Lecture (7) Electric Current PDF

Lecture (7) Electric current - conductor: In any conductor there are a number of free electrons but no current flow because the free electron move a random motion The random motion of the electrons cancel each other which means no net flow of charges.  In order to make a net flow of ch...

Lecture (7) Electric current - conductor: In any conductor there are a number of free electrons but no current flow because the free electron move a random motion The random motion of the electrons cancel each other which means no net flow of charges.  In order to make a net flow of charges, the charges must move with an average drift velocity 𝑣𝑑 This can made by apply an electric potential across the two ends of the conductor. When apply voltage An electric field E will be exist in direction from (+ve) end to (-ve) end as shown in figure. The negatively charged electrons will move in opposite direction of the electric field E  When an electron move it leave a positively charged hole as shown in figure. The hole will move in opposite direction of electrons i.e in the direction of E.F. Motion of hole cause what is called conventional current. the quantity of charge dQ which flow per unit volume V of the conductor: dQ = n dV e , e= charge of electron=1.6 ∗ 10−19 𝐶 , dV = l dA , A: the cross section area of a conductor dl: the length of a conductor dQ = nAle  Electric current is defined as the rate at which charges dQ flows through a conductor in a time t 𝑑𝑄 𝑑𝐼 = (unit:C/sec= Ampere) 𝑑𝑡 𝑛 𝑙 𝑑𝐴 𝑒 d𝐼 = = nA𝑣𝑑 𝑒 𝑑𝑡 𝑣𝑑 : drift velocity 𝑑𝐼 n𝑣𝑑 𝑒 dA 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑑𝐽 = = = n𝑣𝑑 𝑒 𝑑𝐴 𝑑𝐴