Electromagnetic Waves — Physics STD 12 Science — Question

Light from a point source falls on a screen. If the separation between the source and the screen is increased by 1%, the illuminance will decrease (nearly) by:

1. 0.5%
2. 1%
3. 2%
4. 4%

Why is it easier to swim in sea water than in fresh water?

What are the main sources of electro- magnetic waves?

Write mirror and its types.

Choose the correct alternative:
Alloys of metals usually have (greater/ less) resistivity than that of their constituent metals.

An NCC parade is going at a uniform speed of 6km/h through a place under a berry tree on which a bird is sitting at a height of 12.1m. At a particular instant the bird drops a berry. Which cadet (give the distance from the tree at the instant) will receive the berry on his uniform?

Answer the following question:
When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

Define electric dipole moment. Write its S.I. unit.

The polarising angle of a medium is 60°. What is the refractive index of the medium?