Phys Notes DX

Ideas to Implementation | Daniel Xuan

1. ncreased understanding of cathode rays led to the development of television- explain why the apparent inconsistent behaviour of cathode rays caused debate as to whether they were

charged particles or electromagnetic wavesCathode rays exhibited behaviour similar to both waves and particles.

- explain that cathode ray tubes allowed the manipulation of a stream of charged particles Cathode rays are deflected by magnetic and electric fields and allowed scientists to conduct experiments with the rays.

- identify that moving charged particles in a magnetic field experience a force Moving charged particles will force in a magnetic field.Right hand palm rule:

- identify that charged plates produce an electric field Electric field lines show:

- direction of force on a little positive test charge- strength of magnetic field (density and spacing of field lines)

- describe quantitatively the force acting on a charge moving through a magnetic field

F=qvBsinθ

- discuss qualitatively the electric field strength due to a point charges, positive and negative charges and oppositely charged plates

Work done = force x distance = qE x d = qV (V = Ed)

- describe quantitatively the electric field due to oppositely charged plates

E=Vd

units: NC-1 or Vm-1

Note: Electric field is produced by the potential difference set up by the power source


V= change∈potential energycharge

¿work done¿move charge ¿q

¿ force×distanceq

¿ qE×dq

=Ed

- outline Thomson’s experiment to measure the charge/mass ratio of an electron

Method: Electrons are accelerated and collimated from cathode to anode. The cathode ray was deflected with a magnetic field by supplying the Helmholtz coil with a current and the radius of curvature was recorded: Fmagnetic = Fcentripedal

qvB=mv2

rqm

= vBr

In addition to the existing magnetic field, an electric field was applied and both fields were adjusted so that the deflections created by each field was balanced out: Fmagnetic = Felectric

qvB=qE

v=EB

From the size of deflection and the values of E and B, the charge to mass ratio was able to be determined.

Result: He repeated the experiment with different metals and different methods, and found the same result. The q:m ratio was successfully measured and proved that electrons have measurable mass and help end the debate whether cathode rays were a wave or a particle.

Conclusion: The electrons is a:- fundamental- subatomic- negatively charged particle

This contributed to the discovery of electrons and the development of the models of atoms.

- outline the role of: - electrodes in the electron gun

Current heats the cathode causing the cathode to emit a cloud of electrons (improves thermionic emission). The focusing anode creates an electric field which focuses the electrons, its cylindrical shape prevents the electrons from becoming attracted to the walls. The accelerating anode increases the electrons’ velocity as it is more positive.


- the deflection plates or coils Vertical deflection plates deflect cathode rays up and down while horizontal deflection plates deflect the cathode rays left and right.

- the fluorescent screen When exposed to radiation, the phosphor material emits light as it converts the kinetic energy of the electrons into visible light.

in the cathode ray tube of conventional TV displays and oscilloscopesOscilloscopes:

- Electric fields- Display and evaluate signal voltages- Directly measure potential voltage- Respond more rapidly to changing input

signals

TV:- Magnetic fields- Construct complex images- Requires only a change in current to

change deflection- Circular deflection covers larger areas

- perform an investigation and gather first-hand information to observe the occurrence of different striation patterns for different pressures in discharge tubes50.0 mm Hg: violet streamers5.0 mm Hg: faint cathode glow and positive column0.1 mm Hg: cathode glow, Crookes’ dark space, negative glow, Faraday’s dark space and striationsLess than 0.1 mm Hg: glass around anode glows

- perform an investigation to demonstrate and identity properties of cathode rays using discharge tubes: - containing a maltese cross

Wave: Shadow was the cross was seen behind the anodes thus cathode rays travelled in straight lines.

- containing electric plates Wave: Cathode rays were not deflected by electric plates (Hertz) but was proven wrong later (Crookes).

- with a florescent screen Particle: Cathode rays produced fluorescence when it hit the screen thus carrying kinetic energy

- containing a glass wheel Particle: Glass wheel moved as cathode rays possess momentum and mass

- analyse the information gathered to determine the sign of the charge on cathode rays Negatively charged as it was deflected towards positive plate in electric field. Right hand palm can determine the charge of cathode rays in magnetic field

Note:

Wave: Cathode rays were able to pass through gold foil like light through glass however atoms consist of mainly empty space.

