Ouhsc - Advanced Physics Test 2

Front 1

Series vs. Parallel Circuits

Back 1

- in series, current must pass through each component in order to reach next
- in parallel, current may pass through each branch regardless of whether current is passing through any of others

Front 2

Ohm's Law Equation

Back 2

V = IR

V = voltage, I = amperes, R = resistance

Front 3

Capacitors

Back 3

- devices for storing electrical energy w/o utilizing chemical rxn
- comprised of parallel metal plates which sandwich insulating material
- when attached to current source, electrons move from negative terminal to connected plates; electrons on other plate move towards positive terminal

Front 4

When capacitor is fully charged...

Back 4

Current stops flowing

If charge isn't immediately used, it may remain charged until the charge "leaks" into air

Front 5

Laws of Magnetism

Back 5

1) Every magnet has 2 poles
2) Like poles repel, unlike poles attract
3) Strength of magnetic force equals the product of the pole strength and is inversely proportional to distance btw. them

Front 6

Types of Magnets

Back 6

Natural - earth, magnetite
Artificial - magnetized steel, alnico
Electromagnets - temporary magnets produced using electric current

Front 7

Magnetic Fields

Back 7

- also called flux lines, surround magnet
- strength is dependent on # and concentration of flux lines (always greatest @ poles)

Front 8

Flux lines ALWAYS travel in which direction?

Back 8

North pole to South pole

Front 9

Earth's Magnetic Field

Back 9

Geographical north is actually magnetic south (vis versa)

Front 10

How does a compass work?

Back 10

By magnetizing the needle, giving it poles, and suspending it so it can rotate freely

Front 11

Magnetic Measurement - Strength

Back 11

Quantified using either Maxwell (Mx) or Weber (Wb)

Front 12

Magnetic Measurement - Concentration

Back 12

Quantified using either Gauss (G) or Tesla (T)

Measures flux density

Front 13

Domains

Back 13

- within atom, orbital electrons spin, causing atom to orient itself in certain direction; causes atom to act as magnet (magnetic moment)
- when several atoms align themselves in same direction, create a domain
- the more domains that are aligned, the stronger the magnetization

Front 14

Magnetic Induction

Back 14

- occurs when material that isn't magnetized is brought near pole of magnet
- unmagnetized material's domains will be realigned by force of magnet's flux lines
- material will assume OPPOSITE polarity as a result of this

Front 15

Permeability

Back 15

- ease at which a material is magnetized; how easily are domains realigned
High Perm = iron
Low Perm = wood

Front 16

Retentivity

Back 16

- ability of magnet to retain its magnetization
- once domains align, they resist reverting back to random alignment

Front 17

"Soft" Iron Material

Back 17

- highly permeable, low retentivity
- easily magnetized, won't stay magnetized for long

Front 18

"Hard" Steel Material

Back 18

- low permeability, highly retentive
- hard to magnetize, stays magnetized for long periods

Front 19

4 Classifications of Magnetic Materials

Back 19

Nonmagnetic
Paramagnetic
Ferromagnetic
Diamagnetic

Front 20

Nonmagnetic

Back 20

- not attracted by magnet, not susceptible to magnetic induction (make good insulators)
- domains will not align
Ex. wood, glass, plastic

Front 21

Paramagnetic

Back 21

- slightly attracted by magnet
- have low magnetic permeability
- domains won't easily align
Ex. aluminum, platinum

Front 22

Ferromagnetic

Back 22

- most magnetic materials
- strongly attracted by magnet
- high permeability & retentivity
- may become permanently magnetized; domains easily align

Front 23

Diamagnetic

Back 23

- weakly repelled by magnets
- few elements exhibit this behavior
Ex. beryllium, bismuth

Front 24

Who discovered electromagnetism & when?

Back 24

Hans Oersted in 1820 (discovered a magnetic field always surrounds a conductor when current is flowing)

Front 25

When current moves through a wire a ____________ is created around it.

Back 25

Magnetic field (field is perpendicular to wire)

Front 26

When current is turned on, ______________ build around the conductor

Back 26

Flux lines

Once current @ peak, flux lines remain stable
Once current turned off, flux lines collapse & disappear

Front 27

What 2 components are required to induced electromagnetic induction?

