WAVE OPTICS — Physics STD 12 Science — Question

Is current density a scalar or a vector quantity?

Is it possible to boil water at room temperature, say 30°C? If we touch a flask containing water boiling at this temperature, will it be hot?

A hollow metal sphere and a solid metal sphere of equal radii are given equal charges. Which of the two will have higher potential?

Name any two semiconductor alloys.

An experimenter measures the length of a rod. In the cases listed, all motions are with respect to the lab and parallel to the length of the rod. In which of the cases the measured length will be minimum?

1. The rod and the experimenter move with the same speed v in the same direction.
2. The rod and the experimenter move with the same speed v in opposite directions.
3. The rod moves at speed v but the experimenter stays at rest.
4. The rod stays at rest but the experimenter moves with the speed v.

Two proton beams going in the same direction repel each other whereas two wires carrying currents in the same direction attract each other. Explain.

Which waves are possible to be polarized in X-rays, sound waves and radio waves?

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?