Edexcel AS Physics Unit 2
Waves
Frequency
The number of oscillations per unit time
Measured in Hertz (Hz)
Period
The time taken for a point on a ave to move throu!h one complete oscillation
Measured in seconds
T"
$mplitude The ma%imum displacement of a ave from the equilibrium position
Measured in metres (m)
Wavelen!th& ' The distance beteen to correspondin! points on a ave
Measured in metres (m)
Trou!h The minimum or loest point of a ave in a cycle
rest The ma%imum or hi!hest point of a ave in a cycle
Mechanical aves
Waves hich require a medium to travel throu!h *!* ater aves& sound aves and seismic aves
Propa!ation
The direction of travel of a ave
ontinuous aves
Waves ith an in+nite len!th
Wave trains
Waves ith a +nite len!th
Pulse
,ery short ave motion
Transverse aves -isturbance occurs perpendicular to the propa!ation of the ave
.on!itudinal aves -isturbance occurs parallel to the propa!ation of the ave
Wave fronts
$n ima!inary surface that moves ith a ave
Wave speed (ms/0)
Wave speed" Frequency (Hz) % Wavelen!th (m)
, " 1'
2ays The direction in hich the ener!y of a ave is travellin!
.ines hich pass throu!h ave fronts at 345
lectroma!netic spectrum The ran!e of electroma!netic aves listed accordin! to their ori!ins and properties
2adio aves& Microaves& 6nfrared& ,isible li!ht& 7ltraviolet& 8/2ays and 9amma
lectroma!netic aves Waves consistin! of oscillatin! electric and ma!netic +elds (vectors) that are perpendicular to each other and to the direction of movement of the ave ener!y Travel at : % 04/; ms/0 in a vacuum ner!y is transported as photons Transverse
2adio aves
Wavelen!th " <04cm ;
04
Frequency beteenelectrons 04 and 04 m =ri!in " " =scillatin! -etection " 2adio aerials Properties " 2e>ected by ionosphere& easily di?racted 7ses " ommunication& 2adio astronomy
Microaves
Wavelen!th " @eteen 04cm and 04mm 04
Frequency 04 Hz =ri!in " " Ma!netrons -etection " Tuned cavities Properties " 2e>ected by metals& absorbed by metals 7ses " ommunications& cookin!
6nfrared
Wavelen!th " @eteen 0mm and A44nm 0B
Frequency Hz =ri!in " " Hot04 bodies -etection " Photo!raphy& heatin! e?ect Properties " mitted by all bodies above zero Celvin& penetrates fo! 7ses " Datellite surveyin!& T, controls
,isible li!ht
Wavelen!th " @eteen A44nm and E44nm 0E
Frequency Hz electron de/ =ri!in " " Hot04 bodies& e%citation -etection " ye& photo!raphy Properties " olour 7ses " Di!ht& communication
,isible li!ht spectrum 2ed li!ht (B4/AG4nm& E44/E;ETHz) =ran!e li!ht (G34/B4nm& E;E/G4;THz) ' ello li!ht (GA4/G34nm& G4;/GBTHz) decrease 9reen li!ht (E3G/GA4nm& GB/4THz) s& 1 increase @lue li!ht (EG4/E3Gnm& 4/;THz) s 6ndi!o li!ht (EB4/EE4nm& A0G/GTHz ) ,iolet li!ht (:;4/EG4nm& ;/A;3THz)
Remember: Richard Of York Gave Battle In ain
7ltraviolet Wavelen!th " @eteen E44nm and 0nm Frequency " 04 0GHz =ri!in " Mercury lamps& electron de/ e%citation -etection " Photo!raphy& >uorescence& solid state detectors Properties " auses skin cancer (ionisation)& absorbed in upper atmosphere 7ses " Food sterilisation& sun beds
8/2ays Wavelen!th " @eteen 0nm and 0pm Frequency " 04 0;Hz
=ri!ininner " 8/2ay tube& de/e%citation of electrons -etection " Photo!raphy& >uorescence Properties " Hi!h penetration& health hazard 7ses " -ia!nosis& radiotherapy& astronomy
9amma rays Wavelen!th " @eteen 0pm and 0fm Frequency " 04 B4Hz
=ri!in decay 9M counter& -etection " Iuclear " Photo!raphy& scintillation counter Properties " ,ery hi!hly penetratin!& health hazard 7ses " -ia!nosis& radiotherapy
Duperposition When to or more aves meet& the total displacement at any point is the sum of the displacements that each individual ave ould cause at that point
6nterference $n e?ect that occurs hen to or more aves overlap to produce a ne ave pattern (chan!e in amplitude)
6nterference patterns provide evidence for the ave nature of li!ht
onstructive 6nterference The interference that occurs hen to or more aves meet at a point such that the resultant displacement
is !reater than the lar!est individual displacement @ri!ht bandsJ loud sounds
Ma%ima
6n phase& n'
-estructive 6nterference The interference that occurs hen to or more aves meet at a point such that the resultant displacement is less than the lar!est displacement
Waves must have same ' or 1 and the same amplitude
$ntiphase& (nKL)'
-ark bandsJ no sound
Minima
