Electric Charges and Fields — Physics STD 12 Science — Question

Answer the following questions:
Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why?

If an electric current flows through a long copper wire, then what is the magnetic field inside the tube?

In an unbiased p-n junction, holes diffuse from the p-region to n-region because,

1. Free electrons in the n-region attract them.
2. They move across the junction by the potential difference.
3. Hole concentration in p-region is more as compared to n-region.
4. All the above.

A capacitor has capacitance C. Is this information sufficient to know what maximum charge the capacitor can contain? If yes, what is this charges? If no, what other information is needed?

If in any electric circuit, phase of current lags the phase of potential difference by 90°, then what is the nature of reactance of the circuit?

If all the particles of a system lie in X-Y plane, is it necessary that the centre of mass be in X-Y plane?

The spring used in a moving coil galvanometer is of low torsion constant. Why?

Answer the following questions:
Why is diamagnetism, in contrast, almost independent of temperature?

What will be the change in the force acting on a point charge placed on its axis if its distance is doubled?

The thermal energy developed in a current-carrying resistor is given by U = i² Rt and also by U = Vit. Should we say that U is proportional to i² or i?