In a copper wire electrons are bouncing around but have no net motion along the
ID: 1345594 • Letter: I
Question
In a copper wire electrons are bouncing around but have no net motion along the wire when there isn't a battery attached to it. Their kinetic energy is typically 1.5*10^-21 J. (A) Calculate the average speed of electron.
An electric field of 0.02 V/m is applied across a copper wire and there is net motion of the elctrons along the wire. The collision time for the electrons in a wire is on the average 2.8*10^-14 in copper. (B) Calculate the drift velocity.
(C) How is it that when a switch is closed in a room that a light bulb lights almost instantaneously?
(D) In a closed circuit with a battery the drift speed remains constant even though there is an electric field supplying energy to the wire. Where does the electron energy go and how is this related to resistance in a wire?
Explanation / Answer
keinetic energy K=1.5*10^-21 J
electric field E=0.02 v/m
collission time T=2.8*10^-14 sec
A)
kinetic energy K=1/2*m*v^2
1.5*10^-21=1/2*9.1*10^-31*v^2
avg speed v=5.74*10^4 m/sec
B)
drift veleocity vd=e*E*T/me
vd=(1.6*10^-19*0.02*2.8*10^-14)/(9.1*10^-31)
vd=9.85*10^-5 m/sec
C)
if a switch is closed drift speed remains same vd=9.85*10^-5 m/sec
D)
here,
due to collission the some part of the electic energy is converted into heat energy,
heat energy,H=i^2*R*t
and loss of heat enegry depends on the Resistance