Polarisation 7npolarised ave" aves oscillate in many planes
Polarised ave " aves oscillate in one plane only
Polaroid +lter only enables aves oscillatin! in one plane to pass throu!h
Filters at 345
-oppler ?ect The chan!e of frequency of a ave due to relative motion beteen the source and the observer
2esonance
$ phenomenon thatan occurs hen the to frequency at hich obect is made vibrate (the forced frequency of vibration) is equal to the natural frequency of vibration
-ampin! ner!y is lost due to friction beteen the oscillatin! body and the particles in the air
The amplitude of oscillations decrease ith time
The hi!her the dampin!& the faster the oscillations ill reduce in size
Dimple harmonic motion
The motion of obect such acceleration is an proportional tothat its its displacement from a +%ed point and is alays directed to that point
0st Harmonic
Bnd Harmonic
:rd Harmonic
Dtationary (standin!) ave $ ave in hich the vibrational ener!y is stored& rather than transmitted
Iode $ point on a standin! ave here the amplitude vibration is zero or a minimum
$nti/node $ point on a standin! ave here the amplitude of vibration is ma%imum
Tension
Hi!her tension increases frequency (hi!her pitch) ,"
, " ave speed (ms /0 ) T " tension (I) M " mass per metre of the strin! (k!m /0 )
Phase di?erence $ measure of ho much one ave leads or la!s behind another ave
Measured in de!rees or radians
*!* osine curve la!s behind the Dine curve by a phase difference of 345 (NJB rad)
-i?raction The spreadin! out of a ave as it passes throu!h an aperture (!ap)
Ma%imum di?raction occurs hen the size of the aperture is similar to the avelen!th
2efraction The chan!e of direction of a ave as it passes the boundary beteen to media
$s the ave refracts& ave speed and avelen!th chan!es
Frequency of the ave doesnOt chan!e
DnellOs .a
n"
n1sinθ1=n2sinθ2
n " refractive inde% i or θ1 " an!le of incidence
r or θ2 " an!le of refraction
2efractive inde%& (n or )
onstant for a medium
DnellOs laQ n "
n"
*!* nair " 0*4 nater " 0*::
ritical an!le&
The an!le of incidence for the denser medium for hich the an!le of refraction is 345
"
sin/0
R
<
2ay is refracted
R
"
2ay travels alon! boundary
R
<
Total internal re>ection
i
i
i
2edshift The avelen!th of li!ht emitted from a star !ets shifted toards the red end of the spectrum if the distance travelled by each successive ave increases
6f the distance travelled is less& the avelen!th !ets shifted to the blue end
vidence for the e%pansion of the universe
lectricity
The lectron
Fundamental particle (lepton)
har!e " /0* % 04 S:E
Mass " 3*00 % 04/:0 k!
Found in orbitals surroundin! the nucleus of an atom
Potential -i?erence The electrical ener!y per coulomb transferred beteen to points in a circuit
Measured in volts (,)
lectromotive Force The ener!y supplied per unit coulomb to the circuit by the cell
Measured in volts (,)
2esistance 2 The ratio of the potential di?erence across a component and the current >oin! throu!h it
2",J6 aused by collisions beteen metal ions and electrons
Measured in ohms ()
-ependent on the metalOs len!th& cross/sectional area and resistivity
Micro meter $ device used to measure very small distances
-iameter of a ire
Ieed to measure at multiple points alon! ire diameter sli!htly varies
Multimeter $ device used to measure resistance beteen to points on a metal ire
2esistivity U
2"UlJ$
2esistance" coeVcient of resistivity % len!th of metal cross/sectional area
Measured in m
onstant for a material
6nternal 2esistance& ,r The resistance to a movement of char!e (current) ithin an electrical poer source
,r" /,
,r " Potential di?erence across internal resistance (lost voltsX) " lectromotive force , " Terminal potential di?erence
6"YZJt
6 " urrent (amps)
Z " har!e (oulombs)
t " time (seconds)
6"navq
6"current (amps)
n" number of char!e carriers per unit volume
v"drift velocity (ms/0 )
q" electron char!e (0* % 04 /03 )
ner!y Transferred (W) ner!y transferred " char!e % potential di?erence
W"Z,
Measured in oules
Work done
The total amount of ener!y transferred
Work done" Poer % time
Poer
" ,olta!e % current
Work done
" ,olta!e % current % time
Deries ircuits
2 T " 20 K 2B urrent is the same for each component in the circuit Potential di?erence increases 2esistance increases
Parallel ircuits 0"0K0 2T 20
2B
2T " (202B) (20K2B)
