com www.GOALias.blogspot.com

www.GOALias.blogspot.comPhysics11. For capacitors in the series combination, the total capacitance C is given by1 1 1 1= + + + ...C C C C1 2 3In the parallel combination, the total capacitance C is:C = C 1+ C 2+ C 3+ ...where C 1, C 2, C 3... are individual capacitances.12. The energy U stored in a capacitor of capacitance C, with charge Q andvoltage V is1 1 2 1 QU = QV = CV =2 2 2 C2The electric energy density (energy per unit volume) in a region withelectric field is (1/2)ε 0E 2 .13. A Van de Graaff generator consists of a large spherical conducting shell(a few metre in diameter). By means of a moving belt and suitable brushes,charge is continuously transferred to the shell and potential differenceof the order of several million volts is built up, which can be used foraccelerating charged particles.Physical quantity Symbol Dimensions Unit RemarkPotential φ or V [M 1 L 2 T –3 A –1 ] V Potential difference isphysically significantCapacitance C [M –1 L –2 T –4 A 2 ] FPolarisation P [L –2 AT] C m -2 Dipole moment per unitvolumeDielectric constant K [Dimensionless]POINTS TO PONDER861. Electrostatics deals with forces between charges at rest. But if there is aforce on a charge, how can it be at rest? Thus, when we are talking ofelectrostatic force between charges, it should be understood that eachcharge is being kept at rest by some unspecified force that opposes thenet Coulomb force on the charge.2. A capacitor is so configured that it confines the electric field lines withina small region of space. Thus, even though field may have considerablestrength, the potential difference between the two conductors of acapacitor is small.3. Electric field is discontinuous across the surface of a spherical chargedσshell. It is zero inside and ε n ˆ outside. Electric potential is, however0continuous across the surface, equal to q/4πε 0R at the surface.4. The torque p × E on a dipole causes it to oscillate about E. Only if thereis a dissipative mechanism, the oscillations are damped and the dipoleeventually aligns with E.