Advertisements
Advertisements
Question
The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will ______.
Options
act as a convex lens only for the objects that lie on its curved side.
act as a concave lens for the objects that lie on its curved side.
act as a convex lens irrespective of the side on which the object lies.
act as a concave lens irrespective of side on which the object lies.
Solution
The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will act as a convex lens irrespective of the side on which the object lies.
Explanation:
If object lies on curved side then R1 = +20 cm and R2 = `oo`, μ1 = 1, μ2 = 1.5
`1/f = (mu_2 - mu_1) (1/R_1 - 1/R_2)`
`1/f = (1.5 - 1) (1/20 - 1/oo) = 0.5/20 = 5/200 = 1/40`
F = + 40 cm
If object lies on plane side R1 = `oo` and R2 = – 20 cm, μ1 = 1, μ2 = 1.5
`1/f = (mu_2 - mu_1) (1/R_1-1/R_2)`
`1/f = (1.5 - 1)(1/oo - (- 1/20)) = 0.5 xx (+ 1/20)`
`1/f = 5/200`
f = + 40 cm
So, lens will always act as a convex lens irrespective of the side on which objects lie.
APPEARS IN
RELATED QUESTIONS
A man uses a concave mirror for shaving. He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal length of the mirror.
The image of an extended object, placed perpendicular to the principal axis of a mirror, will be erect if
(a) the object and the image are both real
(b) the object and the image are both virtual
(c) the object is real but the image is virtual
(d) the object is virtual but the image is real.
A narrow pencil of parallel light is incident normally on a solid transparent sphere of radius r. What should be the refractive index is the pencil is to be focussed (a) at the surface of the sphere, (b) at the centre of the sphere.
A converging lens of focal length 40 cm is kept in contact with a diverging lens of focal length 30 cm. Find the focal length of the combination .
How can the spherical aberration produced by a lens be minimized?
Answer the following question.
Under what conditions is the phenomenon of total internal reflection of light observed? Obtain the relation between the critical angle of incidence and the refractive index of the medium.
Focal length of a mirror is given by ______.
You are given four sources of light each one providing a light of a single colour – red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the following statements is correct if the source of yellow light is replaced with that of other lights without changing the angle of incidence?
A car is moving with at a constant speed of 60 km h–1 on a straight road. Looking at the rear view mirror, the driver finds that the car following him is at a distance of 100 m and is approaching with a speed of 5 km h–1. In order to keep track of the car in the rear, the driver begins to glance alternatively at the rear and side mirror of his car after every 2 s till the other car overtakes. If the two cars were maintaining their speeds, which of the following statement (s) is/are correct?
A thin convex lens of focal length 25 cm is cut into two pieces 0.5 cm above the principal axis. The top part is placed at (0, 0) and an object placed at (– 50 cm, 0). Find the coordinates of the image.