Particle: The speed of cathode rays were also less than the speed of light

- solve problem and analyse information using: F=qvBsinθ

F=qE

E=Vd


2. The reconceptualization of the model of light led to an understanding of the photoelectric effect and black body radiation

- describe Hertz’s observation of the effect of a radio wave on a receiver and the photoelectric effect he produced but failed to investigate

Note: Maxwell proposed that:- light is an electromagnetic oscillation (from the acceleration of charged particles)- light is a self-sustaining mutual generation of electric and magnetic fields (perpendicular to each

other and the direction of propagation)which lead to the idea that medium was not required for propagation and the other oscillations of electromagnetic radiation may exist (EM spectrum)Maxwell had also determined the velocity of light to be c

Method: A spark was created between the brass knobs (spark gap) when a high voltage was applied to the transmitter induction coil. The parabolic metal mirrors focus the weak electromagnetic wave (radio wave) to a single point which amplify the intensity of the EMR. The frequency of the receiver is adjusted to match the frequency of the transmitter.

Hertz showed that these waves were able to be reflected using a metal mirror, and refracted as they passed through an asphalt prism. By rotating the receiver loop, the most intense spark was induced only when the receiver loop is parallel to the transmitter loop, proving that radio waves could be polarised.

Result: Sparks were induced at the spark gap of the receiver.

Conclusion: Radio waves could be interfered with, reflected, refracted, diffracted and polarised and that radio waves had properties similar to light.

Photoelectric effect: The experiment was conducted in a dark box so that the tiny sparks could be viewed easier, however Hertz noticed that the sparks were distinctly weaker. He also discovered that the sparks were more vigorous when exposed to UV light (photoelectric effect) using a quartz screen.

- outline qualitatively Hertz’s experiments in measuring the speed of radio waves and how they relate to light wavesMethod: Hertz reflected waves of a zinc metal sheet, the incident and reflected waves interfered and set up standing waves at certain distances. He moved his receiver coil along the wave, sparks were produced at the anti-nodes (areas of constructive interference) and the distance between the anti-nodes is half a wavelength. He then calculated the frequency using the oscillation of the sparks. The speed of electromagnetic waves (c = hλ) was then calculated.

Result: The speed of light was consistent with Maxwell’s calculations.


Conclusion: Radio waves have similar properties to light and that light was indeed what Maxwell’s theory had suggested. He decreased the wavelength and repeated the experiment with different metals.

With Maxwell’s equations, scientists predicted the existence of other forms of EMR which behave similar to light. Hertz’s discovery was the first of its kind to identify another form of EMR and the scientific community to sought out other and develop many uses of EMR.

- identify Planck’s hypothesis that radiation emitted and absorbed by the walls of a black body cavity is quantisedBlack body – ideal physical object which absorbs and/or emits all electromagnetic radiation incident upon it

Characteristics for the distribution of energy for blackbody radiation:

- Intensity varied with wavelength- Temperature of blackbody increases, total

amount of energy emitted increases- Temperature increase, the peak of the

distribution shifts to shorter wavelengths*- Wavelengths of gamma, x-rays and UV are not

emitted at intensity zero**could not be explained using Classical theory

Max Planck’s hypothesis:- Oscillating atoms or molecules can only occupy quantised energy levels – the amount of energy that

an atom can gain or lose is discrete and can only occupy certain energy levels- Quantum of light carries energy proportional to its frequency – energy of light is quantised [E = hf]

h=Planck ' s constant=6.626×10−34 J s

The ultraviolet catastrophe:- In order to emit short wavelengths (UV, X-rays, gamma) atoms will need to undergo a change in

energy that corresponds to the energy of emitted radiation.- Short wavelengths (high frequencies) radiation cannot be emitted because such large energy

changes do not exist in atoms at typical temperatures.- When an electron absorbs enough energy it may be emitted causing ionisation

Existence of peak radiation:- Intensity of radiation (number of quanta) emitted is proportional to the number of atoms

undergoing a change in energy.- The existence of peak radiation is due to certain changes of quantum state of atoms being more

probable at a certain temperature. The more probable changes in energy result in more intense emission of the corresponding wavelength

Classical theory:Frequency: Electrons should be emitted at any frequency, given the intensity is high enough.

Intensity: Electrons will consistently absorb kinetic energy until there’s enough to jump to next energy level.

