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73 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are 'Cosmic Rays' ? |
A stream of high-energy particles released from stars like the sun. Originally thought to emanate from terrestrial substances, the ionising effect caused by protons and small nuclei colliding with gas particles was found to be much greater at 5km altitude as opposed to ground level. When these cosmic rays interact with the atmospheric gas particles, they produce a number of different particles, including photons, such as pions, kaons and muons, each of which was discovered with the use of a cloud chamber due to their ionising effect. |
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What is a 'Muon' ? |
Sometimes referred to as the 'heavy electron' - a negatively charged particle with rest mass over 200 times that of the electron. |
'Heavy Electron' |
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What is a 'Pion' ? |
Also known as the 'π Meson' - It is a particle, also created through ionisation of proton cosmic rays. Can come in positive or negative or neutral charge forms. Mass is greater than Muon but less than Proton. (Formed from proton so must be less) |
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What is a 'Kaon' ? |
Also known as 'K meson' - comes in 3 different charges - positive, negative, and neutral. Rest mass larger than π meson but less than proton. |
Think Meson. |
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What are the decay products of a 'K Meson' ?
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A K Meson decays through the weak nuclear force. It's decay products include:
- Pions - Muons + Anti-neutrinos - Anti-muons + Neutrinos. |
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Outline the differences between hadrons and leptons, giving examples to support your answer.
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Hadrons are particles which interact through the strong nuclear force. These include protons, neutrons, mesons, and so forth. In addition, they also decay through the weak nuclear force. Leptons, on the other hand, are not made up of quarks, and in the case of electrons can even be fundamental. Examples of leptons include electrons, muons and neutrinos (with each particle having their corresponding anti-particle). Although leptons do not interact through the strong force, they can interact through the weak nuclear force as well as the electromagnetic force if they are charged, as can hadrons (except neutrinos; uncharged).
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What is the difference between a baryon and a meson?
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A bayron is a hadron particle which indirectly (or directly) decays through the weak nuclear force, into a proton - and is subsequently made up of 3 quark or antiquark combinations. Mesons, on the other hand, are hadrons which subsequently do not include protons in their decay products. Their quark structure is also charactersitic of quark-antiquark pairs, in the case of the neutral pion, this characteristic is precisely why they last so little (short range) - because their quark-antiquark nature means that they annihilate shortly thereafter.
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How would you find the rest energy of the products after a particle accelerator proton high energy collision?
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Because energy is always conserved during a collison; the following principle can be used:
'Total energy before = Total energy after' This can be broken down: 'Rest energy (before) + kinetic energy (before) = Rest energy (after) + Kinetic energy (after).' Therefore, the rest energy of the products after a high-energy proton collision would be: '( Re (B4) + Ke(B4) ) - (Ke(af)) = Re (af)' |
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How can you experimentally prove the existence of varying types of neutrinos?
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When neutrinos formed from muon decay interact with protons and neutrons, they appear to produce muons and anti-muons without electrons. The same can also be said about neutrinos and anti-neutrinos formed from beta decay, when they interact with protons and neutrons, they only produce electrons and positrons.
This can be proven experimentally by allowing the decay products for a muon to hit an absorber. This will absorb the positrons and electrons which form part of the decay products, leaving behind neutrinos and anti-neutrinos from the muon decay. These neutrinos and anti-neutrinos will then hit a 'target' which contains concentrated nuclei. As the neutrinos and anti-neutrinos pass through, most of them will not interact with the nuclei, meaning that the detector on the other end will receive many neutrinos and anti-neutrinos. Some of them, however, will react with the nuclei in the target, and as a result, muons and anti-muons will be produced, and can be picked up by the detector. The absence of any produced positrons or electrons as the neutrinos and anti-neutrinos hit the target proves the idea that there are different types of neutrinos - namely muon & electron neutrinos. |
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How were K Mesons first discovered?
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K Mesons were first discovered in cloud chamber photographs which revealed a 'v-shaped' track from one of the ionising particles. The particles which decayed into pions only were referred to as K Mesons, whereas the particles which decayed into pions in addition to eventually protons were referred to as sigma particles.
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What is a Sigma particle, and why is it strange?
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A Sigma particle is a baryon. It is strange because it contains the 's' or 'anti - s' quark making it strange. It was first discovered as it made a v - shaped track in a cloud chamber, and its decay products included protons, among pions in its decay products.
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When is (and isn't) strangeness conserved?
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Strangeness is always conserved during a strong interaction, and isn't conserved during a weak interaction, as is evident from decays which show that strangeness isn't conserved.
