Waves and the EM spectrum

• Waves transfer energy without transferring matter
• Transverse waves oscillations that are perpendicular to the direction of energy transfer. Eg all EM spectrum
• Longitudinal waves have oscillations that are parallel to the direction of the wave.

  eg

  sound waves

  seismic P waves
• Wavelength is the distance between two peaks or troughs.
• AT AN ANGLE, if light enters a more dense, medium like air, the ray bends towards the normal so the wave is refracted and wave will slow down
• If the wave travels PERPENDICULAR, the wave is reflected
• Specular reflection

  clear image like a mirror

  flat boundary

  angle of I = R

  normals in the same direction
• Diffuse / scattered reflection

  unlike a mirror, we can’t see ourselves at all because the light is reflected in different directions so normals will be different
• when sound waves travel from a less dense to more dense medium their speed increases
• Range of human hearing is 20Hz to 20,000Hz
• Sound waves cannot travel through a vacuum because no particles can vibrate and they rely on particles to transfer energy.
• Ultrasound: <20,000 Hz

  Infrasound: >20 Hz

  humans cannot hear these
• Ultrasound uses: scanners PRODUCE IMAGES of internal organs and foetuses

  👍 it is safer than x-rays because it does not cause mutations, does not increase the risk of cancer
• Infrasound uses:

  investigating the internal structure of our planet

  seismic waves are infrasound waves

  SW: p waves can travel through solids and liquids (faster)

  S waves can travel through solids only (slower)
• Producing a real image

  convex lens (converging)

  drawn like <——> but flipped

  light rays come together so image appears to be

  real

  inverted

  smaller
• producing a virtual image

  concave (diverging)

  drawn like >——< but flipped

  light rays don’t come together where the image appears to be

  virtual

  upright

  smaller
• If the angle of incidence is greater than the critical angle, no refration occurs. All the light is reflected.

  this is TIR
• Radio waves

  uses- communication, broadcasting tv and radio

  waves can be easily reflected to change their direction. produced by oscillations
• Microwaves

  uses: cooking and satellite communications

  when food particles absorb microwaves the internal, thermal energy increases

  easily passed through the atmosphere
• Infrared

  uses: thermal imaging, cooking, optical fibres

  frequencues are absorbed by chemical bomds
• Visible light uses:

  vision, photography
• Ultraviolet uses: sterilisation, UV lamps, fluorescent lights, detecting forged bank notes
• X rays uses:

  airport security scanners and medical x-rays
• Gamma rays uses:

  sterilising, food and medical equipment, detect cancer and it’s treatment
• Harmful effects of excessive exposure to EM radiation

  Microwaves- heats body cells

  Infrared- skin burns

  UV- damages cells and eyes leading to skin cancer

  x-rays and gamma rays: mutation, or damage to cells in the body