Back 27

1) Electric current or magnet (source of flux lines)
2) Conductor (ex. coil of wire)

Front 28

Flux Linkage

Back 28

- occurs when a magnet is moved through loop of wire, and cuts its flux lines (deformed around wire)
- produces voltage/EMF [electromotive force] (potential diff. within wire); current flows through conductor

Front 29

How Induction Occurs

Back 29

When a change in flux lines causes change through loop of wire (flux linkage), produces potential diff. (voltage) across ends of loop; allows current to flow through wire

Front 30

Ways to Induce EMF (Electromotive Force)

Back 30

- conductor moves across stationary field
- field moves across conductor
- magnetic strength is varied while conductor is in field

Front 31

Magnetic Field Sources

Back 31

- anything that produces flux lines
Ex. magnet, conductor w/ current (AC or DC), electromagnet

Front 32

What affects strength of EMF (voltage)?

Back 32

1) Speed at which flux linkages occur
2) Magnetic Field Strength (increasing strength results in higher EMF) [more flux lines to be cut]
3) Angle as close to 90 degrees as possible (more flux linkages per unit area
4) Number of turns on conductor (coil) [proportional to EMF]

Front 33

Left Hand Rule

Back 33

- tells us direction of current flow induced by motion

Thumb: direction represents direction of motion of conductor
Index: represents flux line field, direction represents direction of flux lines
Middle: represents conductor; direction represents direction of induced current flow

Front 34

Motor Effect

Back 34

- if current carrying wire is placed in magnetic field, combined forces of magnet & wire will induce wire to move
- this force supplies kinetic energy needed to turn a motor
- RIGHT HAND RULE

Front 35

Right Hand Rule

Back 35

- tells us direction of motion induced by passing current through armature

Thumb: direction of motion of armature (direction we have induction of motion through)
Index: represents direction of flux lines
Middle: represents current flowing through armature; direction represents direction of current flow

Front 36

Left Thumb Rule

Back 36

- determines direction of flux line movement in relation to current flow
- thumb indicates direction of current flow
- imagine thumb as conductor

Front 37

Solenoids

Back 37

- formed by forming wire into helix (coil) & passing current through it
- takes on polar properties of magnet
- can increase its magnetic property by increasing # of coils on it

Front 38

Electromagnet

Back 38

- placing iron core within helix greatly strengthens magnetic properties of solenoid by concentrating field lines inside & around core
- can be turned on and off

Front 39

Armature

Back 39

- coil of wire that's going to interact w/ flux lines within magnetic field; can be single wire/coil
- works w/ both generator & motor
- acts as path for current flow

Front 40

Brushes

Back 40

- act as mobile contact points that allow for movement of parts
- maintains constant contact, allows for continuous current flow

Front 41

Commutator

Back 41

- specific to DC SYSTEMS
- can be used in motor or generator
- looks like split ring

Front 42

Slip Ring

Back 42

- specific to AC SYSTEMS
- allows for constant contact
- allows current flow in either direction
- can be used in generator or motor

Front 43

Requirements to have a Generator

Back 43

1) Magnetic field (source of flux [electromagnet or magnet])
2) Armature (coil of wire rotated within magnetic field)
3) Force (to turn armature)

Front 44

In order to get flux linkages, we need to...

Back 44

Move the coil of wire (armature) within field of flux lines

Front 45

4 Factors Controlling Induced Current

Back 45

1) Strength of magnetic field
2) Speed of motion between lines cut & conductor
3) Angle at which flux lines are cut
4) Number of turns on conducting coil

Front 46

What's true with every flux linkage?

Back 46

- induces voltage
- when you have voltage, you can produce current flow

Front 47

Strength of Magnetic Field

Back 47

- directly proportional
more flux lines = more flux linkages = more induced current

Front 48

Speed of Motion between Flux Linkages

Back 48

- more flux linkages per sec = more voltage, more current

Front 49

Angle at which Flux Lines are cut

Back 49

- greatest concentration of flux lines @ poles
- want to cut them at 90 degrees (getting greatest # of flux lines per unit area)
- greater angle produces greater EMF

Front 50

How many flux linkages occur for each coil of wire?