Kinetic energy: As intensity increases, the kinetic energy increases.

Emission time: At low intensity, electrons would require some time to absorb incident radiation before being emitted from the surface of the metal.

- identify Einstein’s contribution to quantum theory and its relation to black body radiation


Photoelectric effect – phenomenon in which electrons (photoelectrons) are emitted from the surface of the metal when light is shone on the metal

Einstein extended Planck’s concept of quantisation of electromagnetic waves, he postulated that light (EMR) of frequency f can be considered to be a stream of photons which possess discrete energy packets. The collisions between the photon and electron lead to the photoelectric effect.

Photons with energy above the work function of the metal can dispel electrons from the surface as electrons exist in quantised energy levels. The minimum frequency the light must have to cause the photoelectric effect is called the threshold/cut-off frequency whereas the kinetic energy is determined by E = hf. A photon can either transfer enough energy or none at all, if the frequency is below threshold, the energy of the photo is insufficient to eject the electron.

E=hf−∅∅=work functionof metal

When light is shone on the cathode is ejected and travels to the anode, and the flow of charge carriers allows current. If the polarity of the electrodes were reversed, the emitted electrons are repelled (stopping potential – voltage required to prevent electrons from cathode travelling to anode). For current to occur, the kinetic energy of electron overcome the work done by the electric field (KE < qV).

Note: Graphing the photoelectric equation:To covert Joules into electron volts, divide the number of joules by the charge of an electron.The maximum kinetic energy of the electron (eV) is equal to the stopping potential (V).In a maximum kinetic energy (J) vs frequency graph, the gradient is the Planck’s constant, the x-intercept is the threshold frequency and

- explain the particle model of light in terms of photons with particular energy and frequency Light can be reflected, refracted, deflected, interfered and polarised which proves that light is a transverse wave. However, based on quantum theory proposed by Planck, light consists of quantised packets of energy which suggests that light is composed of particles. This phenomenon where by light can behave as both waves and particles is known as the wave-particle duality.

Photon theory of light:- Frequency is related to the amount of energy each photon carries- Intensify is related to the number of electrons

Frequency: If the frequency of the photon is not equal to or greater than the work function, the electrons cannot be ejected regardless of intensity. Threshold frequency is the minimum frequency required to eject an electron it determines the energy possessed by the photon (E – hf).

Intensity: There is a 1:1 photon-electron interaction, the number of electrons emitted is proportional to the intensity of light but only if the light frequency is above threshold frequency.

Maximum kinetic energy: KEmax = Ephoton - ∅

Emission time: Electron are emitted instantaneously.

- identify the relationships between photon energy, frequency, speed of light and wavelength: E=hf

andc=fλ

E=hcλ


- perform an investigation to demonstrate the production and reception of radio waves Method: Radio waves are produced due to oscillating electric charges in an induction coil connected to a 12 V DC power source and a spark was induced about 2 cm between its terminals. As the charges oscillate, the field they produce is distorted and propagates away from the charge at the speed of light. The changing electric field is associated with and perpendicular to the magnetic field component of EMR which is received by the antenna on the radio. The coil is placed 1.5 m away from the radio and the spark was turned on. This is repeated between AM and FM stations and also at 10 m.

Result: The loudness of the static interference was decreased as the distance increase. The FM band also experience less static than the AM band.

Conclusion: Radio waves obey the inverse square law and by placing at a greater distance, the intensity of the wave received was much less, resulting in less loud static interference on the radio. There was much less static interference on the FM band because the radio waves produced by the spark vary significantly and the variations produce the stronger interference on the AM band which decodes amplitude variation as sounds. There is no variations in frequency by the spark so no interference is heard on the FM band.

- identify data sources, gather, process and analyse information and use available evidence to assess Einstein’s contribution to quantum theory and its relation to black body radiation-

- identify data sources, gather, process and present information to summarise the use of the photoelectric effect in:

- solar cells Solar cell converts sunlight into electrical power (photovoltaic effect – movement of charged particles through semiconducting material). The photons are absorbed by the electron-hole pairs in the depletion zone and this provides sufficient energy to free these pairs. The electrons and the positive holes are then influenced by the induced electric field in the depletion layer and electrons accelerate towards the n-type and the hole accelerate to the p-type. This disrupts electrical neutrality which causes potential difference across the crystal and therefore when external is applied, the movement of electrons and holes, the voltage can be harnessed.