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How would you find experimental evidence for quarks?
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The 3 quark model for baryons was discovered using the stanford linear accelerator. Electrons were made to collide with protons at high-speed. The result showed that the electrons were scattered by 3 different scattering centres inside each proton - which suggested that protons were made up of 3 separate subatomic particles, which we know today as 'quarks' and 'antiquarks'.
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Describe the properties, in terms of charge and strangeness, of quarks.
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Hadrons in particular can be made up of three different types of quarks - known as 'up', 'down' and 'strange' quarks - each with their corresponding antiparticle.
- u - Charge: +2/3 - Strangeness: 0 - d - Charge: -1/3 - Strangeness: 0 - s - Charge: -1/3 - Strangeness: -1 Each anti-quark has opposite properties. |
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What is photoelectricity?
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The act of applying electromagnetic radiation to the surface of a metal. If the conduction electrons receive radiation equal to or higher than a certain threshold frequency, denoted by the work function (thi), the electrons will leave the surface of the metal.
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Why were initial observations about the photoelectricity puzzling for scientists?
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They were puzzling because the current wave-theory explanation for electromagnetic radiation could not explain photoelectricity, especially why such a 'threshold frequency' existed - or why emission always happened instantly.
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Describe some of the observations made by Hertz regarding photoelectricity.
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For emission to take place, the frequency of the incident radiation must be above a value known as the threshold frequency which is dependant on the type of metal.
The rate of electron emission is proportional to the intensity of the incident light and not the frequency itself. Emission occurs instantly, as soon as the incident light is directed at a compatible metal surface, provided the threshold frequency is satisfied. The intensity of light does not affect how soon an electron is emitted, this still happens instantly. To Summarize: - Threshold Frequency. - Intensity = Higher rate. - Emission happens instantly. Intensity does not affect this. |
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What did wave theory incorrectly predict about photoelectricity?
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Wave theory was unable to explain threshold frequency and instant emission of electrons, due to the following incorrect predictions which wave theory predicted:
- Light of any frequency could be used to provoke photoelectric emission - Light of lower intensity would make emission take longer than light of higher intensity |
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Describe the ideas which Einstein used to explain photoelectricity.
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He first assumed that light was made up of wavepackets or photons of energy equal to hf where h = planck's constant, and f = frequency. He went on to explain that when light is incident on a metal surface, an electron absorbs a single photon of energy equal to hf.
He explained that if the absorbed energy exceeds the work function of the metal, denoted by Ø - the minimum energy required for an electron to leave the surface of a metal. This would explain why an increased intensity of light would result in a higher emission rate, and why a threshold frequency exists - as it would need to be above a value to satisfy the work function energy for emission to take place. |
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Describe how electrons can be emitted if the energy provided is equal to the work function, Ø of the metal.
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As the energy, hf, being absorbed by the electron is equal to the work function, there is no leftover energy to provide the electron with kinetic energy to be able to move. In this instance, a potential difference would need to be applied to attract the electrons and cause them to move, allowing them to permanently escape the surface of the metal.
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How can the photoelectric effect be observed?
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This can be done by attaching a zinc plate to a gold leaf electroscope. By negatively charging the electroscope, the gold leaf will rise due to their being the same charge, and pushing against the electroscope.
When the electromagnetic radiation is incident on the zinc plate, emission of electrons should gradually make the electroscope more and more positively charged, the result being that the gold leaf will gradually fall as it is no longer repelling the electroscope. |
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What did Planck suggest about the nature of energy of vibrating atoms?
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Planck suggested that the energy of each vibrating atom is quantised and suggested that only certain levels of energy are allowed, pertaining to a multiple of a basic amount or 'quantum'. He proposed that the energy would be hf, where f is the frequency, and h is a constant.
He imagined that the energy levels be like the rungs of a ladder, and that atoms would emit or absorb radiation when they moved up or down a discrete level - he used this idea to help solve the ultraviolet catastrophe. |
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What is meant by 'quantised energy' and explain its origin.
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The idea of 'quantised' energy came from Planck and Einstein. Plank used the idea of 'lumpy' or discrete energy levels to describe that atoms can only have certain energy levels, composed of a multiple of a basic amount, denoted by hf. Einstein used the idea that light was made up of wavepackets, or photons of energy - this shows overall that energy is quantised - i.e. lumpy and can only occupy certain amounts and cannot spread out evenly.
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What are conduction electrons?
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Electrons that can move about freely within a metal. Their energy depends on the temperature of the metal. It is precisely these electrons that allow for photoelectricity to take place as they absorb energy higher than Ø and escape the surface of the metal.
