# Magnitude of the electric field in a copper wire.

#### Pepjag

1. Homework Statement

In the circuit shown, two thick copper wires connect a 1.5 V battery to a Nichrome wire. Each copper wire has radius R = 7 mm and is L = 18 cm long. Copper has 8.4 × 10^28 mobile electrons per cubic meter and an electron mobility of 4.4×10^−3 (m/s)/(V/m). The Nichrome wire is l = 5 cm long and has radius r = 3 mm. Nichrome has 9 × 10^28 mobile electrons/m3 and an electron mobility of 7 × 10^−5 (m/s)/(V/m). What is the magnitude of the electric field in the copper wire? Answer in units of N/C

2. Homework Equations

$\bar{v}$$_{thin}$=(A$_{thick}$/A$_{thin}$)$\bar{v}$$_{thick}$

$\bar{v}$ = uE

E=V/L

3. The Attempt at a Solution

I plug in my known values, but I have two unknowns, the electric fields. I'm not sure how to use these equations.

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#### Simon Bridge

Homework Helper
You also know other stuff: that $2V_{Cu}+V_{Ni}=1.5V$ for example.

You also know all kinds of physics about the drift velocity, resistance, current etc. to draw on.
http://en.wikipedia.org/wiki/Drift_velocity

#### Pepjag

I had figured it out for a while now but thanks anyway. I just had to use the electron current formula and the voltage loop formula (as you stated); Plug in numbers, solve for e-field and plug in to the other equation.

#### Simon Bridge

Homework Helper
Cool - hopefully someone else stuck on a similar problem will benefit from your question ;)

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