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?   


Correct option is


If a mirror rotates through an angle θ, the image rotates through an angle 2θ. Therefore, the linear speed of the light spot is




Two transparent media A and B are separated by a plane boundary. The speed of light in medium A is  and in medium B  The critical angle for which a ray of light going from A toB is totally internally reflected is   


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)?


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


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?    


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.



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.)



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?   


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.   


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? 



A ray of light incident normally on face AB of an isosceles prism travels as shown in fig. The least value of the refractive index the prism must have should be