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Electrostatic Potential and Capacitance (Gcalar : SI unit volt) “Amount of work done in bringing a unit positive from infinity to the given point, V = — charge q in bringing a unit int to another Unit of P.D. is volt PD. between two points is 1 volt if 1 J of work is done in moving a positive charge of I C from one point to the other. 1 V= 1 jcc siNmct | point charge (@pherically symmetric) Electric potential due to a dipole Relation between electric field and potential E =-ve of potential gradient = — dV / dr same electric potential at F properties are : e in moving a test charge over = surface. 2. E acts always quipotential surface at every otential surfaces are close s of strong field. 4.No two es can intersect each other. Electric potential energy Amount of work done in assembling the point charges at their locations by bringing them in, from infinity. PE. of charge = Charge x Potential at the given point 2 ya P.E, of three point charges ha, 245, I | ts % uniform electric field between p and E, then urd im - pEcos0=-p.E 0°U=-pE (Stable equilibrium) °.U = + pE (Unstable equilibrium) Conductors ' The substances which allow large scale physical movement of electric charges through them ‘under an external electric field. They contain a large number of free electrons. rties of a conductor ic field is zero in the interior of > ide the conductor E is normal to the t charge in the interior of a conductor is d any excess charge resides on its e of a charged conductor, E « a. , ric field is zero in the cavity of a hollow conductor, {+ Electrostatic shielding The phenomenon of making a region free from electric field by surrounding it with a conducting sheet. charge required to increase the onductor by unit amount. Capacitance of a spherical conductor C=4ne, R, R= radius of the conductor. tial of charged conductors ht ant 4gt fotal capacitance C, +C, gh it but permits them to exert ic forces on one another. Polar are made of polar molecules. lectrics are made of non-polar Polarisation of a dielectric If the region between the capacitor plates is filled with a dielectric, the electric field due to the charged plates induces a net dipole moment in the dielectric. This effect is called polarisation which induces a field in the opposite direction. The electric field inside the dielectric decreases. The p.d. between the plates also decreases. Hence the capacitance C increases, An arrangement of two conductors separated by an insulating medium that is used to store electric charge and electric energy. of a capacitor required to be supplied to either of a capacitor to increase the p.d, he two conductors by unit amount, 4 c=4 v SI unit of capacitance is farad The capacitance of a capacitor is 1 F if 1 C of charge is transferred from its one plate to another-on applying a p.d. of I V between the two plates. ic 1F-s= =10"2 Ty IpF=l0-?F cu 2A a per unit volume in the region of Le op geet 2 teF Dielectric constant Capacitance with dielectric between the plates ~ Capacitance with vacuum between the plates a capacitor with a dielectric slab A (For t
