A circuit is constructed from two batteries and two wires, as shown in the diagr

Question

A circuit is constructed from two batteries and two wires, as shown in the diagram below.

Each battery has an emf of 1.6 volts. Each wire is 27 cm long, and has a diameter of 0.0007 meters. The wires are made of a metal which has 7e+28 mobile electrons per cubic meter; the electron mobility is 2e-05 (m/s)/(V/m). A steady current runs through the circuit. The locations marked by "x" and labeled by a letter are in the interior of the wire.

What is the magnitude of the electric field at location B?
EB = ____ V/m
How many electrons per second enter the positive end of battery #2?
____ electrons/s
If the cross-sectional area of both wires were increased by a factor of 3, what would the be magnitude of the electric field at location B?
new value of EB = ____ V/m

Explanation / Answer

What is the magnitude of the electric field at location C?
E = i/L = 1.6V/0.27m = 5. 92V/M

How many electrons per second enter the positive end of battery #2?
You have a mobile electron per cubic meter of 7E28. Multiply this by the volume of the wire in order to find the number of electrons.
7E28 * (0.00035^2 * pi) = 2.7E22 e
Multiply this number by the electron mobility and the electric field to find the e/s.
2.7E22 * 2E-5 * 5.92 = 3.2E18 e/s

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