While a moving picture is being screened, a boy introduced a glass slab of thickness 3 cm and refractive index 1.5 between the projector and the screen. In order to have a clear picture on the screen the screen should be moved through a distance of

The time taken by a ray of light to travel through a glass slab of thickness 2 cm and refractive index 1.5 will be

In a movie hall, the distance between the projector and the screen is increased by 1% illumination on the screen is

In a movie hall the distance between the projector and the screen is increased by 1%, illumination on the screen is

An object 240 cm in front of a lens forms a sharp image on a screen 12 cm behind the lens. A glass slab 1 cm thick, having refractive index 1.50 is placed between the lens and the screen with its refracting faces perpendicular to the principal axis of the lens. (a) By how much distance the object must be moved so as to again cast a sharp image on the screen? (b) Another identical glass slab is interposed between the object and the lens. How much further the object shall be moved so as to form a sharp image on the screen.

A screen is placed at a distance of 5 cm from a point source. A 5 mm thick piece of glass of refractive index 1.5 is placed between them. What is the length of optical path between the source and the screen ?

A convex lens focuses an object 40cm from it on a screen placed 10cm away from it. A glass plate ( mu=1.5 ) and of thickness 3cm is inserted between the lens and the screen. Where should the object be placed so that its image is again focused on the screen ?

An illuminated slide is held 68cm from a screen. How far from the slide must a lens of focal length 11cm be placed (between the slide and the screen) to form an image of the slide's picture on the screen ?