Monday
July 28, 2014

Homework Help: Science guys :)

Posted by Zach on Wednesday, August 31, 2005 at 12:54am.

hey guys a got a few problems i need help with im really desperate for help theyre due soon online :(

1.Suppose that a constant current of 89 mA flows in a conductor.

Find the absolute value of the total charge that passes through the conductor in 3 minute(s).
Charge = ______ C

[b]b.) Number of electrons = ?

2.) A bar semiconduction material at 30 degrees Celsius has a density of 5E10 holes/cm3 and 5E10 electrons/cm3. The hole charge is 1.6E-19 C, and the charge of an electron is -1.6E-19 C.

The cross sectional area of the bar is [/B]9 cm2. When a voltage of 7V is applied across the ends of the bar, the holes travel with average velocity 8000 cm/s and the electrons travel in the opposite direction with velocity -100000 cm/s.

a) What is the flow rate of holes? ___ holes
b) What is the flow rate of electrons? __
c) What is the current? The current is referenced in the direction of the flow of holes ___ A

LAST ONE 3.) You wish to make 11ohm electric heating coil from 18 gauge nichrome wire. The resitivity of nichrome is 1E-4 ohm-cm and the cross-sectional area of 18 gauge wire is 0.001276 in2.

What length of wire in meters is needed? ___ meters


THANK YOU very much its very appreciated <3


1. Q (Coulombs) = [Current(Amps)]*180 s
(b) Divide Q by the electron charge e=1.6*10^-19 C to get the number of electrons.

2. a) hole flow rate = (hole density) * (hole drift velocity) * (bar area)
b) electron flow rate = (free electron density) * (electron drift velocity) * (bar area)
c) current = sum of (a)and (b), multiplied by the electron charge e.

3. R (ohms)= Length) * (resistivity) /Area

L = (R* Area)/(resistivity)
You must convert the area in in^2 to cm^2 before using the formula above. The answer will be in cm. Then convert that to meters by dividing by 100 cm/m

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