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75 Cards in this Set
- Front
- Back
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Define the coulomb |
The SI unit of electrical charge. 1 coulomb of electrical charge is the amount of charge transferred by a current of 1 amp per second |
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Define potential difference |
Energy transfer per unit charge from electrical energy to other forms |
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Define the Volt |
1 Volt is equal to 1 Joule per coulomb |
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Define electromotive force of a source such as a cell or a power supply |
The energy gained per unit of charge by charges passing through a supply. Measured in V or JC^-1 |
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Define resistance |
Resistance = Potential difference / current |
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Define the ohm |
1 Ohm is the resistance of a component when a potential difference of 1 Volt is produced per ampere of current. |
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Define resistivity of a material |
Resistivity is equal to the product of the resistance and cross sectional area divided by the length. P=RA/l |
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Define the kilowatt-hour as a unit of energy |
A unit of energy equal to 3.6 MJ or 1kW for 1 hour |
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Define the term displacement |
Distance from the mean position expressed as a vector or any distance moved from equilibrium of a point/ particle (on a wave) |
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Define the term amplitude |
the maximum possible displacement (caused by wave motion) |
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Define wavelength |
Distance between neighbouring identical points |
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Define period |
Time taking for one complete oscillation of a particle |
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Define the term phase difference |
the fraction of a cycle between the oscillation of two particles
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Define the term Frequency |
Number of waves passing a point per unit time |
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Define speed |
Distance travelled by a wave per unit time. |
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Define the term nodes and antinodes |
Nodes - when the amplitude is always zero Antinodes - When the amplitude is always at its maximum possible value |
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Define the terms fundamental mode of vibration and harmonics |
Fundamental mode - simplest pattern of movement and has the lowest possible frequency band and the longest wavelength Harmonics - different modes of vibration of a wave with increasing frequency and decreasing wavelength |
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Define the electronvolt |
Energy acquired by an electron accelerated through a p.d of 1V. 1 eV is gained or lost when an electron moves through a potential difference of 1V |
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Define the terms work function and threshold frequency |
Work function - the minimum energy required to release an electron from the surface of a material. Threshold frequency - frequency of a photon that will just emit an electron from a substance without any kinetic energy. |
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Define the term intensity |
the incident energy per unit area per unit time |
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State what is meant by the term mean drift velocity of charge carriers |
The average distance travelled by the charge carriers along the wire per second. |
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State Ohm's law |
For a metallic conductor at a constant temperature, the current in the conductor is directly proportional to the potential difference across it |
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State Kirchoff's second law |
Sum of EMF is equal to the sum of P.D's in a closed loop. Energy is conserved. |
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State the typical values for the wavelengths of different regions of the electromagnetic spectrum from radio waves to ultraviolet rays. |
Visible light: 700-400 nm (5*10^-7) UV -A 400-315nmm UV -B 315-260nm UV-C 260-100nm |
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What speed do electromagnetic waves travel at in a vacuum. |
All travel in same speed of light : 3*10^8 m/s |
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How is light affected when being reflected? |
It is partially polarised. |
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What is the principle of superposition of waves? |
When two or more waves meet at a point and interfere, the sum of their individual displacements is equal to the resultant displacement. |
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What is mean by constructive and destructive interference? |
Interference is when two waves superpose at a pint and there is a change in overall intensity/displacement. |
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What is a photon considered to be in the electromagnetic radiation? |
It is a photon of energy.
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What is conserved when a photon interacts with an electron? |
Energy is conserved. |
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What are the charge carriers in an electrolyte and through wires? |
In electrolytes they are ions. In wires they are electrons. |
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What is Malus' Law? |
The intensity of light transmitted through a plarising filter is equal to I*Cos^2@ where I is the original current and @ is the angle between polarisers. |
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Describe the relationships between Intensity and power and Intensity and amplitude |
Intensity = power/cross sectional area Intensity is inversely proportional to the amplitude^2 |
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What is the separation between adjacent nodes or anti nodes? |
half a wavelength. |
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What is the equation of eV in terms of mass and velocity? |
eV = 05 * mass * Velocity^2 |
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What is Kirchhoff's First Law? |
Total current entering a junction is equal to the total sum leaving it. Charge is conserved |
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Describe the difference between conductors, semiconductors and insulators in terms of number density n. |
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. Insulators have very few/no charge carriers therefore don't let any current flow. |
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Describe how a voltmeter and an ammeter may be used to measure p.d and current in a circuit. |
Ammeter must be put in series to measure current. Voltmeter must be put in parallel. |
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Describe the IV characteristics of a resistor. |
Current is directly proportional to potential difference so it has a straight line through the origin. It obeys Ohm's law. |
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Describe the IV characteristics of filament lamp. |
It's non ohmic as it's temperature varies so the line should go up and then curve so the gradient is 0. |
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Describe the IV characteristics of LED. |
Non ohmic so no current should flow until a certain threshold voltage - straight flat line - then line goes upwards beyond threshold voltage showing that the current is flowing. |
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Describe an experiment to obtain the IV characteristics. |
place the ammeter/resistor/filament lamp/LED and pententiometer 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. |
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Describe the uses and benefits of using LED's |
Draws lower current and lasts longer than filament lamp. They're more efficient at converting electrical energy into light, more robust and a longer working life. |
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Describe how the resistivity of metals and semiconductors are affected by temperature. |
Resistivity of metals increases as temperature is increased, while the resistivity of semiconductors decreases as temperature is increased. |
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Describe how the resistance of a pure metal wire and of a negative temperature coefficient thermistor is affected by temperature. |
Thermistors are temperature sensitive resistors. Resistance of a thermistor decreases with increasing temperature. In a pure metal a greater resistance slows the flow of electron so a smaller current flows as temperature increases. |
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Describe power as the rate of energy transfer |
Power is the rate at which energy is transferred, used, or transformed. |
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Describe how the resistance of a LDR depends on the intensity of light. |
Resistance decreases with increase in light intensity. LDR must be shielded or be at some distance from the lamp when in switches on as the light shining will cause it to switch illumination off causing an on/off oscillation. |
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Describe the advantages of using dataloggers to monitor physical changes. |
continuous record for a very long time scale of observations. Can record very short timescale signals. Automatic recording sensing Data can be fed directly to a computer |
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Describe the difference between longitudinal and transverse waves. |
Longitudinal - oscillations are in the same direction as the travel of the wave. eg sound. Transverse - oscillations at right angles to the direction of travel of the wave. eg electromagnetic |
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Describe the differences and similarities between different regions of the electromagnetic spectrum. |
Electromagnetic radiation can be described as a stream of photons. Each photon contains a certain amount of energy. The difference between the various types of EM radiations the amount of energy found in the photons. Radio waves have photons with low energies and gamma rays have photons with the greatest energies. |
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Describe the practical uses of EM Waves |
Radio waves - radio stations Microwaves - used by astronomers to learn about the structure of galaxies. IR - map out dust between stars. Detecting human bodies - police cameras. UV - tanning , baby scan, medicine. Xray - medicine imaging Gamma - Chemo |
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Describe characteristics and dangers of UV-A, UV-B and UV-C radiations and explain the role of suscreen. |
Sunscreen filters out / reflects UV-B protecting skin. UV-A causes tanning or skin ageing. UV-B causes damage to cells, skin cancer & burns UV-C filtered out by atmosphere |
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Describe an experiment that shows two source interference using sound, light and microwaves.
