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G482: Electrons, waves and photons
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Define
define the coulomb The SI unit of electrical charge. 1 Coulomb of electrical charge
is the amount of charge transferred by a current of 1Amp in 1
Second
definepotential difference (p.d.); Energy transfer per unit charge from electrical to other forms.define the volt 1 Volt is equal to 1 Joule per Coulomb
define electromotive force(e.m.f.) of a source such as acell or a power supply
The energy gained per unit of charge by charges passing
through a supply. Measured in V or JC^-1
define resistance Resistance=Potential difference/current
define the ohm 1 Ohm is the resistance of a component when a potential
difference of 1 volt is produced per ampere of current.
define resistivity of a material Resistivity is equal to the product of the resistance and cross
sectional area divided by the length. =RA/l
define the kilowatt-hour (kW h)as a unit ofenergy
A unit of energy equal to 36 MJ or 1kW for 1h
define and use the termsdisplacement,amplitude, wavelength,period,phasedifference, frequency and speedof a wave
Displacement-Distance from the mean position expressed as a
vector
Amplitude- Maximum displacement
Wavelength-Distance between neighbouring identical points
Period-Time taking for one complete oscillation of a particle
Phase Difference- The fraction of a cycle between the
oscillations of two particles
Frequency-Number of waves passing a point per unit time
Speed-Distance travelled by the wave per unit timedefine the terms nodes andantinodes
Node-When the amplitude is always zero
Antinode-When the amplitude is always at its maximum
possible value
define and use the termsfundamental mode of vibrationand harmonics
Simplest pattern of movement and has the lowest possible
frequency band and the longest wavelength
Harmonics are different modes of vibration of a wave with
increasing frequency and decreasing wavelength
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G482: Electrons, waves and photons
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define and use the electronvolt(eV) as a unit of energy
1 eV is gained or lost when an electron moves through a
potential difference of 1V
Energy acquired by an electron accelerated through a p.d of
1V.
define and use the terms work
function and threshold frequency
Work function- the minimum energy required to release an
electron from the surface of a materialThreshold frequency- Frequency of a photon that will just
emit an electron from a substance without any kinetic energy
Define the term intensity Intensity is the (incident) energy per unit area per second
State
state what is meant by the term mean driftvelocity of charge carriers
The average distance travelled by the charge
carriers along the wire per second
state and use Ohms law For a metallic conductor at constant
temperature, the current in the conductor is
directly proportional to the potential difference
across itstate Kirchhoffs second law and appreciatethat this is a consequence of conservation ofenergy
Energy is conservedSum of e.m.fs=sum of voltages (total of p.ds in
a loop)
state typical values for the wavelengths ofthe different regions of the electromagneticspectrum from radio waves to -rays
Visible 600-400nm (5 x 10-7)
UV-A 400-315nmUV-B 315-260nmUV-C 260-100nm
state that all electromagnetic waves travel at the same speed in a vacuum
state that light is partially polarised on reflection
state and use the principle of superpositionof waves
When two or move waves meet at a point and
interfere, the sum of their individual
displacements is equal to the resultant
displacement.
state what is meant by constructiveinterference and destructive interference
Interference is when (two) wavesmeet/combine/interact/superpose (at a point)and there is a change in overallintensity/displacement
state that a photon is a quantum of energy of electromagnetic radiation
state that energy is conserved when a photon interacts with an electron
state that the charge carriers in an electrolyte are ions
state that the charge carriers moving through wires are electrons
Select and use (Refer to the Formula sheet)
select and use the equation Q = It
select and use the equation I =Anevselect and use the equation W = VQ
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G482: Electrons, waves and photons
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select and use the equation for resistance R =V/I
select and use the equation R = L/A
select and use power equations P = VIP = I2R andP = V2/R
select and use the equation W = IVtselect and use the equation for the total resistance of two or more resistors in series
select and use the equation for the total resistance of two or more resistors in parallel
select and use the equations e.m.f. = I (R + r),and e.m.f. = V + Ir
select and use the potential divider equation: Vout= R2x VinR1+ R2
select and use the wave equation v = f
select and use the equation for electromagnetic waves = ax/D
select and use the equation dsin = n
select and use the equations for the energy of a photon: E = hf and E = hc/
select, explain and use Einsteinsphotoelectric equation hf = + KEmax
select and apply the de Broglie equation = h/mv
Recall and use
recall and use the elementary charge e = 1.6 10-19C
recall and use appropriate circuit symbols as set out in SI Units, Signs, Symbols andAbbreviations (ASE, 1981) and Signs, Symbols and Systematics (ASE, 1995) interpret anddraw circuit diagrams using these symbols
recall and apply Maluss law for transmittedintensity of light from a polarising filter.