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What is the work function, Ø, of a metal
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This is the minimum energy required by a conduction electron to be able to escape the surface of a metal.
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What happens when a conduction electron absorbs a photon?
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It gains kinetic energy equal to hf of the photon. If the kinetic energy is greater than the work function, Ø , of the metal, the conduction electron will leave the metal surface. Otherwise, the electron will collide with other electrons and positive ions until the kinetic energy dissipates.
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What is a vacuum photocell?
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A vacuum photocell is a glass tube containing a cathode and an anode. When light is incident on the 'photocathode', electrons are emitted to the anode, and a current is produced.
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Why is photoelectric current proportional to the intensity of light?
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As each electron absorbs one photon, an increased intensity would allow more electrons to absorb a photon in a given space of time, resulting in a higher rate of photoelectric emission and therefore a higher photoelectric current.
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How can the maximum kinetic energy of a photoelectron be measured?
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Using the vacuum photocell. (details not required.)
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How can the work function, Ø, be determined from a graph of E(kmax) against f?
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The work function, Ø, would be the y-intercept.
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What is ionisation?
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An ion is an atom particle which has a different number of protons to electron, giving it an overall charge. Ions are formed from uncharged atoms by adding or removing electrons from the atomic shells. Ionisation can occur if:
- Alpha, beta and gamma radiation passes through a substance. They create ions as they collide with atomic electrons and either displace them, or allow their electrons to join them (such as beta- particles). - Electrons passing through a fluorescent gas tube create ions as they collide with gas particles. |
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How does ionisation occur in a gas tube?
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As a potential difference is applied across a gas tube, electrons are emitted from a metal filament at one end and travel across to the anode at the opposing end. The gas pressure has to be fairly low, so that there are not enough atoms to prevent the electrons from reaching the anode.
As the potential difference is increased, the speed at which the electrons are travelling increases. As electrons emitted from the filament approach the anode, they are at their highest kinetic energy. If sufficient, at this point they will be able to ionise gas atoms by knocking atomic electrons out of their shells. Because of the majority of ionisation occurring near the anode, this increases the current significantly. (More electrons reaching anode than emitted). |
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How can ionisation energy be measured?
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Ionisation energy is simply the work done, W, by a filament-emitted-electron to a gas atom electron in order to knock it out of its shell.
The work done on each electron is equal to the charge of a single electron multiplied by the potential difference across the gas tube. Ionisation energy therefore = eV - where e= charge of electron, and V= pd across gas tube. |
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What is an electron volt?
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A unit of energy equal to the work done by an electron as it passes through a potential difference of one volt.
1.60x10^19C x Voltage. |
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What is excitation?
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Excitation is the process by which electrons can collide with atomic electrons and not ionise them. This occurs at specific energy levels, characteristic of each type of atom, and can only occur if the kinetic energy is less than the ionisation energy. If the kinetic energy is does not satisfy the specific energy level requirements, it will simply be deflected by the atom with no overall loss of kinetic energy.
When a collision between an outer electron and an atomic electron occurs that is sufficient for excitation to take place, the inner shell electron is moved to an outer shell, using up energy equal to the change in energy shells. The result is that the atom is now 'excited'. |
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What are excitation energies and how can they be measured?
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Excitation energies are the energy levels at which atoms can absorb energy and subsequently allow for excitation to take place.
These 'excitation energies' can be measured by increasing the p.d. across a gas-filled tube until the current decreases. The current would decrease as atoms are being excited, due to the incident electrons having reduced their kinetic energy to allow for the excitation to occur. At this point, the p.d. should be measured, and multiplied by 'e', the charge of an electron. (eV). Excitation energies must always be lower than ionisation energies as the electrons do not have sufficient energy to be able to completely displace electrons from their atoms. |
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How is light produced when a p.d. is applied across a gas-filled tube?
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When a p.d. is applied across a gas-filled tube - excitation is made to occur as electrons collide with atoms and move inner shell electrons to outer shells. As this happens, a vacancy is left in one of the inner shell, and is bound to be filled up, making the new electronic configuration temporary. When an electron fills the gap, and moves from a higher energy shell to the lower energy shell with the aforementioned 'vacancy', a photon of energy equal to the difference in shell energy levels is released.
De-excitation may occur directly, or indirectly. An electron may move directly to a lower shell at once, or may move through a series of shells until it reaches the lowest shell. |
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How can photons excite atoms?
