Physics Unit 1 section 1

Physics Unit 1 section 1

1. Waves

   • Frequency
     • Number of vibrations per second
   • Wavelength
     • Length of one whole wave
   • Amplitude
     • Maximum displacement (height)
   • Period
     • Time taken for a whole vibration

2. Electromagnetic spectrum

   • RMIVUXG
   • Microwaves
     • Used in mobile phones
     • Carry signal containing texts
   • Infrared waves
     • Used in heat cameras
     • Carries signal from remote to TV
   • Visible light
     • Used in scientific imaging
     • Image can be recorded electronically

3. Useful equations

   • Frequency = 1/time period
   • Speed = wavelength X frequency

4. Transverse waves

   • Vibrations at right angles to direction
   • All EM waves are transverse

5. Polarisation

   • Waves only oscillate in one direction
   • Polarising filter stops wave going up and down and side to side

6. Converging lenses

   • Change curvature of wavefronts
     • By refraction
   • Adds curvature to waves
   • Slows down light at center of lens for longer than at edges
   • More powerful lens = more curved wavefronts = shorter focal length
   • Power = 1/Fl

7. Lens Equation

   • 1/v = 1/u + 1/f
     • v = lens to image u=lens to object f=focal length
   • Distant source u = 0
   • Magnification = v/u

8. Binary number system

   • Only uses two digits 0 and 1
     • Numbers make up binary digits
     • One binary digit = a bit
     • 8 bits = a byte
   • Used to store data on a computer
     • Saved as a string of bits
     • Number of bits in a string determines how many alternatives it can code for
       • 1 bit = 2 alternatives 1 byte = 256 alternatives
       • Doubles with each bit
       • No. alternatives = 2^No. of bits
       • No.bits = log2^(No. alternatives)

9. Images

   • Array of binary numbers
     • Each pixel = 1 binary number
     • Value gives colour of square
   • Noise
     • Unwanted interfearance
     • Replacing value with mean of 8 around it reduces noise
   • Can be manipulated to alter image

10. Sampling

    • Analogue signals vary continuously
      • Over range of loudness/freq.
    • Electronic signals
      • Will pick up noise
      • Details are lost when reconstructed
      • Easier to reconstruct digital as there are less values
    • Digitising
      • Analogue can be digitised
        • Samples taken at regular intervals
        • Find nearest digital value
        • Quality depends on: resolution and sampling rate
        • Higher resolution = better match
    • Resolution = possible digital values
      • Big number of bits = good resolution
    • Noise
      • Limits amount of bits per sample
    • Sampling rate
      • Minimum = 2 X max frequency

11. Signals

    • Made up of lots of different frequencies
    • Band width: highest frequency - lowest frequency
    • Bits per sec (rate of transmission) = bits per sample X samples per second

12. Digital/Analogue

    • Advantages digital
      • Can be sent/received/reproduced more easily
      • Resistant to noise
      • Used to represent different information
      • Easy to produce using computers
    • Disadvantage digital
      • Can never reproduce analogue completely accurately
      • Some info always lost