Test 3 Study Guide Saturday, November 26, 2016 9:04 PM
Electric Potential Electric Potential (PTL) is electric potential energy per unit charge; voltage is a difference in electric PTL.
The units of PTL are J/C (instead of J/kg). J/C are called Volts (V) -> Alessandro Volta (battery in 1800)
First we must "build the hill"
real PTL (V)
- Plates begin both
© Analogy smo low
- - - - - OV 30 V - 20v Touch-battery moves electrons from right plate to left plate until a 70-volt "hill" has been built.
It takes work to carry positive charges "up the hill" from
negative to positive plate. The Electric Field Strength (EFS) is the amount of electric force per unit charge; the EFS is also the "steepness" of the PTL "hill" in units of V/m.
Stecomus = 70V - 100%
Use the def.
(16)(100%) - 700pC. You
- 7000 kg pana - Fect ima - 7000N
Electric Current How do we make a steady current?
Przcv) Gravitational Analogy
rebuild the hill
GV 1 of meer op het
A balt B
The typical speed of the moving charges is about .1mm/s V
The (+)'s ooze through the wire
Our hypothetical moving positive charges go "down hill as they move through a wire, but they do not go faster because of resistive forces matching the driving electric force so that the charges move at constant speed. We also discuss several other topics like phi 1020 class notes
The current (I) is the rate of charge flow in units of C/s going past any location in the circuit in a simple circuit (one path) the current is the same everywhere.
The units of C/s is called amperes (A) -> Andre-Marie Ampere (~1825) Typical currents are .1-1 AMPS
For a given path through a given piece of metal, the current is big when the "hill" is big.
Amount of current is proportional to the size of "hill" (i.e. the voltage) Ohm's Law: I=1/R(V) or V=IR or R= V/1
Units of Rare volts/amps = ohms ( -> omega)
Circuit with 2 wires and bulb
wire I c
- Cancel - -
Wire + Fil. (C->D for example) Weng + MEstart = MEend +ThEres.forces KEndant PE stond Klark+ PEod * There lice
by choice PĘ = The Erfories Fil. gets hot
- wires get warm Battery (A->B) Weng + MEstart = MEend +Theres.touses Watt + T Estond + PE por = TEank + Pferd
Wbatt - PE
Complete Circuit (start is end) Weng + MEstart = MEend +ThEres.forces
Wonth = Theres forces
(+ light in Fl)
Suppose a 6V battery is driving a .5A current in a simple circuit. A. At what rate is the battery doing work? B. How much work is done in 1 minute?
V= battery voltage
V: ZV -6 V
= 64 I= amount of current
Pa power of battery
? st: elapsed time
Mae unit azguement.
Since Fr = 13)
VI =(6V8.54) :34", = 3%
= 1 min
W: work done in 60s
Mor unit argument
W = P.at
3W (60) - 1807 - 180J
Currents create magnetic fields; the magnetic field lines surround the current.
Electric field lines start on positive charges and end on negative charges.
Magnetic field lines (MFL) make loops around currents. Predict with "Grab the Wire". Magnetic field strength (MFS) proportional to 1/r We also discuss several other topics like phys 1110 cu boulder
B = 2k/c2*l/r Ampere's Law
The atoms themselves are little current loops. Due to a current Find the MFS at a point 1cm from a 20A current
I- amount of current
- 200 ra distance from current
2.0lm B = MFS at our location
Mee Ampere's Law
3«/0"my -4.00x10-4 N.o
k: Coulomb's constant
= 9 x10‘Nima c=spred of light
- 3:10 pm
The magnetic force (on a moving charge) is perpendicular to the magnetic field and also perpendicular to the velocity of the moving charge.
Lorentz's Magnetic Force Law -> Henrik Antoon Lorentz (for negative charges use your left hand; positive-right hand)
On an electron beam mo:9.11x10-9kg 90 = 1.610"C len v~o
SPELO MEgbert - K Eend We also discuss several other topics like rus 101
PE start = KE and -neg 300v} off
191V='amov? B field QN: 1.0265*10 m/s Pre nego se poslate >= 1.0265*10 m/s - > Lorenta's Law
11204T Tmag for the Frag = I alwB 1812
- amounts magique
Frog 11.6-10°"CI (1.0265-10%>% X 1120x1067)
= 1.89956*10*"C. ZAMAN 2nd Low Frer-ma -> Fact 1.83 956+101N
m 9.11 2107 kg only = 2.0193 * 10 Sky m/
2.0)13x105m/ = .0522m
Three Induction Experiments
1. Move a wire (a part of a loop) in a magnetic field. An induced current while moving. -> Lorentz's Mag Force Law Don't forget about the age old question of dep3053 uf
B field into page
Nature always tries to resist a changing magnetic field; when it passes through a conducting loop, nature can resist
-> Faraday's Law of Induction
2. Move a magnet into (or out of) a loop of wire. Induced current while moving (more turns => more inductive effect)
3. Start or stop a current in an adjacent loop (replace the moving magnet with current loop and switch). Induced current while
adjacent current starts or stops. -> Faraday's Law of Induction
2nd version of
just turned on Chad bea zivo)
- Cu Ring
s Nature resists by creating an induced current to fight the changing B Field. Driven with an Induced Electric Field (this makes loops like the B field)
just turning on
(had been zero)
Traps B field
Faraday's Law of Induction
- Application: The Transformer
I CA Innt I Ave I make
turns =) more induced effect
=> more induced voltage to the For Ideal
~95% 7- Changing Induced I Power In-Power
light the 1 bulb
for Ideal se
less V mort I
more V less I
V, I. - KI,
all Ave Value small-Big Big-small
Transmission Lina very long ~R big
millioner of paths
Les millions of bullar
moderate v "Bia V moderato 1
wire IN R
1- Big R
CELD Wirel A
Electromagnetic Waves Traveling Electromagnetic (EM) Waves carry energy away from a vibrating collection of charges; no medium is required; light is an EM Wave.
Maxwell's Argument Simplified
Induced - Electric oll Field
Current I know off)
arrowe i info speed
screen board To make an EM Wave, shake screen in SHM.
Light: Wave or Particle Traveling Electromagnetic waves carry energy away from a vibrating collection of charges; no medium is required; light is an EM wave; all EM waves have both wave and particle properties.
To make an EM wave, wiggle a screen in SHM.
THE ELECTROMAGNETIC SPECTRUM
1010 1011 1012
Size ola wavelengih
Coin name of wave
109 100 101
102 103 104 105 106 107 108 109 109
one photon (electron volts)
27 = 6.1cm 3x108m/
f= 2.45 GHz (109) Units T = 1/f = .408ns
wall energy no energy
= 12.2x10?m= 12.2 cm
dista spied-time ANT ECT
f= 10242 - T - 10/ycle
- 3x10?m = 3x10 m = 3um
in the wires
free @ speed = .1 mm/s range of motion? dist=spred time
range -l10mA) 6.204x10-3)
= .204 x10 m - 20.4x10 m - 20.46
The intensity of an EM wave decrease as you get further from the source because the farther from the source, the wave energy is spread out over a larger area.
Light is an EM Wave
~all energy no energy
Light from an incandescent light bulb is "unpolarized" because visible light comes from atoms; there are a large number of atoms so the light from the bulb includes some light polarized in every possible direction.