All protons in an atom remain packed in a small nucleius inspite of the electrostatic repulsive force among them.Why?

A small magnet of magnetic moment M is placed at broad side on position of a magnet of magnetic M', length 2l' in such a way that the axis of former coincides with the perpendicular bisector of the latter. The separation between their centres is d. Calculate the nature of interaction (force or couple ) among them. What is its limiting value, when d becomes very large ?

Two insulated charged copper spheres A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is 6.5 xx 10^-7 C ? The radii of A and B are negligible compared to the distance of separation. What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved?

A magnetic field set up using Helmholtz coils is uniform in a small region and has a magnitude of 0.75 T. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particles all accelerated through 15 kV enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is 9.0 xx 10^5 V m^-1 make a simple guess as to what the beam contains. Why is the answer not unique?

Calculate the magnitude of the electrostatic force exerted by the proton on the electron in the hydrogen atom and compare it with the weight of the electron. Given that mass of electron is 9.1 xx 10^-31 kg, charge on electron is 1.6 xx 10^-19 C and radius of hydrogen atom is 0.53 overset(@)A .

Calculate the distance between two protons such that electrical repulsive force between them is equal to the weight of either.

The dimensions of an atom are of the order of an angstrom. Thus there must be large electric fields between the protons and electrons. Why, then is the electrostatic field inside a conductor zero?

Suppose we have a large number of identical particles, very small in size. Any two of them at 10 cm separation repel with a force of 3 x 10^-10N. Suppose you measure the repulsion and find it 6xx10^-6N . How many particles were there in the group?

Molecules in air in the atmoshpere are attracted by gravitational force of the earth. Explain why all of them do not fall into the earth just like an apple falling from a tree.