The intensity of light transmitted through
a polarising filter is equal to
Use and apply
use the relationships: intensity = power/cross-sectional area and intensity amplitude2use the equation: separation between adjacent nodes (or antinodes) = /2
use the transfer equation: eV = 1/2mv2for electrons and other charged particles
use the relationships hf = E1E2 and hc = E1E2/
apply Kirchhoffs first and second laws to circuits
apply graphical methods toillustrate the principle ofsuperposition
Describe
describe how an ammeter maybe used tomeasure the current in a circuit
Must be put in series to measure the current
describe Kirchhoffs first lawand appreciate that this is a
(sum of/total) current into a junction equals the (sumof/total) current out. Charge is conserved
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G482: Electrons, waves and photons
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consequence of conservation ofcharge
describe the differencebetween conductors,semiconductors and insulators
in terms of the number densityn
Conductors have lots of charge carriers (large number density)
and therefore can easily let current flow, semi conductors have
fewer free delocalised charge carriers (smaller number density)
so less current flows, it is important to note that semiconductors conduct better at higher temperatures as more
electrons break free from the atoms. Insulators have very
few/no charge carriers (number density is closer to 0) and
therefore don't let any current flow.
describe how a voltmeter maybe used to determine the p.d.across a component
The voltmeter must beput in parallel
describe the differencebetween e.m.f. andp.d. in terms of energy transfer
Potential difference is transferring electrical energy intoother forms (heat, light, sound). EMF is transferring otherforms of energy into electrical (chemical energy stored in abattery)
describe the IV characteristicsof a resistor at constanttemperature, filament lamp andlight-emitting diode (LED)
Resistor follows ohms law so straight line through origin.
Filament Lamp is non-ohmic as its temperature varies so the
line should go up and then curve so the gradient= 0. LED is non-
ohmic as well, so no current should flow until a certain
threshold voltage, so flat line to indicate no current, then a
upwards line to show current is now flowing.
describe an experiment toobtain the IVcharacteristics of a resistor atconstant
temperature, filament lamp andlight-emittingdiode (LED)
Ammeter, Resistor/Filament Lamp/LED and Potentiometer in
series. Place voltmeter in parallel with the component being
tested. Limit the current flowing by varying the potentiometer
accordingly, taking current and potential difference readings
respectively
describe the uses and benefitsof using light emitting diodes(LEDs).
Advantages or LED over a filament lamp in a torch-Draws lower
current, light lasts longer, LEDs more efficient at converting
electrical energy into light, more robust and a longer working
life.
describe how the resistivities ofmetals and semiconductors areaffected by temperature
Near room temperature, the resistivity of metals typically
increases as temperature is increased, while the resistivity
of semiconductors typically decreases as temperature is
increased.
describe how the resistance ofa pure metal wire and of a Thermistors are temperature sensitive resistors. However,unlike most other resistive devices, the resistance of a
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G482: Electrons, waves and photons
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negative temperaturecoefficient (NTC) thermistor isaffected by temperature
thermistor decreases with increasing temperature.In a pure metal a greater resistance slows the flow ofelectrons so a smaller current flows as temperatureincreases.
describe power as the rate of
energy transfer
power is the rate at whichenergy is transferred, used, or
transformeddescribe how the resistance ofa lightdependent resistor (LDR)depends on the intensity of light
Resistance decreases with increase in light intensityLDR must be shielded or be at some distance from the lamp
when it switches on as the light shining will cause it to switch
the illumination off causing an on/off oscillation
describe and explain the use ofthermistors and light-dependentresistors in potential dividercircuits
Thermistor/LDR can be used to provide an output
voltage, which depends on temperature/light intensity.