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Two speakers playing the same note, hear constructive and destructive interference. Light or microwaves pointed towards two slits constructive and destructive interference can be observed. |
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Describe constructive and destructive interference in terms of path difference and phase difference. |
If path difference between two light waves is (m+1/2) wavelengths, then the interference between the will be destructive. For constructive interference, path difference between two waves is m wavelengths. |
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Describe Young's Double Slit experiment and explain how it is a classical confirmation of wave like nature of light. |
Monochromatic (one wavelength present) source is sent through 2 slits which diffracts the source. Diffraction shows wave like nature. |
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Describe the similarities and differences between progressive and stationary waves. |
Progressive - a wave which transfers energy, it transfers shape from one place to another.
Stationary - a wave which traps/ stores energy, the shape does not move along. Stationary wave = incident wave is reflected at the end of the pipe. Reflected wave interferes/superposes with the incident wave to produce nodes and antinodes. |
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Describe the particulate nature (photon model) of EM radiation. |
A photon is a quantum/lump/unit of EM energy. |
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Describe an experiment using LED's to estimate the Planck constant h using the equation. |
Adjust potential divider to zero voltage. Connect the lead to one LED Increase voltage until LED just lights/strikes Repeat several times and average to find Vmin Repeat for each LED Shield LED inside opaque tube to judge strike more accurately. |
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Describe + explain the photoelectric 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. The work function energy is the minimum amount of energy required to release an electron from the surface. Number of electrons emitted also depends on light intensity. Emissions are instantaneous. |
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Describe an experiment to show the photoelectric effect. |
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. |
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State the difference between the direction of conventional current and electron flow. |
Conventional current moves from + to - of a battery in circuit. Electron move from - to + |
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Describe and explain how the movement in metals produces a current. |
When a cell is connected to the wire and electrical force is applied to the electrons, the electrons drift. They move in random directions however they have an overall velocity or movement creating a current. |
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What do all sources of EMF have? |
They all have internal resistance. This can be very small in fresh batteries but usually increases with use. |
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Explain what is meant by reflection, refraction and diffraction of waves. |
Reflection - Bouncing back of wave from a surface Refraction - change in direction of a wave as it crosses and interface between two materials where its speed changes. Diffraction - spreading of a wave when it passes through a gap or past the edge of an object. |
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Explain the meaning of the term terminal p.d |
The terminal p.d of a source is the potential difference across its terminals. |
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Explain what is meant by polarised waves. |
Transverse waves/vibrations in plane are normal to the direction of propagation. Oscillations are in one direction only. |
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Why can sound waves not be polarised but EM waves can? |
EM waves are transverse waves so can be polarised whereas sound waves are not transverse. |
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Explain what is meant by the terms interference, coherence, path difference and phase difference. |
Interference - when two waves meet at a point. Coherence - constant phase difference between the two waves Path difference - 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. |
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Explain advantages of using multiple slits in an experiment to find the wavelength of light. |
There is a greater angle between maxima (bright fringes) and elsewhere zero intensity so easy to measure. |
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Explain how the photoelectric effect provides evidence for a particulate nature of EM radiation. |
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. |
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Explain the formation of stationary waves using graphical methods. |
Using end tube (one end closed) and speaker - the incident wave is reflected at the end of the pipe and it interferes with the incident wave to produce a resultant wave. Using string and oscillator- 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 and antinodes. |
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Explain Einstein's Photoelectric Equation. |
Individual photons are absorbed by individual electrons in the metal's surface. These electrons must absorb sufficient energy to overcome work function energy of the metal. The number of electrons emitted depends on light intensity as emission is instantaneous. |
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Explain why the maximum kinetic energy of the electron is independent of the intensity. |
The larger the intensity the greater the number of photons emitted. Therefore intensity is independent. |
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how does electron travelling through graphite result in diffraction. |
The layered structure of graphite act as diffraction grating with very small slit diameter. |
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Explain why electrons can be emitted from a clean metal surface with UV light but never with IR light. |
Energy of infra - red photon is less than the work function energy of the metal surface. |
