Waves and Sound

Waves and Sound

1. Nature of waves

   • We use waves to transfer energy and information
   • Transverse (up and down) oscillate perpendicular to direction of energy transfer
   • Longitudinal (side to side) oscillate parallel to direction of energy transfer

2. Measuring waves

   • Amplitude = height of wave crest/depth of trough from position at rest
   • Frequency = number of wave crests passing a point in 1 second.
   • Wavelength = distance from one wave crest to the next
   • Wave speed = Frequency x Wavelength

3. Reflection and Refraction

   • Plane waves that reflect from straight barrier at same angle to barrier as incident rays = reflection
   • Refraction is change of direction of waves as the cross a boundary, due to change of speed of waves as they cross a boundary.

4. Diffraction

   • It is spreading out of waves when they pass through a gap/round edge of an obstacle.
   • Narrower gap = greater diffraction
   • If radio waves do not diffract enough when they go over hills, reception will be poor.

5. Interference

   • Reinforcement/cancellation of waves when 2 identical sets of waves overlap.
   • When a crest meets a trough, 2 waves cancel each other out
   • When crest meets crest/trough meets trough, reinforce each other
   • Interference is a property of all types of wave.

6. Electromagnetic Spectrum

   • in order: Radio waves, Microwaves, Infrared, Visible, Ultraviolet, X-ray, Gamma rays.
   • Speed (v) = frequency (f) x wavelength (λ)

7. Light + other waves

   • White light contains all colours on spectrum
   • Visible, infrared, microwaves and radiation are all used for communication
   • Microwaves and radio waves can heat internal parts of body. Infrared can burn skin.

8. Communications

   • Radio waves of different frequencies are used for different purposes because their wavelength affects:
     • - how far they travel
       • - how much they spread
     • - how much information they carry
   • Microwaves are used for satellite TV signals
   • Further research is needed to evaluate whether or not mobiles are safe to use.
   • Optical fibres are very thin fibres which are used to transmit signals using light and infrared radiation.

9. U, X, G rays

   • Ultraviolet radiation is shorter in wavelength than light and harms skin and eyes.
   • X-rays are used in hospitals.
   • Gamma rays are used to kill harmful bacteria in food, to sterilise surgical equipment and to kill cancer cells.
   • X-rays and gamma radiation damage living tissue as they pass through.

10. X-rays in hospitals

    • Used to make images and CT scans and to destroy tumours at/near body surface.
    • Can damage living tissue as it passes through
    • Absorbed more by bones and teeth than by soft tissue
    • CT scans distinguish between different types of soft tissue as well as between bone/teeth and soft tissue.

11. Sound

    • Frequency range of normal human ear from about 20 Hz to 20 kHz.
    • Sound waves are vibrations that travel through a substance
    • Cannot travel through a vacuum.
    • Echos are caused by sound waves reflected from smooth, hard surface.

12. Musical Sounds

    • Pitch of note increases if frequency of sound waves increases
    • Loudness of note increases if amplitude of sound waves increases
    • Vibrations created in instrument when played produce sound waves

13. Ultrasound

    • Sound waves of frequency above 20,000 Hz
    • Used in medicine for ultrasound scanning and destroying kidney stones
    • Partly reflected at boundary between 2 different tissue types
    • Ultrasound scan is non-ionising so safer than X-ray