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PHY 303L
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Jack Turner
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Final

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University of Texas at Austin

Physics

PHY 303L

Jack Turner

Fall

Description

Constants
Coulomb’s Constant ❑ ❑ ❑❑ ❑
speed of light ❑ ❑
Chapter 14: Electric Field
Coulomb’s Law for point charges
∣ ❑ ∣❑ ❑
❑ ❑❑
Like charges repel, unlike charges attract
Force acts along a line
Electric force is much greater than the Mechanical force
Electric Field and Electric Force
Apoint charge is not affected by its own Electric Field
Electric Field on a point charge
❑
❑
Direction of Field depends on direction of r and sign of q
Electric field in a uniformly charged sphere is 0
Electric field outside of a uniformly charged sphere is same
Don’t forget about superposition
Electric field of a dipole along the vertical axis
❑ ❑ ❑ ❑❑ ❑
❑ ❑
where r is the distance between the observation point and the center of the dipole
and s is the distance between the proton and electron
Electric field of a dipole along the vertical axis if r >> s
❑
❑
Electric field of a dipole along the horizontal axis
❑ ❑❑❑ ❑ ❑
Electric field of a dipole along the horizontal axis if r >> s
❑
❑
Electric Dipole Moment
Electric fields of a positively charged particle radiate outward while the electric field of a
negative particle radiates toward the particle
Electric field around a dipole is exactly what you would expect by putting that ^ and
superposition together
Chapter 15: Electrics Fields and Matter, what a dumb title
Zero net charge does not mean there is no charge
Conservation of charge is a thing. Charge can move between a system and its surrounding but
cannot be created or destroyed.
Conductors have freely moving electrons.
E = 0 inside a conductor once it reaches equilibrium
Drift Speed
where v is the average drift speed of a mobile charge
and u the the mobility of the charge
Insulators have polarized atoms that cannot move freely. This happens almost instantaneously. Polarization means the electron cloud moves over
Electric fields cause induced dipoles
Polarizability
where p is the dipole moment
is the polarizability
Momentum Principle
❑ ❑ ❑ ❑❑ ❑
You can discharge a charged objects by grounding (connecting with the Earth), or contact with
another surface so that the charges may move between the two objects. You can discharge the
tape (insulator) by rubbing it with your hand because there are mobile charges on your skin.
Force between and point charge and a neutral atom
❑ ❑ ❑ ❑
Chapter 16: Electric Field of Distributed Charges, May want to re-read
Uniformly charged thin rod
Expression of Electric field due to one piece
then
❑ ❑ ❑
❑ ❑ ❑ ❑❑ ❑
❑ ❑ ❑ ❑
Find the summation and integral
❑ ❑
❑ ❑ ❑ ❑
❑ ❑ ∫❑❑ ❑ ❑ = √❑
❑
if r (or x) >> L then
❑
❑
if L >> r (super long rod)
Hollow Cylinder for L >> R
E = <0, - * 4Q/3 , >
Uniformly Charged Thin Ring
Due to One piece
❑ ❑ ❑ ❑
❑
After integrat∫ng❑ ❑
❑
❑ ❑ ❑❑ ❑
if z >> R
❑ ❑
E is zero at the center of the ring
Uniformly Charged Disk
Due to one piece
❑ ❑ ❑ ❑
❑ ❑ ❑ ❑ ❑
After integration
❑ ❑ ❑ ❑
Approximation if z << R
E = (Q/A) / 2
Field is nearly independent of distance (meaning if 0 << z << R use the same formula)
Two Uniformly Charged Disks: Capacitor
Fringe field (just outside plates)
Uniformly charged hollow sphere
❑ ❑ for r > R
for r < R
Uniformly❑charged solid sphere
❑ for r > R
❑ ❑ for r < R
With multiple shapes use superposition
Chapter 17: Electric Potential
Electric Potential is the potential energy per unit charge
❑ ❑
Work-Energy Theorem
❑ ❑
❑ ❑
Electric Potential
❑ ❑
Potential Difference in a Uniform field
Electric Field is the negative derivative of the potential
path in direction of E -> Potential < 0
path opposing E -> Potential > 0
path perpendicular to E -> Potential = 0
Potential Dif❑erence in a varying field
❑ ❑ ❑❑❑
Electrical potential is independent of

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