describe the advantages ofusing dataloggers to monitorphysical changes
Continuous record for a very long time scale ofobservationsCan record very short timescale signals (at intervals)
Automatic recording/remote sensingData can be fed directly to a computer (for analysis)
describe and distinguishbetween progressivelongitudinal and transversewaves
Longitudinal = oscillations/vibration of particles/medium indirection of travel of the wave e.g. soundTransverse = oscillations/vibration of particles/medium (inthe plane) at right angles to the direction of travel of thewave e.g. surface water, string, electromagnetic
describe differences andsimilarities between differentregions of the electromagneticspectrum
http://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energy8/12/2019 Electrons Waves and Photons Checklist Updated
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G482: Electrons, waves and photons
Text in red is from past papers
Electromagnetic radiation can be described in terms of a
stream ofphotons,which are massless particles each travellingin a wave-like pattern and moving at thespeed of light.Each
photon contains a certain amount (or bundle) of energy, and all
electromagnetic radiation consists of these photons. The only
difference between the various types of electromagnetic
radiation is the amount of energy found in the photons. Radio
waves have photons with low energies, and gamma-rays have
photons with the greatest energies.
describe some of the practicaluses ofelectromagnetic waves
Radio stations. Radio waves are emitted bystars and gases in
space.
Microwaves in space are used byastronomers to learn about
the structure of nearby galaxies.Our skin emits infrared light and In space, IR light maps the
dust between stars.
Visible radiation is emitted by everything from fireflies to light
bulbs to stars ... also by fast-moving particles hitting other
particles. Its the light the human eye can see.
The Sun, Stars and other "hot" objects in space emit UV
radiation.
Hot gases in theUniverse also emit X-rays. They are used in
scanning the bones in the body.
Radioactive materials (some natural and others made by man
in things like nuclear power plants) can emit gamma-rays. Thebiggest gamma-ray generator of all is the Universe! It makes
gamma radiation in all kinds of+\ASA ways.
describe the characteristics anddangers of UV-A, UV-B andUV-C radiations and explain therole of sunscreen
Suncreen filters out (reflects) UV-B protecting skin
UV-A causes tanning or skin ageing, it makes up 99% of UV
light. 400-315nm
UV-B causes damage to cells, skin cancer and sunburn. 315-
200nm
UV-C is filtered out by the atmosphere. 260-100nm
describe experiments thatdemonstrate two source
interference using sound, lightand microwaves
Two speakers playing the same note, hear constructive
(loud) and destructive (quiet) interference.
Light or microwaves pointed towards two slitsconstructive and destructive interference can be
http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photonhttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#speed_of_lighthttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#starhttp://imagine.gsfc.nasa.gov/docs/dict_ad.html#astronomyhttp://imagine.gsfc.nasa.gov/docs/dict_ad.html#dusthttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#universehttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#universehttp://imagine.gsfc.nasa.gov/docs/dict_ad.html#dusthttp://imagine.gsfc.nasa.gov/docs/dict_ad.html#astronomyhttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#starhttp://imagine.gsfc.nasa.gov/docs/dict_qz.html#speed_of_lighthttp://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon8/12/2019 Electrons Waves and Photons Checklist Updated
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G482: Electrons, waves and photons
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describe experiments todemonstrate stationary wavesusing microwaves, stretchedstrings and air columns
Open/closed end air column or string vibrated with a
fixed pointdescribe the particulate nature(photonmodel) of electromagneticradiation
A photon is a quantum/lump/unit/packet/particle of (e-m)energy/light
describe an experiment usingLEDs to estimate the Planckconstant h using the equation
describe and explain thephenomenon of thephotoelectric effect
A photon is absorbed by an electron in a metal surface causing
an electron to be emitted. Energy is conserved. Only photons
with energy above the work function energy will be emitted.
Energy=work function + Max KE of electron. The work function
is the minimum energy required to release an electron from
the surface.
