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2. Study Of Charges When they are at rest 3. Glass Rod + silk cloth- Reason- Redistribution of charges This redistribution of charges is known as Induction 4. Like Charges + + 5. Unlike charges + - 6. Charge neither be created nor be destroyed but we can transfer it from one point to anther. 7. The Force of attraction or repulsion between two charges is directly proportional to product of magnitude of two charges and inversely proportional to square of the distance between them + + 1 2 elec 2 q q F Z r 8. Where Z=1/4k 0 is permittivity of medium 0 is permittivity of Vacuum and free space Where K= 9 x 109 Nm2/C2 0 = 8.8 5 x 10-12 C2/Nm2 9. Dielectric constant (k) is defined as the ratio of the permittivity of the medium to the permittivity of vacuum. i.e. k = / 0 , = k 0 . K=1 (For free space) K>1(For any other medium) 10. 1 2 elec 2 1 2 elec 2 0 q q F Z r q q1 F 4 k r 11. a charge of one coulomb is defined as the charge which when kept in vacuum at a distance of 1 metre from an identical charge repels it with a force of 9 x 109 N. 1 2 elec 2 0 9 elec 2 q q1 F 4 k r 1 1 F 9 10 1 12. Coulombs law is applicable for point charges only. However it is also applicable to small spherical charges, whose radii are very small as compared to the distance between the them. 13. The forces obtained by Coulombs law are vector quantities. As shown in fig 1, the force acting on charge q1 due to q2 is F12 and the force acting on q2 due to q1 is F21 14. 1 2 1221 2 0 12 1 2 2 1 1 2 2112 2 0 12 2 1 12 21 21 ^ ^ ^ q q1 F . . r 4 k r W here r is unit vector directed from q to q . Similarly the force exerted by ch arg e q on ch arg e q is q q1 F . . r 4 k r W here r is unit vector directed from q to q As r r then F 12F i.e. the forces are oppositely directed and have equal magnitude. 15. the resultant force acting on a given charge is given by the vector sum of the individual forces exerted on the given charge by all other charges. F0 = F01 + F02 + F03 16. 0 1 01 103 0 10 0 2 02 203 0 20 0 3 03 303 0 30 0 31 2 0 10 20 303 3 3 0 10 20 30 q q1 F r 4 r q q1 F r 4 r q q1 F r 4 r q qq q F r r r 4 r r r 17. When a body is charged, the charge is distributed equally over the body. The distribution of charge may be one. two or three dimensional. Depending upon that it can have charge. 18. 1. Linear charge density :- When a charge is distributed along a line (straight or curved), the charge distribution is called linear charge distribution and the charge per unit length is called linear charge density. q L 19. 2. Surface charge density :- When a charge is distributed over a surface (plane or curved), the charge distribution is called surface charge distribution and the charge per unit area is called surface charge density. Q A 20. 3. Volume charge density :- When a charge is distributed over the entire volume of the body, the charge distribution is called volume charge distribution & charge per unit volume is called volume charge density. q V 21. In order to explain how two charges attract or repel each other even though there is no physical contact between them, the concept of electric field is introduced. According to this concept, An electric charge produces an electric field in the surrounding space. When another charge is brought in this space, the field exerts a force on that charges. This is the force which we have studied by Coulombs Law. 22. The strength of the electric field is expressed in terms of a quantity called electric intensity. The electric intensity at any point in an electric field is defined as the force acting on a unit +ve charge placed at that point. F E on which force acts q 23. 1 0 2 0 1 0 2 0 0 1 2 0 q q1 F 4 r q q1 4 r E q q1 E 4 r Unit of E is N/C. Electric intensity is a vector quantity directed away from + ve due to which charge always and towards - ve charge always. 24. The ratio of permittivity of a medium to the permittivity of vacuum or air (free space) is called the dielectric constant of that medium (k) = K 0 where k is dielectric constant 0 K 25. Electric Potential at a point in an electric field is defined as the work which must be done in bringing the unit +ve test charge from infinity to a point in the electric field, against the direction of electric intensity. W V q 26. Ask Your Doubts For inquiry and registration, call 9011041155 / 9011031155.