Ch – 28 Current and Conductivity . Current: Motion of charge through a conductor. How do we know there is a current?. Charge carriers.
Moving sea of electrons
i = Ne/∆t
Ne (number of electrons) = i ∆t
Ne = nV where V is the volume of the wire (A ∆x) and n is the conduction electron density (on the order of 1028 electrons per m3)
∆x = vd ∆t, therefore:
Ne = nAvd ∆t
Ne/∆t = i = nAvd
i is proportional to r2vd. Changing r has more influence than changing v by the same amount
1.0 x 1016 electrons flow through a x-section of silver wire in 320 μs with a drift velocity of 8.0 x 10 -4 m/s. What is the diameter of the wire?
9.26 x 10-4 m
An electron current is a non-equilibrium motion of charges sustained by an electric field
E depends on the difference in the charge on the two rings. The E fields of a and c are zero. The difference is the greatest for the rings of d.
ή = 5.1 x 10-12 C/m2
In an ionic solution, 5.0 x 1015 positive ions with charge +2e pass to the right, while 6.0 x 1015 negative ions with charge –e pass to the left. What is the current in the solution and what is the direction of the E field?
2.56 mA (milliamps).
E field is to the right
The current in a wire at time t is given by the expression: I = (2.0 A)e-t/(2.0μs) where t is in μs and t>=0.
J = I/A = nevd (A/m2)
The current in wire is doubled. By what factor do the following change?