - 20 = (1 - \frac{1}{μ}) t

5 = (1 - \frac{1}{1.5}) t

t = 15 c m

Q. A point object is placed at a distance of 25cm from a convex lens of focal length 20cm. If a glass slab of thickness, t and refractive index, 1.5 is inserted between the lens and the object, the image is formed at infinity. The thickness, t is

15 cm

5 cm

10 cm

20 cm

In the situation given, the image will be formed at infinity, if the object is at focus of the lens i.e., at 20cm from the lens. Hence, shift in position of object x=25−20=(1−μ1​)t 5=(1−1.51​)t t=15cm

Q. A point object is placed at a distance of $25 c m$ from a convex lens of focal length $20 c m$ . If a glass slab of thickness, $t$ and refractive index, $1.5$ is inserted between the lens and the object, the image is formed at infinity. The thickness, $t$ is

In the situation given, the image will be formed at infinity, if the object is at focus of the lens
i.e., at $20 c m$ from the lens.
Hence, shift in position of object
$x = 25 - 20 = (1 - \frac{1}{μ}) t$
$5 = (1 - \frac{1}{1.5}) t$
$t = 15 c m$