A Source Of Light Lies On The Angle Bisector Of Two Plane Mirrors Inclined At An Angle θ, So That The Light Reflected From One Mirror Does Not Each Other Mirror Will Be 

A good photographic print is obtained by an exposure of two seconds at a distance of 20 cm from the lamp. The time of exposure required to get an equally good result at a distance of 40 cm is: 

A camera objective has an aperture diameter d. If the aperture is reduced to diameter d/2, the exposure time under identical conditions of light should be made:   

A film projector magnifies a 100 cm² film strip on a screen. If the linear magnification is 4, the area of the magnified film on the screen is:

The resolution limit of the eye is 1 minute. At a distance x km from the eye, two persons stand with a lateral separation of 3 metre. For the two persons to be just resolved by the naked eye, x should be:

The minimum light intensity that can be perceived by the eye is about 10^–10 watt per metre². The number of photons of wavelength  metre that must enter the pupil of area 10^–4 m² per sec for vision is approximately equal to:    

An observer looks at a tree of height 15 metres with a telescope of magnifying power 10. To him the tree appears:  

The distance between the eye lens and cross-wires in Ramsden’s eye-piece which has a field lens of focal length 1.2 cm is:

If an astronomical telescope has objective and eye-piece of focal lengths 200 cm and 4 cm respectively, then the magnifying power of the telescope for the normal vision is:    

A plane mirror which rotates 10⁴ times per minute reflects light on to a stationary mirror 50 m away. This mirror reflects the light normally so that it strikes the rotating mirror again. The image observed in the rotating mirror is shifted through 2.4 minutes from the position it occupies. When the rotating mirror is stationary, what is the speed of light? 

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that the end closer to the pole is 20 cm away from it. Find the length of the image