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Electrostatics ppt use for 12th science 2.pptx
- 1. CHAPTER 10 ELECROSTATICS REPARED BY MRS.SHITAL ONAWANE MSC.BED RAMBH MAHAVIDYLAY, NASHIK ROAD
- 2. Coulomb’s Law inVector Form: r + q1 + q2 F21 F12 r12 q1q2 > 0 q1q2 < 0 r + q1 - q2 F21 F12 r12 In vacuum, for q1 q2 > 0, q1 q2 r2 1 4πε0 r21 F12 = q1 q2 r2 1 4πε0 r12 F21 = In vacuum, for q1 q2 < 0, q1 q2 r2 1 4πε0 r12 F12 = q1 q2 r2 1 4πε0 r21 F21 = & F12 = - F21 (in all the cases) r - q1 - q2 F21 F12 r12 q1q2 > 0 q1 q2 r3 1 4πε0 r12 F12 =
- 3. q1 q2 r3 1 4πε0 r12 F12 = q1q2 r3 1 4πε0 r21 F21 = & Units of Charge: In SI system, the unit of charge is coulomb (C). One coulomb of charge is that charge which when placed at rest in vacuum at a distance of one metre from an equal and similar stationary charge repels it and is repelled by it with a force of 9 x 109 newton. In cgs electrostatic system, the unit of charge is ‘statcoulomb’ or ‘esu of charge’. In cgs electrostatic system, k = 1 / K where K is ‘dielectric constant’.
- 4. 1 emu ofcharge = c esu of charge 1 emu of charge = 3 x 1010 esu of charge 1 coulomb of charge = 3 x 109 statcoulomb 1 abcoulomb = 10 coulomb F = q1 q2 r2 If q1 = q2 = q (say), r = 1 cm and F = 1 dyne, then q = ± 1 statcoulomb. In cgs electromagnetic system, the unit of charge is ‘abcoulomb’ or ‘emu of charge’. For vacuum, K = 1.
- 5. Relative Permittivity orDielectric Constant or Specific Inductive Capacity or Dielectric Coefficient: The dielectric constant or relative permittivity or specific inductive capacity or dielectric coefficient is given by the ratio of the absolute permittivity of the medium to the permittivity of free space. K = εr = ε ε0 The dielectric constant or relative permittivity or specific inductive capacity or dielectric coefficient can also be defined as the ratio of the electrostatic force between two charges separated by a certain distance in vacuum to the electrostatic force between the same two charges separated by the same distance in that medium. Dielectric constant has no unit. K = εr = Fv Fm t
- 6. PRINCIPLE OF SUPERPOSITION Explanation 1.Considera number of point charges q1, q2 , q3 ------ kept at points A1, A2, A3,------ as shown figure. 2. The force exerted on the charge q1 by q2 is F12 The value of F12 is calculated by ignoring the presence of other charges simillarly force F13.F14 can be found using the coulombs law. 3. Total force F1 on charge q1 is the vector sum of all such forces. Statement:- When a number of charges are interacting, the resultant force on a particular charge is given by the vector sum of the forces exerted by individual charges.
- 7. Where q1,q2 q3 -------- qn are the point charges then the force F exerted by yhese charges on a tese charges q0 is given by Where rnvis a unit vector directed from the nth charge to the test ccharge q0 and r0 is the seperation between then rn= rn r0 Ftest = F1+F2+F3+-----Fn
- 8. ANSWER THE FOLLOWINGQUESTIONS 1. What is quantization of charge ? 2. What is the magnitude of charge on a electron? 3. Define a unit charge ? 4. Explain coulomb’s law in vector form? 5. State and explain principle of superposition? 6. Explain Atoms are electrically neutral ?
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