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Photons can also cause the excitation of atoms. If an incident photon has energy equal to the difference between a final and initial energy shell, it can be absorbed by the electron, and subsequently cause it to move to the higher energy level, subsequently causing the atom to become 'excited'.
If the incident photon does not have energy equal to the difference between the initial and final energy level shells, then the electron will not absorb the photon. |
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How do fluorescent tubes emit visible light?
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Tubes containing low - pressure mercury vapour is applied with a p.d. across it. As the electrons collide with the gas atoms, they excite. When the mercury atoms de-excite, they emit ultraviolet photons, as well as visible photons and photons of lesser energy. Ultraviolet photons are absorbed by the coating substance of the tube, and its atoms are excited. When the coating atoms de-excite visible photons are released.
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How can you observe the wave-light nature of light?
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Through the use of diffraction.
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How can you observe the particle-like nature of light.
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Through photoelectricity.
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Describe two applications which consider de Broglie wavelengths
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Scanning tunneling microscopes - used to map atoms on a surface. The wave nature of electrons allows them to tunnel between the surface
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Why would the kinetic energy of photoelectrons vary up to a maximum? |
- Electrons orbiting different energy shells might need different amounts of energy to overcome the electrostatic force. - Some electrons may be situated deeper within the metal than just on the surface, and require more kinetic energy to overcome the difference. - They vary up to the maximum of hf-workfunction due to hf being the energy of the photon, and workfunction being the minimum energy required for emission, therefore giving the most kinetic energy left over for the electron. |
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What is electric current defined as? |
The rate of flow of charge, where charge is measured in coulombs. |
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What is a charge carrier, and give two examples of what they could be. |
Charge carriers are the particles which conduct an electrical charge, they are what 'carries' the charge itself. In the case of metals, this would be the conduction electrons. In the case of a salt solution, however, this could be the ions themselves which are free to move and conduct the electrical charge. |
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Define potential difference. |
This is defined as the work done per unit charge of an electron as it passes through a component. The unit of p.d. is the volt, where 1 volt is equal to 1 joule per coulomb. |
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Describe how energy is transferred from electrical energy into thermal energy, as charge passes through a heating component. |
In electrical components which have significant resistance, such as heating components, as charge carriers pass through, they repeatedly collide with the atoms and ions of that substance. As they do so, they transfer their kinetic energy to the atoms through the collisions, and as a result they cause the atoms and ions to vibrate more. As a result of their new vibration and kinetic energy, the resistor becomes hotter. |
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Describe how energy is transferred from electricity to an electric motor. |
The work done by the charge carriers on the motor is transferred by kinetic energy from the motor itself. As the charge carriers pass through the component, they have to travel through a spinning metal wire coil, and oppose the the force on the electrons due to the magnetic field of the motor. SUMMARIZE: - wd transferred as kinetic energy of the motor - charge carriers have to move through spinning metal wire coil against the opposing flow of electrons due to the magnetic field of the motor. |
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Describe how energy is transferred to a loudspeaker electrical appliance. |
The wd on the loudspeaker is transferred as sound energy. Electrons (charge carriers) need to be forced through a similar coil to that of the motor, again, opposing the force on them due to the loudspeaker magnet. As they overcome this and do work, they produce sound energy. |
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What is meant by resistance? And how is it caused? |
Resistance is a measure of difficulty in the passing of current through an electrical component, otherwise known as the opposition to the flow of charged. It is caused by the repeated collision of charge carriers with themselves and the positive ions of the material it is passing through. |
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Explain how you would experimentally determine the resistance of a particular resistor connected in a circuit. |
-Connect an ammeter in series with resistor, so that both have the same amount of current. - Connect a voltmeter in parallel to the resistor in question so that they have the same amount of potential difference. In theory the resistance of the voltmeter should be infinite, but a high resistance should be satisfactory. - Vary the variable resistor in steps to adjust the current and pd as necessary, recording the values as shown on the voltmeter and ammeter respectively for each subsequent 'step' change. - Plot the results on a graph of pd on the y axis, and I on the x axis. Provided that there is a straight line that goes through the origin, determining the gradient of the graph will allow you to obtain the resistance of the resistor. |
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State what is meant by an ohmic conductor. |
A conductor which has a constant resistance; increases in current are proportional to increases in voltage, and vice versa. |
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What is the unit used for resistivity of a material? |
Ohm metre. Ωm. (Not ohm per metre). |
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Explain what is meant by superconductivity. |
A material which has zero resistance / resistivity at and below a critical temperature which depends on the type of material. At such temperatures, the material experiences zero electrical resistance and therefore exhibits superconductivity. |
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What would you expect to happen to the pd across a superconducting material? |