- photocells Photocells are electric devices with resistance that alter in presence of light. It consists of a low pressure glass bulb, in which is embedded an anode and a large cathode is coated with photoelectric material. When a circuit is connected, the gap between the cathode and anode prevents current flow despite a supplied voltage. When light shines on the light sensitive cathode, electrons are emitted, as a result of the photoelectric effect, and travels towards the anode. This is used in alarm systems and automatic doors.

- solve problems and analyse information using: E=hf

andc=fλ

Note: Stationary charges produce own electric field, charge moving at a constant velocity produces a magnetic field and accelerating/oscillating charges produce EMR.

- process information to discuss Einstein and Planck’s differing views about whether science research is removed from social and political forcesEinstein was a pacifist while Planck strongly support the German cause.


3. Limitations of past technologies and increased research into the structure of the atom insulted in the invention of transistors

- identify that some electrons in solids are shared between atoms and move freely Rutherford’s model of the atom:

- Dense central core called nucleus consisting of closely packed protons- Orbiting electron undergoes uniform circular motion therefore must be accelerating- According to James Maxwell, accelerating charged particles emit EMR- Electrons lose energy and spiral into nucleus

Bohr’s model:- When atoms absorb energy, electrons may be excited to a new energy level (change in quantum

states)- In returning to a lower, stable energy state, the atom emits radiation corresponding to the change

in quantum satesInsulators: Atoms in the lattice are held strongly by covalent bonds in which electron pairs are shared between atoms and are held tightly. This sharing means electrons are not available to conduct electricity through the lattice.

Conductors: Metal structures consists of cation lattice surrounded by a sea of delocalised electrons. The valence electrons are free to randomly move. Under the influence of an electric field, the random motion of the electrons decreased and begin to have a net motion in the opposite direction of the field, carrying current.

Ionic lattice structure: Valence electrons transfer from metallic atoms to non-metallic to fill up valence shells. The charged ions are held by relatively strong electrostatic attractions with no free moving charges in solid state.

Conductivity depends on the:- number of electrons in the conduction band- charge of an electron- electron mobility

Conductivity = no. of electrons x charge of an electron x electron mobility

- describe the difference between conductors, insulators and semiconductors in terms of band structures and relative electrical resistanceElectrons orbit around the nucleus due to the electrostatic attraction between opposite charges. Electrons in the inner shell are held stronger than those in the outer shells and occupy lower energy levels.

When atoms are closely packed in a lattice structure, electrons in a single atom will interact with neighbouring electrons or even nuclei of other atoms. This results in their highest electron energy levels overlapping in a continuous fashion. These regions are called energy bands.

Energy gap – separation between the outmost filled band and the empty bands and electrons cannot occupy this region and requires a certain amount of energy for electrons to jump from the valence band to the conduction band.


Valence band – made up of the energy levels of the valence electrons of individual atoms and has higher energy levels than the energy bands formed by the electrons in inner shells

Conduction band – when valance electrons gain energy, they might move up into higher energy shells that were previously empty

Only a partial-filled bands contribute to the conductivity as it allows electron-hole pairs to move. When the conduction band is full, there is no space for the electrons to move and thus cannot carry any charge. This also applies to a full valance band.

Conductors have a small energy gap of 0.001 eV. The valance and conduction band overlap with no forbidden energy gap and the relative number of free electrons that can travel between bands is high.

Semiconductors have an energy gap of 1.0 eV. The valence band is almost filled and some electrons can acquire thermal energy to jump into the conduction band. There is a small number of electrons in the conduction band and its number increases as temperature increases this resistivity increases.

Insulators have a large energy gap of 10 eV and has the highest resistance. At room temperature, the conduction band is empty and no electrons is able to jump from the valence band.

- identify the absences of electrons in a nearly full band as holes, and recognise that both electrons and holes help carry currentWhen an electron moves from the valence band to the conduction band, it leaves behind a positively charged, vacant crystal site called a hole. The hole moves in the direction of the electric field and act as positive charge carriers as valence electrons from a nearby bond can move to fill the hole and leaving another one in its original place. The charge carriers of semi-conductors are called electron-hole pairs.

