Question

An object, a convex lens of focal length 20 cm and a plane mirror are arranged as shown in fig. How far behind the mirror is the final image formed? 

                                                         

Solution

Correct option is

40 cm

 

Putting u = –12 cm and f = +20 cm in the lens formula gives

v = –30 cm, i.e., the image is formed at a distance of 30 cm from the lens on the same side as the object. The distance of this image from the mirror = 30 + 10 = 40 cm. Therefore, the final image is formed behind the mirror at a distance of 40 cm from it.

SIMILAR QUESTIONS

Q1

A rectangular block of glass of refractive index μ and thickness d is placed over an ink dot made on a pice of paper lying on a table. When viewed from above, the dot will appear to be raised by an amount given by

Q2

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Q3

A convex glass lens (μg = 1.5) has a focal length of 8 cm when placed in air. What is the focal length of the lens when it is immersed in water (μw = 4/3)?

Q4

A plano-concave lens is made of glass of refractive index 1.5 and the radius of curvature of the curved face is 50 cm. The power of the lens is

Q5

A convex lens of focal length 50 cm and a concave lens of focal length 100 cm are separated by a distance of 10 cm. What is the power of the combination?    

Q6

How will the image formed by a convex lens be affected if the central portion of the lens is wrapped in black paper, as shown in fig.

                                                                            

Q7

The equi-convex lens, shown in the figure, has a focal length f. What will be the focal length of each half if the lens it cut along AB? (See fig.)

                                                                   

Q8

A person can see clearly only up to a distance of 30 cm. He wants to read a book placed at a distance of 50 cm from his eyes. What is the power of the lens he requires for his spectacles?   

Q9

A person with defective eyesight is unable to see objects clearly nearer than 1.5 m. He wants to read a book placed at a distance of 30 cm from his eyes. Find the power of the lens he requires for his spectacles.   

Q10

A small plane mirror is rotating at a constant frequency of n rotations per second. With what linear velocity (in ms–1) will a light spot move along a spherical screen of radius of curvature of R metres if the mirror is at the centre of curvature of the screen?