It would reduce to zero, as there would be no resistance and therefore no heating effect. |
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What is meant by a high-temperature superconductor and a low temperature superconductor. |
Any material which exhbits superconductivity at a critical temperature above the boiling point of nitrogen (-196C / 77k) is referred to as a high temperature superconductor, and lower would be a low temperature superconductor. |
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Give two applications for the use of superconductors. |
- High powered electromagnets to generate strong magnetic fields. - Power cables which transfer electrical energy without wastage. |
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What is a diode and what can it be used for? |
A diode only allows current to flow in one direction such that the diode conducts, referred to as the 'forward' direction of the diode. Diodes can be used to protect DC circuits by preventing damage if supply is connected wrong way round, and also used for rectification, to convert AC into DC current. |
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Describe the characteristics of a thermistor and light-dependant resistor. |
As temperature / light intensity increases, the resistance decreases. |
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Describe two ways in which you can investigate the variation of pd and current of a component. |
Using a variable resistance which will vary the current to a minimum, or a potential divider which will vary the current from zero. |
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Give one advantage for using a potential divider instead of a variable resistor. |
Current flowing through a component can be reduced to zero with the use of a potential divider, cannot be done with a variable resistor. |
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Explain what is meant by a positive temperature coefficient. |
A material, such as a metal, which has an increased resistance as temperature increases (They are proportional.) This is because, as the temperature increases, the positive ions of the material vibrate more, making it more difficult for the conduction electrons to pass through, therefore resulting in an increased resistance (And possibly increasing temperature due to more vibration). |
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Explain what is meant by a negative temperature coefficient. |
A material with resistance which is inversely proportional to the temperature applied. As the temperature increases, the resistance decreases. This is because in components like silicon intrinsic semiconductors, and thermistors, as the temperature increases, the amount of conduction electrons increases, therefore reducing the resistance of the componenet. |
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If resistance can change with temperature for any material, suggest why a thermistor should be used regardless. |
This is because the % resistance change per unit change in temperature is much greater in that of a thermistor than something like a metallic wire - as it is much more sensitive, and can give much more precise and accurate temperature sensor readings. |
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Define potential difference. |
The work done per unit charge (coulomb) done from one point to another in a circuit. |
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Describe how heating effect occurs in a heating element. |
Charge carriers repeatedly collide with each other and the positive ions in the metal material. As this happens, there is a net transfer of energy as kinetic energy from the conduction electrons to the positive ions in the material. After such collision, despite the kinetic energy of the electrons being used up in the collision, force due to the potential difference accelerates the electrons across the material until the electron collides with another ion. |
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Describe how the current affects energy / heat transfer. |
The direction of the current does not affect the power supplied, but the magnitude of the current does. |
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Define internal resistance. |
This is the opposition to the flow of charge through the source. This causes some of the energy produced by the source to be dissipated inside the source when charge flows through. |
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Define emf (electromotive force) |
Electrical energy produced per unit charge by the source. |
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Define the pd across the teriminals. |
Emf-pd lost due to internal resistance. This is the electrical energy delivered per unit charge by the source when it forms part of a complete circuit. The difference in energy is caused by dissipated energy due to internal resistance. |
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Describe how you would go about finding the net emf of 2 cells in series, when they are facing the same direction and when they are facing opposite directions. Outline how you would also find the net internal resistance and terminal pd. |
To find the net emf of batteries in series: - If they are facing the same direction, the net emf is the sum of individual emus - If they are facing opposite directions, the net emf is the difference of emfs, with the resultant current direction being in the direction of the cell with the bigger emf. - The total internal resistance is the sum of individual internal resistance as they are connected in series. - To find terminal pd, first find the current by adding the sum of internal resistance + external resistance and dividing emf / total resistance. Emf would then equal emf - Ix(sum of internal resistance). Or, you could also work it out by multiplying external resistance by the current. |
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How would you find the current of 1 out of 4 identical cells in parallel. |
The pd would be the same for each cell, equal to the emf-internal resistance. To find the current going through each cell, imagine that one electron can go through either of the cells, but not all at once. By that standard, it must follow that the current through each cell is a fraction of the original curent, therefore meaning that the current going through one cell out of 4 in parallel would then be I/n, where I=current and n=number of cells in parallel. Use EMF=IR+Ir to find lost pd, terminal pd & cell electromotive force. |
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Describe the necessary conditions required for a silicon diode to be able to conduct electricity. |
Must be placed in the forward direction and have a pd higher than 0.6v. |
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