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# what is electric potential? Description

##### Description: These notes go over electric potential, electric current, magnetic field, magnetic forces, induction, electromagnetic waves, and light.
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Test 3 Study Guide Saturday, November 26, 2016 9:04 PM

## what is electric potential?

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)

Gravitational

- Plates begin both

heutral

T

-

7o

100v

Ov

9ovi

COV

Pas

- - - - - 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.

units

## the electric field strength is what?

The EFS

Stecomus = 70V - 100%

lm

Use the def.

(16)(100%) - 700pC. You

10 con

=100pf am

Enc?

- 7000 kg pana - Fect ima - 7000N

Electric Current How do we make a steady current?

Tony

direction

Przcv) Gravitational Analogy

of curret

Wire

batt

rebuild the hill

2

current destroys

hill

GV 1 of meer op het

BU

wwwwwwwwwwwww

A balt B

The typical speed of the moving charges is about .1mm/s V

The (+)'s ooze through the wire

very long

A positive

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.

## how to make a steady current?

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

small &

Gravitational Analogy

www

PTL (V) If you want to learn more check out chemistry 11 class notes
Don't forget about the age old question of gsu economics

*

(SGV

small

I

small

B

wire I c

o

wire 2

A

-

O

A

butt

Sambat

tyery where

Magnetic Fields

rces

- 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

- Cancel

VIE

0

.

M

Wbatt - PE

Complete Circuit (start is end) Weng + MEstart = MEend +ThEres.forces

- Cancel

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

V:CV

f

15.5%

At=60

25%

Pa power of battery

? st: elapsed time

Mae unit azguement.

Since Fr = 13)

P=

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

ity1-20A

I- amount of current

- 20A

- 200 ra distance from current

= 1cm

2.0lm B = MFS at our location

Mee Ampere's Law

.29x109N.m

3«/0"my -4.00x10-4 N.o

201 Olm

k: Coulomb's constant

= 9 x10‘Nima c=spred of light

- 3:10 pm

=4.00-10-40

M

=400u T

Earth-sout

Force of

bar mag

1000,ut

Magnetic Forces

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

Small

East /

SPELO MEgbert - K Eend We also discuss several other topics like rus 101

-o

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

change dir.

m 9.11 2107 kg only = 2.0193 * 10 Sky m/

Po 1,0245/62m)

2.0)13x105m/ = .0522m

Induction

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

induced current

.

(Ammeter

X XXXX

it Jox

B field into page

Pulled to

wwwwwwwwwwwww

x

x

Nature always tries to resist a changing magnetic field; when it passes through a conducting loop, nature can resist

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

2nd version of

Fung

ming IY

just turned on Chad bea zivo)

S

Induced Current

- 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)

current

just turning on

Traps B field

more

- Application: The Transformer

I CA Innt I Ave I make

A g

o

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

changing

Out

Channg B

less V mort I

more V less I

V, I. - KI,

all Ave Value small-Big Big-small

Dam

SM4V

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Transmission Lina very long ~R big

millioner of paths

Les millions of bullar

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small v

moderate v "Bia V moderato 1

Big I

A

We want

CO

wire IN R

1- Big R

Voltage

A

B

-

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

N را

Induced - Electric oll Field

i

^ momentary

Current I know off)

metal

loop!

into velocity

arrowe i info speed

screen board To make an EM Wave, shake screen in SHM.

3.108 m/

EM Pulse

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

Wavelength

in meters)

10%

10%

109 1

10

10

10

104

105

106

107

10"

10"

1010 1011 1012

Size ola wavelengih

Tied

Wii Noul

HR

Coin name of wave

INFRARED

ULTRAVIOLET

11 [II

MOENWES

O

RANS

GAMMALARI

SOURCES

HR MED

active

G

STRI

FR

Frequency

106 107

108

109 100 101

102 103 104 105 106 107 108 109 109

one photon (electron volts)

10"

10"

107

106

105

104

101

102

10

1

10

10

10

10

10%

10

Microwave Generator

27 = 6.1cm 3x108m/

reception diminishes

wl distance

f= 2.45 GHz (109) Units T = 1/f = .408ns

Ammet

wall energy no energy

این ایام

اور ایم

MPST)

bint

directo

1- (x10m)(406x102)

= 12.2x10?m= 12.2 cm

nevrone 1

ur

dista spied-time ANT ECT

f= 10242 - T - 10/ycle

2-(3x100ml)( 16"/cycle)

- 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

A~.lum

un polarized

Polarized

~all energy no energy

pause

panu

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.

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