Write definition of electric field intensity. Obtain an expression for electron force and electric pressure on the surcharge of a charged conductor. Draw necessary diagram.
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Solution
Electric field intensity : It is the strength of an electric field at any point. It is equal to the electric force per unit charge experienced by a test charge placed at that point. The unit of it i s volt/meter or Newton/ Coulomb.. Every element of a charged conductor experienced a normal mechanical force. This is the result of repulsive force from similar change present on the rest of the surface of the conductor. Consider a small element ds on the surface of a charge conductor. if σ is the surface density and the charge carried by the element ds be dq. Consider a point P just outside the surface near the element ds. The electric intensity at a point P is given by E=σ∈o The direction of the intensity is normally outwards. The intensity made up of two components →E1 due to the small change dq present on the element ds. →E2 due to the remaining charge present on the rest of the surface of the conductor. Hence at P,→E1+→E2=σ∈o * Now consider a point Q inside the conductor the electric field {E_l} and {E_2} at this point are oppositely directed. However, electric intensity inside a changed conductor is zero →E1−→E2=0 →E1=→E2 Substituting for E1 in eq.(3) we have 2E2=σ∈o;E2=σ2∈o Here E2 is the electric field due to the charge on the rest of coductor. Hence repulsive force experienced by elements ds carrying dq to is given by →f=→E2.dq F=σ2∈odq f=σ2∈o.σ.dq F=sigma22∈o.dq The electric pressure on surface ds will be pressure=forceArea σ22∈odsds P=σ22∈oN/M2