Positively charged protons and neutral neutrons are packed inside the atomic nucleus. But protons, though similarly charged, do not repel each other. How do you account for this phenomenon?

Can two similarly charged balls be attracted by each other? If yes, explain how.

How do histones acquire positive charge?

An object is held between two plane parallel mirrors inclined at 45^@ to each other. How many images do you expect to see?

The classical concept of atomic structure is that negative charges are uniformly distributed inside a sphere of radius R keeping the nucleus of positive charge Ze at the centre of that sphere. An atom as a whole is electrically neutral. find out the electric field at a distance r from the nucleus, according do this atomic model.

State whether True or False : The positive charged particle of atom is proton.

It is now believed that protons and neutrons ( which constitute nucleI of ordinary matter ) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called 'up' quark ( denoted by 'u') and 'down' quark ( denoted by 'd') of charge (2)/(3) e and (-1)/(3) e respectively , together with electrons build up ordinary matter. Suggest a possible quark composition of a proton and a neutron.

Screening effect is the effect produced by intervening electrons between nucleus and valence electrons . They shield the nucleus from valence electron and effective nuclear charge decreases if there is less shielding effect the effective nuclear charge decreases Valence electrons are attracted by nucleus and repelled by other electrons. Net effective force on electrons under consideration = Z-sigma = (Nuclear charge -screening effect ) slaters formula for screening constant. If one electron is present in outermost orbit there will be no screening in that orbital. Each electrons contributes 0.35 (total electrons minus 1) present in outermost shell. In penultimate energy level electrons contribute 0.85. A contribution of 1 is from remaining electrons (present in last but one energy level) The effective nuclear charge for 4s electrons of Zn will be