- compare qualitatively the relative number of free electrons that can drift from atom to atom in conductors, semiconductors and insulatorsConductors have the most number of free electrons while insulators have no free electrons in the outer shell.

- identify that the use of germanium in early transistors is related to lack of ability to produce other materials of suitable purityGermanium was used at first because it can be early purified however it was replaced with silicon because silicon semiconductors exhibited consistent behaviour under heat unlike germanium and was also in abundance. Germanium has a smaller energy band gap 0.7 eV compared to silicon’s 1.1 eV.

- describe how ‘doping’ a semiconductor can change its electrical properties Doping refers to the addition of a small number of suitable replacement atoms into intrinsic (pure) semiconductors to improve the conductivity of semiconductors. Doped semiconductors remain electrically neutral.

N-type: Group 15 or pentavalent atom (donor) is added to the silicon and an electron is donated (n because most of the charge carriers are electrons). The pentavalent atom forms bonds with four silicon atoms and one electron is left over. The fifth electron cannot fit in the occupied valence band and has an energy level, (donor level) just below the conduction band and requires very low energy for the electron to jump into the conduction band (~0.05 eV).


P-type: Group 13 or trivalent atom (acceptor) is added to the silicon and an electron is accepted (p because the majority of charge carriers are positively charged holes). The trivalent atoms forms bonds with three silicon and accepts a proton from a silicon and thus a hole is formed. As a result, an empty energy level (acceptor level) is established. It requires very low energy for electrons to jump to the acceptor level from the valence band where holes are formed (~0.05 eV). In presence of an electric field, the holes drift as positive flow.

p-n junction: 2-layer device by sticking a piece of p-type to a piece of n-type semiconductor. Concentration gradient occurs due to the difference in the number of positive and charges, and results in electrons moving from n-type to p-type semiconductors known as diffusion. All mobile charge carriers have been lost and gives rise to the depletion layer/depletion region. The n-type conductors loses electrons and become positively charged and p-type conductors gain electron electrons and becomes negatively charged and thus an electric field is established. The electric field causes electrons to move from n side to p side (diffusion current) and causes holes to move from p side to n side (drift current).

- identify the differences in p and n-type semiconductors in terms of the relative number of negative charge carriers and positive holesThe main charge carriers in n-type are electrons while in p-type semiconductors are holes. Note: The net charge on n-type, p-type semiconductors and p-n junction is neutral.

- describe the differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devicesThermionic devices: A current is run through a heating filament which heats up the cathode so that electrons are ‘boiled’ off and forms a cloud of electrons which travel through a vacuum towards anode.

Transistors: Uses the same principles as p-n junction

Thermionic devices Solid state devicesConducting material (metals)Charge carriers move through vacuumAct as switch or amplifierLargeFragile (glass)Inefficient (produces waste heat)Complex constructionShort-lifeExpensiveDifficult to integrate into circuits

Semiconducting materials (doped silicon)Charge carriers move through materialAct as switch or amplifierMicroscopicRobustEfficientSimple ConstructionLong-lifeCheapEasy to integrate into complex circuits

- perform an investigation to model the behaviour of semiconductors, including the creation of a hole or positive charge on the atom that has lost the electron and the movement of electrons and holes in opposite directions when an electric field is applied across the semiconductorMethod: Place two halves of an egg carton top-bottom (conduction and valence band respectively) at 5 cm difference in height (energy gap). Place a marble (electron) in each egg hole in the lower half. Shake (increase in temperature) the lower half so that a few marbles jump into the upper carton and creates holes in the bottom half. Raise one end of the carton (applied potential difference) and the movement of the marbles represent in flow of charge carriers. Marbles move in the opposite direction of the electric field, while the electron holes ‘move’ in the direction of the field.

- gather, process and present secondary information to discuss how shortcomings in available communication technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistorIn electrical appliances, there is often a need to control the direction of current flow, convert AC into DC, switch current flow on or off, amplify a current or increase the voltage of signals. Prior to the invention of solid state devices, thermionic devices were used.


- identify data sources, gather, process, analyse information and use available evidence to assess the impact of the invention of transistors on society with particular reference to their use in microchips and microprocessorsThe invention of transistors benefitted the society greatly and lead to the invention of integrated circuits and other electric components which could be constructed on a microchip and microprocessor. Information was able to be stored, transferred ad processed faster. Through computers and mobile phones, allowed improved transport and communication methods. This technology is also used in medical equipment and introduced imaging and other surgical machines.