A clean zinc plate is mounted on the cap of a gold leaf
electroscope where the plate is initially charged negatively
Shine a UV light on the plate and watch the gold leaf collapse
as charge leaves the place, indicating the emission of electrons
Work function energy is the minimum energy to release anelectron from the surfaceNumber of electrons emitted also depends on lightintensityEmission is instantaneous
describe the origin of emissionandabsorption line spectra
(Emission) Line spectrum = light emitted from (excitedisolated) atoms produces a line spectrum a series of(sharp/bright/coloured) lines against a dark background.
Absorption spectrum is a series of dark lines (appearsagainst a bright background/within a continuous spectrum)
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G482: Electrons, waves and photons
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The difference between thedirections of conventional
current and electron flow
Current moves from + to(of a battery in circuit) andelectrons move fromto +
Determine
determine the correct fuse for an electricaldevice
The fuse needs to have a current rating bigenough to cover the initial current in thecircuit.
determine the standing wave patterns forstretched string and air columns in closedand open pipes
determine the speed of sound in air frommeasurements on stationary waves in a pipeclosed at one end
Sound waves in the tube are in the form
ofstanding waves,and theamplitude of
vibrations of air is zero at equally spacedintervals along the tube.. The powder is
caught up in the moving air and settles in
little piles at these nodes. The distance
between the piles is one half
wavelength /2of the sound. By measuring
the distance between the piles, the
wavelength of the sound in air can be
found. If the frequency fof the sound is
known, multiplying it by the wavelength
gives the speed of sound cin air:
Explain
explain that electric current is a net flow ofcharged particles
There is a current when charged particles flow
past a point in a circuit. Current is the rate of flow
of charge
explain that electric current in a metal is dueto the movement of electrons, whereas in anelectrolyte the current is due to themovement of ions
Wires are made from metal. The metal contains a
sea of delocalised electrons which move in
random directions. When a cell is connected to
the wire and electrical force is applied to the
electrons making them 'drift'. They still move inrandom directions however they have an overall
http://en.wikipedia.org/wiki/Standing_wavehttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Amplitudehttp://en.wikipedia.org/wiki/Standing_wave8/12/2019 Electrons Waves and Photons Checklist Updated
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G482: Electrons, waves and photons
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velocity or movement, creating a current. This
can happen with ions in an electrolyte too.
explain what is meant by conventionalcurrent and electron flow
The direction of the current is from thepositive terminal to the negative. Howeverelectrons are what flow in metals and are
negatively charged and therefore flow fromnegative to positive
explain how a fuse works as a safety device If the current flows at a higher Amperage, thecollision of electrons causes a high level ofheat, which melts the fuse wire, causing thecircuit to break and the device to beprotected.
explain that all sources of e.m.f. have aninternal resistance
All sources of emf have what is known asINTERNAL RESISTANCE (r) to the flow ofelectric current. The internal resistance of afresh battery is usually small but increaseswith use. Thus the voltage across the
terminals of a battery is less than the emf ofthe battery.
explain how a potential divider circuit can be
used to produce a variable p.d
If you use two fixed resistors in series and
connect the ends to a voltage supply thenthe voltage between both ends and the mid
point where they connect will be in
proportion
their resistor
value. It is
possible to vary
the midpoint
voltage by
changing one of
the resistors.
This can be
done readily
with a variable resistor which than then be
altered to get any value between 0-MaxV
By adjusting the value of R1, the potential
droppedexplain what is meant by reflection,refraction and diffraction of waves such assound and light
Reflection-Bouncing back of wave from a
surface
Refraction-Change in direction of a wave asit crosses and interface between two
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materials where its speed changes
Diffraction-Spreading of a wave when it
passes through a gap or past the edge of
an objectexplain the meaning of the term terminalp.d.; The terminal p.d. of a source is thepotential difference across its terminalsexplain what is meant by plane polarisedwaves and understand the polarisation ofelectromagnetic waves
Transverse waves/vibrations in plane arenormal to the direction of energy propagation.Oscillations are in one direction only
explain that polarisation is a phenomenonassociated with transverse waves only
Electromagnetic waves are transverse waves so
can be polarised whereas sound waves cannot
since they are not transverse.
explain the terms interference, coherence,path difference andphase difference
Interference-When two waves meet at a point
Coherence-Constant phase difference between
the two wavesPath difference-of any point in an interference
pattern of waves is the difference between the
distance travelled by each wave from their source
to that point
Phase difference- difference in velocity of similar
points in two waves expressed as an angle
Coherence = constant phase relationship orare continuous and have the same f/period/
explain the advantages of using multipleslits in an experiment to find the wavelength
of light.