Back 50

2

For each coil, double the amount of flux linkages that occur (not more flux lines)

Front 51

DC Generators

Back 51

- armature turns within magnetic field creating flux linkages which induces current within armature (LHR); current transferred through brushes to COMMUTATOR
- use of commutator (split ring) allows current to be supplied in only 1 direction (flows in same direction [pulsating direct current])

Front 52

What happens to DC current when it's not at the poles?

Back 52

Flux linkages aren't maximized, quantity decreases --> causes voltage & current decreases --> end up w/ pulsating wave of current

Front 53

What happens at the point of 0 induction?

Back 53

Brushes hit split in commutator which produces a break in the circuit (produces open circuit)

Front 54

DC Sources

Back 54

- DC generators produce pulsating DC (EMF varies as armature passes through field)
- batteries produce constant DC (EMF maintined continuously until battery is exhausted [only have finite # of electrons that move btw poles])

Front 55

AC Generators

Back 55

- armature cuts flux lines inducing EMF
- armature moves through magnetic field inducing AC current; armature rotates so each side exchanges position, causing current to reverse
- b/c of constant contact, slip ring polarity will change w/ each half rotation
- causes current to oscillate at a rate determined by speed of armature (current flows, doesn't travel far)

Front 56

One full alternation through AC generator produces...

Back 56

Completed positive & negative waveform (each waveform induces current in different direction, opposite from each other)

Front 57

Sine & AC Current

Back 57

- the closer the armature cuts flux to 90 degrees, greater the EMF produced
- during 1 rotation the field will be cut at 90 degrees twice (one positive, one negative)

Front 58

Oscillating DC current is always on the ________ (positive/negative) side

Back 58

Positive

Front 59

Comparing DC & AC Generators

Back 59

- more efficient to transport AC current than DC
- less heat loss is attributed to AC current transport since AC current doesn't travel far
- power loss is inherent in any system, reduce it by using AC
- AC needed to operate transformers b/c they operate by induction

Front 60

Difference between Single & 3 Phase Generators

Back 60

- Single: one armature set produces one waveform per rotation
- 3 Phase: 3 armature sets at 120 degree intervals produce 3 waveforms per rotation (3x # flux linkages)
- advantage of 3 phase = at least 1 armature will be cutting the max # of flux lines at any given time

Front 61

Why are magnets curved?

Back 61

- makes waveform stay at a higher level for a longer period of time (voltage never reaches 0 because other waveforms overlap)
- can keep voltage a a higher level consistently (no variation of voltage)

Front 62

Electrical Motors

Back 62

- requires conductor w/ current (source of current flow)
- requires conductor be placed within magnetic field
- mechanical energy occurs as result of interaction btw 2 magnetic fields

Front 63

The motor conductor experiences a force that is directly proportional to...

Back 63

- its length or # of turns it's coiled into
- strength of in magnetic field
- amount of current flowing through conductor

Front 64

Wire in Motion

Back 64

- when a wire carrying current is placed in magnetic

Front 65

Direct Current Motors

Back 65

- use commutators
- reverse of DC generator

Front 66

Alternating Current Motors

Back 66

- use slip rings, causes motor effect to occur when current drops into negative half cycle

Front 67

Synchronous AC Motors

Back 67

- motor rotates @ same speed as generator supplying it
- ex. clocks & electric timers

Front 68

Induction AC Motors

Back 68

- induction by stator causes rotor to turn
- stator = even # of electromagnets arranged in a circle
- rotor = copper bars arranged around an iron core
- current supplied to successive electromagnets around stator > current induced in copper bars in rotor > motor principle creates force necessary to "push" rotor, causing rotation

Front 69

3 Factors Influencing AC Circuits

Back 69

- effective values of voltage & current --> average V or I produced in 1 alternation
- relationship between peak (I max) & effective (I eff) values
- impedance

Front 70

Formulas for Peak & Effective I (current) Values

Back 70

I eff = 0.707 x I max

I max = 1.41 x I eff

Front 71

Impedance

Back 71

- apparent total resistance in AC circuit
- symbol = Z

V = I x Z I = V/Z Z = V/I (best used for AC circuits)
[use Ohm's law for DC circuits]

Front 72

What affects amount of current induced to flow?

Back 72

Quantity of voltage

Front 73

Is a lightbulb a power source or a resistor?

Back 73

Resistor

Front 74

How many induction do we get per alternation in AC systems?

Back 74

2

1 positive, 1 negative