Electromagnetic Waves — Physics STD 12 Science — Question

What are permanent magnets? Give one example.

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

The dielectric constant decreases if the temperature is increased. Explain this in terms of polarization of the material.

Answer the following:
What are the forms of energy into which the electrical energy of the atmosphere is dissipated during a lightning? (Hint: The earth has an electric field of about 100Vm^–1 at its surface in the downward direction, corresponding to a surface charge density = –10^–9 Cm^–2. Due to the slight conductivity of the atmosphere up to about 50km (beyond which it is good conductor), about + 1800C is pumped every second into the earth as a whole. The earth, however, does not get discharged since thunderstorms and lightning occurring continually all over the globe pump an equal amount of negative charge on the earth.)

When Wheatstone bridge is said to be balanced?

Select one donor impurity from the following : Boron (B), Aluminum (Al) and Arsenic (As).

A charged particle is projected at a very high speed perpendicular to a uniform magnetic field. The particle will:

1. Move along a circle.
2. Move along a curve with increasing radius of curvature.
3. Move along a curve with decreasing radius of curvature.
4. Move along a straight line.

Comment on the following statement: the temperature of all the molecules in a sample of a gas is the same.

An experimenter measures the length of a rod. Initially the experimenter and the rod are at rest with respect to the lab. Consider the following statements:

1. If the rod starts moving parallel to its length but the observer stays at rest, the measured length will be reduced.
2. If the rod stays at rest but the observer starts moving parallel to the measured length of the rod, the length will be reduced.

1. Is true but B is false.
2. B is true but A is false.
3. Both A and B are true.
4. Both A and B are false.