# Physics

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• Physics
• Imaging
• Pixels
• Resolution= Distance / No. of Pixels
• Digital
• 1 bit  - Smallest amount of information (0 or 1)
• 1 byte = 8 bits
• If 'I' is the number of bits
• 2^I is the number of alternatives
• To find number of bits log2(No. of choices needed)
• Uses Binary
• No. of Alternatives = 2
• No. of bits per image
• No. of pixels x No. of bits needed for colour scheme
• No. of bytes = No. of bits / 8
• Coloured Images
• Red + Green
• Yellow
• Red + Blue
• Purple
• Blue + Green
• Syan (Turquoise)
• Red + Blue + Green
• White
• Finding Edges
• Laplace Kernel
• 4
• 0
• -1
• 0
• 0
• 0
• -1
• -1
• -1
• Negative values become 0
• Smoothing
• Median - replace with median of surrounding values
• Mean - Replace with mean of surrounding squares
• Testing Materials
• Young's Modulus
• Stress (Nm-1) = Force (N) / Area (m2)
• YM (Pa) = Stress (Pa) / Strain
• Strain = Extension (m) / Orig. Length (m)
• Types of materials
• Ceramic
• Electrical Insulator
• Plastic
• Often Malleable
• Can be tough
• Can be hard
• Ductile
• Brittle
• Readily cracks on impact or shock
• Thermal Insulator
• Plastic
• Often Malleable
• Can be tough
• Can be hard
• Ductile
• Hard
• Metals
• Tough
• Can withstand large shocks or impacts before breaking
• Sonorous
• Hard
• Does not easily scratch
• Electrical Conductor
• Strong
• Can withstand high stress before yield or fracture
• Thermal conductor
• Malleable
• Can be hammered into sheets
• Ductile
• Can be drawn out into a wire
• Resistance = Resistivity x Length / Area
• Hooke's Law
• Stretching Force (N) =Spring Constant (Nm-1) x Extension (m)
• Only applies up to the elastic limit
• Conductance = Conductivity x Area / Length
• Signalling
• Digital
• 1 bit  - Smallest amount of information (0 or 1)
• 1 byte = 8 bits
• If 'I' is the number of bits
• 2^I is the number of alternatives
• To find number of bits log2(No. of choices needed)
• Uses Binary
• No. of Alternatives = 2
• Sampling Frequency
• At every sampling frequency round to nearest value
• Convert each point sampled on curve to binary
• Draw in bursts digital on/off graph
• Sampling Frequency must be at least 2x highest frequency
• Highest Frequency - W (Hz)=1/T(s)
• Digitizing a Signal
• At every sampling frequency round to nearest value
• Convert each point sampled on curve to binary
• Draw in bursts digital on/off graph
• No. of levels needed
• V-Signal (V) / V-Noise (V)
• No. of bits = log2(No. of levels)
• Velocity = Frequency x Wavelength
• Transmission Rate
• Sampling Frequency x No. of Bits
• 2W log2 ( V-signal / V-noise)
• Sampling Frequency x No. of Bits
• Transmitting Waves
• Digital
• Amplitude Modulated or Frequency Modulated
• Analogue
• Amplitude Modulated
• Wave View
• Amplitude same
• Frequency View
• Frequency on x-axis
• Frequency = 1/T
• Frequency View
• Frequency on x-axis
• Polarisation
• Looking Inside Materials
• Internal Structure
• Crystalline rows of ions in a strict order
• Polycrystalline - A structure made up of many interlocking crystals with grain boundaries.
• Amorphous - Random atoms and molecules in no order
• Bonding in materials
• Metallic - non directional
• Ionic - Non directional
• Covalent - Directional
• Alloys
• Impurities pin dislocatioons so they cannot move through the whole crystal.
• Metals
• Sea of electrons allows positive ions to just slip past each other
• Ductile
• Can be drawn out into a wire
• Sensing
• Types of Resistor
• Resistance increases with voltage as temperature increases
• Resistance calculated by taking spot values
• Ohmic Resistor
• Ratio of V/I is a constant
• Resistance is the constant
• Resistors
• Series
• Rt = R1+R2
• I1=I2=I3
• Vt=V1+V2
• Parallel
• 1/Rt = 1/R1 +1/R2
• Rt = R1R2/R1+R2
• Iseries = Ipara1+ Ipara2
• V=V of battery
• Semiconductors
• LDR, Diode, Thermistor
• In a potential divider circuit
• V of LDR/ V of Ohmic Resistor = R of LDR/R of Ohmic Resistor
• Sensing Circuit
• Sensitivity = Change in Output/Change in Input
• For LDR: Change in PD/Change in distance
• Resolution
• Smallest detectable change in input
• Precision / Sensitivity
• Sensing
• Types of Resistor
• Resistance increases with voltage as temperature increases
• Resistance calculated by taking spot values
• Ohmic Resistor
• Ratio of V/I is a constant
• Resistance is the constant
• Resistors
• Series
• Rt = R1+R2
• I1=I2=I3
• Vt=V1+V2
• Parallel
• 1/Rt = 1/R1 +1/R2
• Rt = R1R2/R1+R2
• Iseries = Ipara1+ Ipara2
• V=V of battery
• Semiconductors
• LDR, Diode, Thermistor
• In a potential divider circuit
• V of LDR/ V of Ohmic Resistor = R of LDR/R of Ohmic Resistor
• Sensing Circuit
• Sensitivity = Change in Output/Change in Input
• For LDR: Change in PD/Change in distance
• Resolution
• Smallest detectable change in input
• Precision / Sensitivity
• Diodes have forward and reverse bias, current can only flow one way
• Potential Divider
• V1/V2 = R1/R2
• EMF and internal resistance
• E=V+Ir
• Improving a circuit
• 2 semiconductor sensors cancels out effect of other factors
• Equations
• I=Q/t
• V=W/Q
• W=ItV
• R=V/I
• R=pL/A
• P=W/t
• P=IV
• E=Pt
• Diodes have forward and reverse bias, current can only flow one way
• Potential Divider
• V1/V2 = R1/R2
• EMF and internal resistance
• E=V+Ir
• Improving a circuit
• 2 semiconductor sensors cancels out effect of other factors
• Equations
• I=Q/t
• V=W/Q
• W=ItV
• R=V/I
• R=pL/A
• P=W/t
• P=IV
• E=Pt

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