In the theory of current electricity, electrons are considered as charge carrier
ID: 2273666 • Letter: I
Question
In the theory of current electricity, electrons are considered as charge carriers to carry a current through a conductor.
The mobility ? of electrons is related to electron drift velocity by vd = ? E where E is the electric field obtained by potential difference ?V between the ends of the conductor.
(a) A length of silver wire 0.5mm diameter and 25 m long has a resistance of 2.02 ohms. Assuming one conduction electron for every silver atom, Find the drift velocity vd and electron mobility ? when 8A current flows through the silver wire.
(b) Based on the value you got for Vd above, how long you think it would take for the electrons to travel the entire length of the wire.
(c) Based on your answer for (b) above, how is that when you turn on a light switch, the light comes on almost instantaneously instead Of the time you calculated in (b)
Explanation / Answer
V = I * R = 16.16 Volts
E = V/d = 16.16/25 = 0.6464 Volt/metre
Mobility of electron = 1(m^2)/(V-s)
a) Vd = 1 * 0.6464 = 0.6464 m/s
b) T = 25/0.6464 = 38.67 s
c)
1) The electric current is flow of electrons in metal wires, (or in fluids like electrolytes). The electrons are moving in the wire at the drift velocity
v=IenA
where: I is the electric current; e is the elctric charge on the electron; n is the electron number density in the metal material of the wire; A the cross section area of the wire.
Depending on the values of I, n and A, the speed v has a typical value of several cms?1!
2) However, the cause of the motion of the electrons is the electric field, that you set in the wire when you switch on the light say, that travells along the wire at the speed of light. As the field travels along the wire so fast, it sets the electrons along the way into motion all along the wire. So it appears as if the electrons are moving very fast, when in fact they don't.