Waves and the Electromagnetic Spectrum

• Transverse waves

  Examples: Water waves, seismic S wave, all electromagnetic waves (EM) such as visible light, UV, X-rays

  Direction of oscillation in relation to wave direction: Perpendicular to the wave direction.

  Energy transferred? Yes

  Information transferred? Yes

  Matter transferred? No. Particles oscillate up and down as wave passes but they then return to their original position (the equilibrium)
• Longitudinal waves

  Examples: Sound, shock wave, seismic P wave

  Direction of oscillation in relation to wave direction: Parallel to the wave direction.

  Energy and information transferred? Yes

  Matter transferred? No

  Particles oscillate forward and back as wave passes but they then return to their original position (the equilibrium)
• Amplitude

  The maximum displacement of the oscillation from the equilibrium point. In sound this relates to how loud the sound is and in water waves this relates to the height of the wave crest above the equilibrium point.
• Wavelength

  The distance between two consecutive crests on a transverse wave or the distance between two consecutive compressions in a longitudinal wave.
• Time period

  The time for one wave to pass
• Frequency

  The number of waves that pass per unit time
• Frequency = number of waves/time for waves to pass
• wave speed = frequency * wavelength

  wave speed is measured in meters per second (m/s)

  frequency is measured in Hertz (Hz)

  wavelength is measured in meters (m)
• T = 1/frequency
• EM spectrum

  Frequency from low to high, wavelength from long to short

  Radio waves, microwaves, infrared, visible light, ultra-violet, x-rays, gamma rays
• Visible light (ascending frequency, descending wavelength)

  red, orange, yellow, green, blue, indigo, violet
• Radio waves

  Uses:

  • Broadcasting, communications and satellite transmissions
  • They have long wavelengths and are reflected by the ionosphere
• Infrared

  Uses

  • Cooking, thermal imaging, short range communications and television remote controls
  • Their wavelengths make them able to penetrate short distances and deposit enough energy to heat objects

  Danger from excessive exposure

  • Skin burns
• Visible light

  Uses

  • Sight, photography, illumination and optical fibres.
  • We see wavelengths of visible light.
  • Visible light can travel through glass wires (optical fibres) by total internal reflection.

  Danger from excessive exposure:

  • Damage to the retina at the back of the eye
• Ultraviolet

  Uses

  • Security marking and fluorescent lamps
  • When some substances absorb UV, they will emit visible light (called fluorescents)

  Danger from excessive exposure

  • Damage to surface cells and eyes, leading to skin cancer and blindness
  • Sun cream and sunglasses help prevent excessive exposure
• X-rays

  Uses

  • Observing the internal structure of objects, including airport security scanners and medical X-rays
  • Because of their short wavelength, X-rays easily penetrate soft materials but are absorbed by more dense materials

  Danger from excessive exposure

  • X-rays are ionising, they can cause cell mutation leading to cancer
  • Protective (lead) shielding helps prevent exposure
• Gamma rays

  Uses

  • Sterilising food and medical equipment
  • Gamma's high energy can kill cells including pathogens

  Danger from excessive exposure

  • Gamma-rays are ionising, they can cause cell mutation leading to cancer
  • Protective (lead) shielding helps prevent excessive exposure
• Which part of the electromagnetic spectrum can be detected by our eyes?

  Visible light
• Which part of the EM spectrum can be detected by our skin?

  Infrared
• Give three examples of a wave transferring energy.

  Energy reaching Earth from the Sun

  Microwaves cooking food

  Infrared from a heater warming a room
• Give three examples of a wave being used to transfer information

  Light allowing us to see things

  Sound waves transferring speech

  Radio waves transferring radio/TV programmes
• Give 4 uses of ultraviolet radiation

  Showing security markings, fluorescent lamps, detecting forged bank notes, sterilising water
• Give 6 uses of gamma rays

  Sterilising food, sterilising medical equipment, detecting cancer, treating cancer, killing bacteria, killing microorganisms
• State one danger of infrared radiation and describe one way to keep yourself safe from the danger you have stated.

  Skin burns.

  Not getting too close to sources of infrared
• Give two similarities and one difference between transverse and longitudinal seismic waves.

  Similarities: Both transfer energy, both involve the oscillations/vibrations of particles

  Difference: In transverse waves the particles vibrate at right angles to the direction of travel, in longitudinal waves they vibrate in the same direction as the direction of travel
• Four waves pass a mark on a tank each second. What is the period of the waves?

  0.25 s
• A sound wave has a frequency of 500 Hz and a wavelength of 0.7m. What is the speed?

  350 m/s