Chapter 23
Solutions to Class Work and Misc. Notes
You will get a charge out of these shocking factoids...
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•
•
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There are only two kinds of charge.
Ben Franklin defined them.
Charge is conserved.
Charge is quantized.
lel = 1.60219E­19 C
1 Coulomb of charge = 6.3E18 electrons
q
q
m
m
G
k
Fg =
F
e=
2
2
R
R
ke
1
=
4πεo
ke=
The Permittivity of Free Space
8.8542E­12 C 2/Nm2
8.9875E9 Nm2/C2
*When using Coulombs constant... charges are measured in Coulombs and distances in meters.
Field
Fe
E=
qo
E=
Fe = E qo
kq
R2
Fe = E qo
Mole Pop Quiz
An overzealous reporter from a tabloid newspaper working on a tip from a prominent L.A. plastic surgeon, sets out to prove the Cindy Crawford's famous mole (on her lip) is fake. He stages an elaborate sham. He poses as a replacement for Cindy's regular make­up artist. While plucking a few stray nose hairs he grabs her mole with tweezers and yanks with all his might. The mole breaks loose and the reporter is out the door with the sample in hand. He takes the sample to a friend in the chemistry field and has her analyze the sample using sophisticated chromatographic techniques. The mole sample weighs in at .02 grams, and proves to be made of vinyl chloride (C2H3Cl).
Your Job is to determine the following (show your work!)...
a) What is the formula mass (g/mole) for vinyl chloride?
b) How many moles of vinyl chloride molecules were in the sample?
c) How many moles of carbon atoms were in the sample?
d) How many atoms of carbon were in the sample?
e) If the electrons from half of the carbon atoms in the sample were removed, what would the strength of the electric field be at a distance of 1cm from the surface of the mole?
1. 2.
Coulombic Craziness
Finding E­Field Near Chaaaaaaaaaaage Distribuuuuuuuuuuuutions.
Step 1: Apply coordinate system and check for symmetry.
Consider the Following!
Step 2: Use Coulombs law to define dE in terms of dq.
Step 3: Set up integral for E with limits.
Step 4: Substitute for dq in terms of λ,σ, or ρ.
Step 5: Integrate and evaluate at limits.
Step 6: Replace λ,σ, or ρ with Q/L, Q/A, or Q/V. What about a chaaaaaaged
rod?
How bout a hooooooooooooooooooooooop of charge?
I wonder if a rolling disc of chaaaage
beats a chaaaged hoooooop?
Rodney Get's Charged Up and Bent Out of Shape
OUCH!
Find the force that an electron would feel if it were placed at the origin of the axes shown in terms of only Q (The total charge on Rodney), L (The length of Rodney) and fundamental constants.
Types of Problems in Ch. 23
• Transfer of charge causes strong forces (stoichiometry)
• Systems of point charges create superimposed E­field
• Distribuuuuution of charge creates E­field
charged rod (only points off of end)
hoop of charge (only along central axis)
part of a hoop / bent rod (only at focal point)
• Motion of charges projected into E­field (mimics projectile motion in gravity field)