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 $u$) of charge $+(2 / 3) e,$ and the 'down' quark (denoted by $d$) of charge $(-1 / 3) e$ together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

A body can be negatively charged by

By which instrument, the charge on object can be detected ?

What type of charges are obtained on silk cloth and glass rod ?

One metallic sphere $A$ is given positive charge whereas another identical metallic sphere $B$ of exactly same mass as of $A$ is given equal amount of negative charge. Then