ELECTRIC CHARGES AND FIELDS PART 1

ELECTRIC CHARGES AND FIELDS PART 1

1      ELECTROSTATIC:  Is the study of charge at rest.

        It is also called Frictional electricity or Static electricity.

        Some applications of electrostatics are

(i)      Different types of appliances work on the principle of electrostatics e.g., microphones, cathode ray tubes, components like capacitors in radio, television computer, radars etc. Sensitive instruments are protected from external electric fields with the help of electrostatic shielding.

(ii)    Natural phenomena like Lightning and thunders can be explained by using the knowledge of electrostatics.

(iii)   Energy conservation is done with the help of power factor correctors which work on the principle of electrostatics       

(iv)    Spraying of paints and powdered coatings are done with the help of principle of electrostatics.       

(v)     Pollution is being checked by methods of electrostatics by electrostatic precipitation of fly ash.

2     ELECTRIC CHARGE: Electric charge is an intrinsic characteristic of the fundamental particles due to which these experiences a force of attraction or repulsion. Since the study of electric charge at rest is called static electricity, we also can say charge is the amount of the electricity carried out by a substance.

SI unit of charge is coulomb (C).

CGS unit of charge is stat coulomb,  1C = 3 x 10⁹ stat coulomb

2.1 TWO KINDS OF CHARGES: When two bodies are rubbed against each other then due to friction charge is produced. When we rub two bodies, one body gains electrons while other body loses. The bodies which gain the electrons acquire –ve charge and the body which losses the electrons acquire +ve charge. Unlike charges attract each other and the like charges repel each other.

3   BASIC PROPERTIES OF ELECTRIC CHARGE

3.1 Additivity of charges

Charges add up like real numbers. If a system contains n charges q₁, q₂, q₃,………… q_n. Then the total charge of the system is q₁ + q₂ + q₃ + ……..…+ q_n.

3.2 Conservation of charge: Net charge can neither be created nor be destroyed in an isolated system.

Examples Showing the conservation of charge

(i)  In pair production also, the charge is conserved. In this case, γ-ray photon on interacting with matter transforms into an electron (e^-) and positron (e+).

                                              γ     →   e^-    +   e⁺     (pair production)

(ii) In annihilation of matter, an electron (e^-) combines with a positron (e+) to produce two γ   ray photons.

                                             e^-    +   e⁺      →     γ  +  γ

3.3 Quantization of charge: According to the quantization, charge on a body is always integral multiple of the smallest basic unit of the charge i.e. of ‘e’

Let q = total charge on body, and e = 1.6 x 10^-19C charge on electron then

q  =  ±ne                     where n = 1,2,3,4………..

Cause of Quantization: because only integral no. of electrons transferred from a body to another body therefore charge on the other body is always the multiples of the charge on an electron.