Which of the following can make a parallel beam of light when light from a point source is incident on it?

Time taken by the laser beam to return to Earth after reflection from the Moon = 2.56 s Speed of light = 3 × 108 m/s Time taken by the laser beam to...

(d) first increases then decreases. EXPLANATION:  The parallel beam of light converges at the focus on the other side and then diverges. Hence till the person moves to the focus the intensity...

Overall luminous efficiency =Total luminous flux / Power input =35x685/100 = 239.75 lumen/W

(b) The emergent beam is white. (c) The light inside the slab is split into different colours.

The illuminance will not change.

The correct answer is (c) 2%

The correct answer is (a) 40 lux

The correct answer is (c) I∝1/r3

(a) remains constant

(b,c) If faces of prism on which light is incident & from which it emerge are parallel, then angle of prism will be zero & so deviation will also be...