Waves~

• Waves only transfer energy, not matter.
• The amplitude of a wave is the maximum displacement of a point a wave from its undisturbed position.
• The wavelength is the distance between the same point on two adjacent waves (eg. between two troughs).
• Frequency is the the number of complete waves passing a certain point per second. It is measured in Hertz (Hz).
• Waves can be either transverse or longitudinal.
• In transverse waves, the oscillations are perpendicular to the direction of energy transfer.
• Examples of transverse waves include:

  • All electromagnetic waves eg. visible light
  • Ripples and waves in water
  • A wave on a string
• In longitudinal waves, the oscillations are parallel to the direction of energy transfer.
• Examples of longitudinal waves include:

  • Sound waves
  • Shock waves eg. some seismic waves
• Wave speed = frequency x wavelength

  v=fλ
• You can use an oscilloscope to measure the speed of sound.
• When waves arrive at a boundary between two different materials, they can be either absorbed, transmitted or reflected.
• In all reflected waves, the angle of incidence = angle of reflection.
• The normal is a line perpendicular to the surface that a wave is being reflected off of.
• Specular reflection is when a wave is reflected in a single direction by a smooth surface eg. a mirror.
• Diffuse reflection is when a wave is reflected by a rough surface and the reflected rays are scattered in many different directions. This is because the normal is different for each ray.
• All electromagnetic waves travel at the same speed through air or a vacuum.
• Waves are refracted when they cross a boundary at an angle. The amount of refraction depends on the density of the material.
• If a wave slows down at a boundary, it will bend towards the normal and its wavelength will decrease.
• If a wave speeds up at a boundary, it will bend away from the normal and its wavelength will increase.
• EM waves are made of oscillating electric and magnetic fields. This means alternating current produces waves that have the same frequency as the ac.
• You can produce radio waves with a transmitter and an ac. When transmitted radio waves reach a receiver, the radio waves are absorbed and generate an ac with the same frequency.
• Radio waves have wavelengths longer than 10cm. If they have a wavelength longer than 1km, they can diffract around bends and hills.
• Radio waves are used for communication.
• Microwaves are used by satellites as they pass easily through Earth's atmosphere.

  They are also used to heat food by transferring energy to the water molecules in the food.
• Infrared radiation is given out by all hot objects and can be used in IR cameras, to cook food, or as electric heaters.
• Fibre optic cables use pulses of visible light to transfer data. Light is not easily absorbed or scatter as it travels along a fibre.
• Fluorescence means an object absorbs UV light and emits visible light. Fluorescent lights generate UV radiation which is absorbed and re-emitted as visible light.
• Overexposure to UV rays can be dangerous.
• X-rays can be used to take images of people's bones. This is because the x-rays pass easily through flesh but not through denser material like bones.
• X-rays and gamma rays are used to treat cancer (radiotherapy).
• Gamma radiation can be used as a medical tracer because the rays can pass out of the body.
• UV radiation damages surface cells which can lead to an increased risk of skin cancer, or even blindness.
• X-rays and gamma rays are types of ionising radiation. This can cause gene mutations or cell destruction, and cancer.
• Lenses form images by refracting light.