Clearer diffraction pattern which has nofringes, there for more accurate
measurements of different values.explain that the photoelectric effect providesevidence for a particulate nature ofelectromagnetic radiation while phenomenasuch as interference and diffraction provideevidence for a wave nature
There is a threshold frequency which
suggests particle nature, as the wave
theory states that photoelectric emission
should happen as long as the light is bright
enough. However this is not the case.
Diffraction and interference are wave
properties, suggesting that
electromagnetic radiation has wave nature.explain the formation of stationary
(standing) waves using graphical methods
(open end tube and speaker) Using a tube with
one end closed and a loud speaker, the incidentwave is reflected at the end of the pipe and it
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G482: Electrons, waves and photons
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interferes with the incident wave to produce a
resultant wave
(string and oscillator) The incident wave is
reflected at the fixed end of the wire, the
reflected wave interferes with the incident wave
to produce a resultant wave with nodes andantinodes
explain and use Einsteins photoelectricequation hf = + KEmax
Individual photons are absorbed by individual
electrons in the metals surface. These electrons
must absorb sufficient energy to overcome the
work function energy of the metal. The number
of electrons emitted depends on light intensity as
emission is instantaneous.
Infra-red foes not have enough energy to cause
photoelectric emission it is less than the work
functionexplain why the maximum kinetic energy ofthe electrons is independent of intensity andwhy the photoelectric current in a photocellcircuit is proportional to intensity of theincident radiation
Therefore independent of
intensity.
The larger the intensity, the greater the
number of photons emitted, therefore
releasing more electrons generating a
larger current.explain electron diffraction as evidence forthe wave nature of particles like electrons
Electron diffraction refers to the wave
nature of electrons by firingelectrons at a
sample and observing the resulting
interference pattern. This phenomenon iscommonly known as thewave-particle
duality,which states that the behaviour of
a particle of matter (in this case the
incident electron) can be described by a
wave.
Diffraction is a property unique to waves.
If electrons can be diffracted then they
are behaving as wavesexplain that electrons travelling through
polycrystalline graphite will be diffracted bythe atoms and the spacing between theatoms
Graphite, because of its layered structure,
can act as a diffraction grating with very
small slit diameter.
explain that the diffraction of electrons bymatter can be used to determine thearrangement of atoms and the size ofnuclei.
Slow moving electrons, electrons with
wavelengths (E=hf) of the order of
magnitude of the structure (or nuclei) can
be used to probe the properties of atomic
structures.explain how spectral lines are evidence forthe existence of discrete energy levels in
isolated atoms, ie in a gas discharge lamp
Photon produced by electron movingbetween levels
Photon energy equal to energy differencebetween levels
http://en.wikipedia.org/wiki/Electronshttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Wave-particle_dualityhttp://en.wikipedia.org/wiki/Wave-particle_dualityhttp://en.wikipedia.org/wiki/Wave-particle_dualityhttp://en.wikipedia.org/wiki/Wave-particle_dualityhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Electrons8/12/2019 Electrons Waves and Photons Checklist Updated
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G482: Electrons, waves and photons
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Explain how sunscreen protects the humanskin
Filters out/blocks/reflects/absorbs UV (-B)
Explain why electrons can be emitted from aclean metal surface illuminated with brightUV light but never when IR is used, however
intense
Energy of the infra-red photon is less than thework function of the metal surface
Explain what is meant by the de Brogliewavelength of an electron
Electrons are observed to behave aswaves/show wavelike properties where theelectron wavelength depends on itsspeed/momentum
Explain what is meant by a continuousspectrum
All wavelengths/frequencies are present (inthe radiation)
Maths
calculate energy in kW h and the cost of thisenergy when solving problems
solve circuit problems involving series and
parallel circuits with one or more sources ofe.m.f
derive from the definitions of speed,frequency and wavelength, the waveequation v = f
and
then
Wavelength is
the displacement between subsequent
wave peaks therefore draw a simple potential divider circuit
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