Physics Unit 1 section 1

Waves
1. Frequency
  1. Number of vibrations per second
2. Wavelength
  1. Length of one whole wave
3. Amplitude
  1. Maximum displacement (height)
4. Period
  1. Time taken for a whole vibration
Electromagnetic spectrum
1. RMIVUXG
2. Microwaves
  1. Used in mobile phones
  2. Carry signal containing texts
3. Infrared waves
  1. Used in heat cameras
  2. Carries signal from remote to TV
4. Visible light
  1. Used in scientific imaging
  2. Image can be recorded electronically
Useful equations
1. Frequency = 1/time period
2. Speed = wavelength X frequency
Transverse waves
1. Vibrations at right angles to direction
2. All EM waves are transverse
Polarisation
1. Waves only oscillate in one direction
2. Polarising filter stops wave going up and down and side to side
Converging lenses
1. Change curvature of wavefronts
  1. By refraction
2. Adds curvature to waves
3. Slows down light at center of lens for longer than at edges
4. More powerful lens = more curved wavefronts = shorter focal length
5. Power = 1/Fl
Lens Equation
1. 1/v = 1/u + 1/f
  1. v = lens to image u=lens to object f=focal length
2. Distant source u = 0
3. Magnification = v/u
Binary number system
1. Only uses two digits 0 and 1
  1. Numbers make up binary digits
  2. One binary digit = a bit
  3. 8 bits = a byte
2. Used to store data on a computer
  1. Saved as a string of bits
  2. Number of bits in a string determines how many alternatives it can code for
    1. 1 bit = 2 alternatives 1 byte = 256 alternatives
    2. Doubles with each bit
    3. No. alternatives = 2^No. of bits
    4. No.bits = log2^(No. alternatives)
Images
1. Array of binary numbers
  1. Each pixel = 1 binary number
  2. Value gives colour of square
2. Noise
  1. Unwanted interfearance
  2. Replacing value with mean of 8 around it reduces noise
3. Can be manipulated to alter image
Sampling
1. Analogue signals vary continuously
  1. Over range of loudness/freq.
2. Electronic signals
  1. Will pick up noise
  2. Details are lost when reconstructed
  3. Easier to reconstruct digital as there are less values
3. Digitising
  1. Analogue can be digitised
    1. Samples taken at regular intervals
    2. Find nearest digital value
    3. Quality depends on: resolution and sampling rate
    4. Higher resolution = better match
4. Resolution = possible digital values
  1. Big number of bits = good resolution
5. Noise
  1. Limits amount of bits per sample
6. Sampling rate
  1. Minimum = 2 X max frequency
Signals
1. Made up of lots of different frequencies
2. Band width: highest frequency - lowest frequency
3. Bits per sec (rate of transmission) = bits per sample X samples per second
Digital/Analogue
1. Advantages digital
  1. Can be sent/received/reproduced more easily
  2. Resistant to noise
  3. Used to represent different information
  4. Easy to produce using computers
2. Disadvantage digital
  1. Can never reproduce analogue completely accurately
  2. Some info always lost

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Physics Unit 1 section 1

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