Electrons Waves and Photons Checklist Updated

8/12/2019 Electrons Waves and Photons Checklist Updated

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G482: Electrons, waves and photons

Text in red is from past papers

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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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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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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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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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/Energy


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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#photon


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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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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_wave


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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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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/Electrons


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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

Electrons Waves and Photons Checklist Updated

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