The advancement of technology also meant that the demand for electronic goods increases and resources are allocated into manufacturing, resulting in greater environmental damage. The unemployment rate increased due to the fact that many laborious tasks were computerised and our dependency on technology also increased.


4. Investigation into the electrical properties of particular metals at different temperatures led to the identification of superconductivity and the exploration of possible applications

- outline the methods used by the Braggs to determine crystal structure Diffraction – wave phenomenon where the wavefronts spread out and bend around an obstacle

Diffraction is only obvious when the wavelength is comparable to the spacing of the slits

Thomas Young’s double slit experiment produced light and dark parallel bands. Where there is dark, there is destructive interference and where there is light, there is constructive interference.

For constructive interference to occur, the waves must be in phase by mλ where m is a positive integer (path difference, e.g. path difference is zero at the centre because the distance the waves travel is the same

Diffraction grating – device used to analyse light sources and consists of a large number of equally spaced lines

dsinθ = mλ (m is a positive integer)

Braggs used X-rays (wavelength of 0.1 nm) and shone it on a crystal lattice (atomic spacing of a solid is approximately 0.1 nm). They examined the patterns (Laue pattern) produced by the x-rays after the rays passed through the crystal and hit a photographic screen and used to determine the internal structure of the lattice. The incident X-ray is represented by two parallel beams of X-rays A and B which are initially in phase. However, ray B strikes the second plane of the crystal and travels a further distance of 2dsinθ which was then used to derive Braggs’ equation.

Braggs’ contribution to understanding crystal structure:- Calculation of angles between bright spots allowed the

determination of internal crystal structure- Evidence for the periodic atomic structure- Method to determine crystal structures- Mathematical expression (Bragg’s Law: nλ = 2dsinθ where n is an integer)

- identify that metals possess a crystal lattice structure Through Braggs’ diffraction of X-ray on metal salts, the crystal lattice structure of the metal can be determined.


- describe conduction in metals as a free movement of electrons unimpeded by the lattice Delocalised electrons do not interact with cations except for collisions, where the velocity of the electron is abruptly changed as a result. They maintain thermal equilibrium throughout the lattice and do not interact with each other.

- identify that resistance in metals is increased by the presence of impurities and scattering of electrons by lattice vibrationsThe flow of electrons is inversely related to the resistance of the metals.

Type of metal: The resistivity varies with the type of metal.

Purity: Impurities modify the crystal lattice of the metal and consequently disrupt the flow of electrons.

Temperature: At room temperature, cations oscillate about their equilibrium positions and the lattice oscillation produce phonons (packets of vibration energy). Phonons are exchanged between electrons and cations (electron-phonon interaction) and impedes with the flow of electron. As the temperature increases, electrons and cations have a greater kinetic energy so there are more inelastic collisions and results in the transfer of energy to the lattice thus the resistivity is increased.

- describe the occurrence in superconductors below their critical temperature of a population of electron pairs unaffected by electrical resistanceSuperconductivity – property of zero resistance exhibited at very low absolute temperatures

Critical temperature (Tc) is the temperature below which an object exhibits superconductivity.

Critical temperature of mercury (type I superconductor) is 4.125K

- discuss BCS theory BCS theory states that:

- single electrons do not carry electric current in superconductor- Cooper pairs – paired electrons carry current

Conduction of current in superconductors:1) Electron-phonon interaction: Phonons are exchanged between

electrons and cations during collisions.2) Lattice distortion: At below critical temperatures, electrons move

slowing through the lattice and attracts the surrounding cations to create a more positively charged region.

3) Cooper pair formation: A second electron is then attracted to the charge distortion and the two electrons are indirectly attracted to each other (the two electrons must be travelling in opposite direction). The weak attraction caused by the distortion creates a ‘bound’ state of the electrons and thus a Cooper pair is formed.

Magnetic properties of superconductor:Meissner effect: A superconductor has zero DC resistance and as a result there cannot be any magnetic field inside a superconductor. When the metal becomes superconducting in presence of a weak external magnetic field, the field was expelled from the superconductor. As the external magnetic field increases, the current will increase to prevent external magnetic field penetration.

