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67 Cards in this Set
- Front
- Back
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Frequency |
Number of complete oscillations per second |
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Time Period |
Time taken for one complete oscillation |
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Converging Lens |
Adds curvature to wavefronts, making light from a point converge to a (focal) point
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Focal length |
Distance from the centre of the lens to the focal point |
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Magnification |
Image Size ___________ Object Size |
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Pixel |
A pixel is allocated a binary digit |
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Noise Reduction |
Replaced by taking the median of itself and 8 surrounding pixel values |
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Edge Detection (Laplace Rule) |
Subtract average of pixel values Above, below, left and right |
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Smoothing (Blurring) |
Replacing pixel value with mean of itself and 8 surrounding pixels |
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Bit |
Smallest unit of digital information represented as a 0 or 1 |
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Byte |
8 bit code, which can code for 256 alternatives |
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Resolution |
Smallest Detail that can be distinguished |
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Resolution (in an image) |
Linear measurement ______________________ Number of Pixels |
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How can the resolution of an image be increased? |
Increase the number of pixels on CCD Use a Lens to enlarge image |
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Potential Difference |
J C-1 |
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Current |
C s-1 |
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Charge |
A s |
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Resistance |
V A-1 |
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Conductance |
A V-1 |
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Electromotive Force |
Energy a source can produce for every coulomb of charge flowing round a circuit |
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"Suggest why some p.d. was lost" |
Amount of Energy dissipated per unit charge inside the source due to its internal resistance |
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Power |
J s-1 |
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Ohms Law |
Where Voltage is directly proportional to Current |
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Ohmic Conductor |
Obeys Ohms Law |
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Non-Ohmic Conductor |
Doesn't obey Ohms Law Resistance increases as Current increases Due to heat increasing scattering of atoms |
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Potential Divider |
Two Resistors in series Share source voltage into ratio of resistors Total voltage across resistors = source voltage |
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Sensitivity |
Change in Output ___________________ Change in Input |
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Response Time |
Time taken for sensor to give a reading following a change in its input |
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"State a use for Photocells" |
Generate electricity Light sensor |
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"State a use for Thermistors" |
Temperature Gauge |
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"State a use for Strain Gauges" |
Weighing Scales Force Meter |
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Sampling Frequency |
2 x Max Frequency |
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"State a problem if sampling rate / bits used is too low" |
Forms low Frequency signals Known as "Aliases" |
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Bit Rate = |
Bits per Sample x Samples per second |
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Bandwidth = |
= Highest Frequency - Lowest Frequency = Bit rate = 1 / T (Where T is the time taken to transmit one bit of data in seconds) |
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Noise |
Random fluctuations in pixel / frequency values which degrade the quality |
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"State what is meant by 'Polarisation'" |
Can only happen in Transverse waves Oscillations perpendicular to direction of travel Unpolarised waves oscillate in all planes Polarised waves only oscillate in one plane Vertically polarised waves do not propagate through horizontal polarising filters |
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"State what happens in a Semiconductor when a voltage is applied through it" |
Differ from both Insulators and Metallic conductors Small proportion of atoms are ionised, releasing more free electrons More free electrons means better conductor |
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"How can semiconductors be varied in the manufacturing process?" |
Doping with an element which forms ions easier / harder releasing more / fewer free electrons |
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Conductor |
High density of charge carriers |
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Insulator |
Low density of charge carriers |
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Dense |
Large mass per unit volume |
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Stiff |
Difficult to stretch / extend Indicated by Youngs Modulus |
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Hard |
Difficult to scratch / indent |
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Brittle |
Breaks easily No plastic region Stress concentrated at crack tip Stress cannot be relieved by slip Cracks propagate |
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Tough |
Resistant to propagation of cracks Ability to absorb energy Amount of energy needed to form new surface area |
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Elastic |
Retains it shape after removal of force In metals, bonds stretch and atoms return back to their original position In polymers, long chain of monomers unfold and atoms rotate about their bonds Obeys Hookes Law |
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Plastic |
Doesn't retain its shape after removal of force In metals, planes of atoms dislocate and slip past each other |
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Ductile |
Ability to be drawn into a wire In metals, planes of atoms dislocate and slip past each other |
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Malleable |
Ability to be hammered into shape |
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Breaking Stress |
Amount of force needed to break a material per metre squared |
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Strong |
Requires a large breaking stress |
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Crystalline |
Regular arrangement of atoms in a lattice |
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Polycrystalline |
Atoms in each grain are arranged regularly in rows within a lattice, with different orientations |
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Amorphous |
Random arrangement of atoms No regular structure |
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Metals |
Crystalline / Polycrystalline Strong metallic bonding Sea of delocalised electrons Non directional bonds Planes of atoms can Dislocate Cracks are blunted and Stress can be relieved by Slip Good conductors due to many free electrons |
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Ceramics |
Amorphous Strong Ionic / Covalent Bonding Directional bonds Planes of atoms cannot dislocate Stress cannot be relieved by slip Stress concentrates in cracks and propagates Poor conductors in solid state, Good conductors when molten due to mobility of ions |
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Polymers |
Amorphous / Crystalline A long chain made up of lots of monomers Normally made up of carbon atoms Tangled together Unfold when extended Bonds form between monomers which hold them in place relative to each other |
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Composites |
Combination of two different materials to obtain desired properties from each material |
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"Explain why tensile strength is given as stress measured in Nm-2 rather than as a force measured in N" |
Strength is a property of a material Breaking stress takes cross sectional area into account |
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"Suggest why a filament lamp requires more power than an LED for the same frequency of light" |
Hot filament produces large amount of a infrared Other colours from visible spectrum need filtering out |
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"State where the energy of electrons goes when passing through an LED" |
Into creating and emitting photons of light |
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"Cable is stored tightly wound on a reel, suggest why the current should be low" |
Cooling of cable will be reduced Power dissipated will raise temperature which could become a hazard |
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"State advantages of digital signals" |
Less noise / Can be easily removed Can be reproduced Can be processed by a computer |
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"State disadvantages of digital signals" |
Samples reduces frequency range Introduces low frequency aliases Loss of resolution |
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"Explain what is meant by the term 'digital samples'" |
Samples of the signal taken at discrete intervals and quantised on a digital scale composed of a sequence of binary digits |
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"Explain signals become weaker the further they travel from the hub" |
Signal decreases in amplitude as the wave spreads Radio noise present in environment Noise may degrade signal information |