Total current is shared beteen the components omponents have the same potential di?erence @ulbs in parallel E% bri!hter than in series less resistance
Potential divider
To calculate ***
Step 1: alculate the ratio of the resistances
Step 2: Multiply by its correspondin! resistance ration
Filament lamp •
•
•
•
•
•
Ion/ohmic urrent metal +lament temp* Metal atoms vibrate faster and further from initial positions More collisions 2esistance (!radient increases)
Metallic onductor (at constant temperature)
•
•
=hmic , 6 (at constant temp*)
Demiconductor diode •
•
•
•
Ion/ohmic Has B resistances dependin! on polarity (ay it is connected) Forard direction" lo resistance 2everse direction " hi!h resistance
Thermistor •
Temp*
•
urrent
•
•
har!e carrier density 2esistance
.i!ht/dependent resistor (.-2) •
e/ released hen li!ht shines on it
•
har!e carrier density
•
urrent
•
2esistance
•
-ark " no e%tra e/ available hi!her resistance
Poer dissipation P The rate at hich ener!y is transferred to an element in a circuit
Measured in Watts (W)
P",6
Where[
P"6B2
P " Poer (W) 6 " urrent ($) , " ,olta!e (,)
P"
Circhho?\s 0st .a The total current into any point in a circuit is equal to the total current out of that point
*!* 60K6B"6:K6EK6G
Circhho?Os Bnd .a The sum of the potential rises and falls around a closed path in a circuit is zero
The Iature of .i!ht
@lack body
$ perfect emitterradiation and absorber of electroma!netic
PlanckOs constant& h h" *: % 04/:E ]s
Where[
" h1
" hc '
'" h " h p mv
1 c
" Photon ener!y (e,) " frequency (Hz) " speed of li!ht (: % 04/; ms/0) ' " de @ro!lie Wavelen!th (m) p " momentum (k!ms/0) m " mass of an electron (3*0 % 04/:0 k!) v " velocity of
Ma%imum kinetic ener!y& LmvBma% 6ncreases ith frequency
LmvBma%" h1 ^ _
h1 " photon ener!y
_ " ork function of metal
Photoelectric e?ect The eection of an electron from a metal surface hen the surface is irradiated ith electroma!netic radiation of a hi!h enou!h frequency
9old .eaf lectroscope `inc plate !iven electrostatic char!e lectroma!netic ave ith a frequency above the threshold frequency or ener!y above hits the plate& electrons emitted The !old leaf loses char!e so ill fall
Threshold frequency 1
The minimum frequency required photoelectrons to be emitted fromin a order metal for surface
Frequency of incident radiation
Increases kinetic energy of emitted electrons
This is because the energy of the photon is increased 1"
1"
Where*** 1" frequency of incident radiation (Hz) '" avelen!th of incident radiation (m) c" : % 04/; (ms/0) " Photon ener!y (e,) h"PlankOs constant (*: % 04/:E ]s)
6ntensity of incident radiation The hi!her the intensity of a beam of li!ht& the more electrons are emitted from a metal surface
This is because more photons are hittin! the metal per second
6ntensity has no e?ect on the speed of the photoelectrons emitted& only increases the number of electrons emitted
6ntensity $mplitude B (for a sinusoidal ave)
Work Function _ The ener!y required to release an electron from the surface of a metal
onstant for a metal Where[
_ " h1 h " PlanckOs constant ]s) 1" threshold frequency
(*: % 04/:E (Hz)
Dtoppin! Potential& e,stop
,olta!e required perofunit coulomb to stop outard movement electrons emitted bythe photoelectric action*
LmvBma% " e,stop
ner!y levels
lectrons occupy discrete ener!y levels
9round state" loest ener!y level an atom can occupy (n"0) ner!y is transferred in the collisions When they !ain ener!y& electrons move to hi!her ener!y levels then return to their !round state by emittin! photons "hf
ner!y level dia!rams Dhortest avelen!th hi!hest ener!y photon ner!y shon as ne!ative as ener!y must be provided in order for a electron to move to a more e%cited state
*!* ner!y level dia!ram for hydro!en* Dhortest avelen!th (in red)& lon!est avelen!th (in !reen)
2adiation Flu% (6ntensity) The amount of ener!y landin! on an area per unit time
F"
F" 6ntensity (Wm /B )
P"Poer (W)
$"$rea (mB )
Photovoltaic Vciency Vciency " useful ener!y (or poer) input % 044 total ener!y (or poer) input
lectronvolt
The ener!y transferred hen an electron travels throu!h a potential di?erence of one volt
0e," 0* % 04/03
$bsorption and mission spectra The spectrum of frequencies of electroma!netic radiation emitted or absorbed due to an atom\s electrons makin! a transition from a hi!h ener!y state to a loer ener!y state To typesQ continuous and line