Superconductors lose their superconductive behaviour above a certain temperature dependant critical magnetic field.

Critical magnetic field of mercury is 0.0411 T.


The lattice distortion establishes an electric force attraction between the electron and positive charge density which is greater than the repulsive forces between electrons. This results in electron pairing and an assisted passage through the lattice with zero energy loss as there is no collision with the lattice. Cooper pairs carry supercurrent relatively unobstructed and facilitated by thermal vibrations.

- discuss the advantage of using superconductors and identify limitations to their use Advantages Disadvantages

Type I - Malleable/ductile- Can withstand physical impact- Easily produced

- Low critical temperature (requires intense cooling)

- Cost to maintain temperatureType II - Liquid nitrogen can cool below critical

temperature- Higher critical temperature

- Brittle- Not ductile- Chemically unstable in some

environments- Difficult to manufacture

Both - Cheaper to run using electricity- Efficient (no resistance = no energy loss)

Superconductors are used in medical equipment (MRIs) for detecting brain disorders. However, they are very expensive to manufacture and to run (cooling).

- process information to identify some of the metals, metal alloys and compounds that have been identified as exhibiting the property of superconductivity and their critical temperaturesType II superconductors are compounds formed from the elements of the transition and actinide series. They are characterised by two critical magnetic fields (Bc1 and Bc2). When the applied field is less than Bc1, the material is superconducting and there is no flux penetration. When the applied field is between B c1 and Bc2, the material is in a mixed state known as the vortex state.

Vortex state: Vortex regions are filaments of normal material that allow flux penetration.

The material still has zero resistance.

The Bc2 of type II superconductors is much larger than the Bc of type I superconductors.

YBa2Cu3O7 has a critical temperature of 93K

- perform an investigation to demonstrate magnetic levitation Method: Cool superconducting material below critical temperature using liquid nitrogen and place a small magnet on top.

Result: The magnet levitates above the superconductor.

Conclusion: Repulsive force between magnet and superconductor is equal to the weight force of the magnet.

- analyse information to explain why a magnet is able to hover above a superconducting material that has reached the temperature at which it is superconducting Cooper pairs form when the temperature of the superconductor is reduced to below critical temperature, and allows the electron pairs to travel through lattice unimpeded. In presence of an external magnetic fields, the electron pairs begin to create current loops that produce a magnetic field to prevent flux penetration of the rare earth magnet into the superconductor (Meissner effect). As the type II superconductor experiences a change in flux, surface currents (no resistance) are induced to produce a strong magnetic field equal in magnitude and opposite direction to the field of the magnet (Lenz’s Law). The repulsive force between the magnet and superconductor counteract the weight force of the magnet.


- gather and process information to describe how superconductors and the effects of magnetic fields have been applied to develop a maglev trainMaglev trains levitate from the guide way (corresponding to the rail tracks of conventional railways) by using electromagnetic forces between superconducting magnets on board the train and coils on the ground. Since there is no contact, there is no friction between the surfaces and allows higher speed.

1) Magnetic levitation – A superconductor is place at the bottom of the train and when the train passes, an electric current is induced within the coils under the rails, which then act as electromagnets temporarily. As a result, there are forces which pushes and pulls the superconducting magnet upward simultaneously.

2) Lateral guidance – When the train passes, an electric current is induced in the coils and displaces the train laterally, There is a repulsion and attractive force on both sides of the train which allows it to position the train in the centre of the track.

3) Propulsion – Propulsion coils located on the sideways are energised by a three-phase alternating current creating a shifting magnetic field which repels and attracts the train forward.

- process information to discuss possible applications of superconductivity and the effects of those applications on computers, generators and motors and transmission of electricity through power gridsComputers: Integrated circuits can process large amount of data and only takes a small amount of space. The speed and further miniaturisation of computer chip are limited by the generation of heat. Supercomputers are able to perform extremely complex operations at much enhanced speed. However, it requires coolants to run.

Motors and generators: The low resistance means that with any given voltage, the net current flow in motors will be greater. Since there is no loss of energy, motors are more efficient and smaller as it does not require an iron core.

Power transmission and transformers: There is no energy loss during power transmission and can carry three times more current. This would reduce cost of power and satisfy the growing demand for electricity. However, due to their brittle nature and the requirement to cool superconductors below critical temperatures, superconductors are not used as transmission lines.

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