Electric Charge
The fundamental property of matter with which it exerts Coulomb force. Charge is of two types, positive and negative. Like charges repel and unlike charges attract. A charged particle can even attract an uncharged particle. Charges can be detected using gold leaf electroscope (GLE). The unit of charge is coulomb (C) e/m is called specific charge.
Charge is conserved:- (a) in an isolated system charge can neither be created nor be destroyed (b) total charge of the universe is constant (c) charge can be created or destroyed but in equal and opposite pairs, for example , a Υ ray of energy ≥ 1.02 MeV can be converted to electron and positron that is,
Eλ (≥ 1.02 MeV) ---> eelectron + epositron
This process is called pair production. Even electron and position combine to form γ ray (charge destruction)
e + e+ ---> γ(Eγ = 1.2 MeV).
This processes called pair annihilation.
Charge is quantized:- A charged body will have charge Q = ±ne where n = 1, 2, 3... and e is charge on an electron. A body is charged by the transfer of electrons. If it gains electrons it is negatively charged. If it loses electrons it is positively charged. Though there are particles called quarks which may have chargee/3 or 2e/3 since these are generated during disintegration of nucleus (neutron, proton and so on). Therefore, these cannot be transferred. Charge on an electron = 1.6 x 10-19 coulomb (c).
1 esu = 1/3 × 109 C (1 emu = 10 coulomb)
A body can be charged (a) by rubbing, for example glass rod with silk cloth (b) by induction (c) by physical contact of uncharged body with a charged body. (d) A capacitor can be charged with a battery.
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