Waves

• Waves transfer energy from one place to another without transferring any matter. Waves are either transverse or longitudinal.
• Transverse waves have oscillations perpendicular to the direction of energy transfer Longitudinal waves have oscillations parallel to the direction of energy transfer. Longitudinal waves have compressions and refractions.
• The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.

  The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave.

  The frequency of a wave is the number of waves passing a point each second.
• Label the parts of this wave.

  A) Amplitude

  B) Wavelength

  C) Wavelength

  
• The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.
• All electromagnetic waves:

  Are transverse

  Travel at the same velocity through a vacuum (space or air)
• Fill in the blanks.

  A) Radio

  B) Microwaves

  C) Ultraviolet

  D) Gamma

  
• When waves enter a new medium, the speed changes. If the speed decreases, the wave bends towards the normal line. When waves enter a denser material, they slow down and bend towards the normal line.
• If waves enter a less dense material, they bend towards the normal line. When waves speed up, the bend away from the normal line.
• Refraction takes place due to the differences in velocity of the waves in different substances. Refraction occurs when waves change speed as they pass through different mediums.
• Shorter wave lengths slow down more than longer wavelengths. For example, blue light slows down more than red.
• Explain refraction on a wave front diagram.

  As waves move into a denser medium, the waves slow down. This causes the waves to move closer together and the wavelength to decrease. As the wavelength gets smaller, the waves change direction towards the normal line. After the waves pass through the medium, they speed up, causing them to refract away from the normal line.
• What happens when waves travel into a denser medium?

  Speed: Decrease

  Wavelength: Decrease

  Direction of refraction: Towards normal line
• What happens when waves travel into a less dense material?

  Speed: Increase

  Wavelength: Increase

  Direction of refraction: Away from normal line
• Radio waves can be produced by oscillations in electrical circuits. When radio waves are absorbed they create an alternating current with the same frequency as the radio wave itself, so radio waves can induce oscillations in an electrical circuit.
• Gamma rays originate from changes in the nucleus of an atom.
• Ultraviolet waves can cause skin to age prematurely and increase the risk of skin cancer. X-rays and gamma rays are ionising radiation that can cause the mutation of genes and cancer.
• How do infrared cameras work?

  Different temperatures emit different intensities of infrared radiation. This can be displayed as different colours.
• What are the uses of radio waves? Why are radio waves used for this?

  Tv and radio. Can transmit signals using aerials.

  Have a long wavelength, can travel long distances without losing quality. Can reflect off a layer of charged particles and go around the earth.
• What are the uses of microwaves? Why are microwaves used for this?

  Satellite communication & cooking food.

  Can penetrate through the atmosphere without being reflected/refracted to reach satellites.
• What are the uses of infrared? Why is infrared used for this?

  Cooking food, infrared cameras, electrical heaters, remote controls

  Can transfer thermal energy. Energy is easily absorbed, and can easily be transferred to surroundings, making them heat up.
• What are the uses of visible light? Why is visible light used for this?

  Fibre optics/ communications.

  Has a short wavelength. Is good at reflection and scattering in glass.
• What are the uses of ultraviolet? Why is ultraviolet used for thus?

  Sun tanning, energy efficient lamps.

  Radiates the least heat but most energy. Has a short wavelength to carry more energy, absorbed by the surface of the bulb to be converted to visible light.
• What is X-ray used for? Why is it used for this?

  Medical imaging.

  Has high energy, can penetrate material (body tissue) easily.
• What is gamma used for?

  Sterilising surgical equipment.
• What do transverse and longitudinal waves have in common?

  Travel at the same speed through a vacuum

  Can be reflected/refracted

  Transfer energy
• What happens to X-rays when they enter a bone?

  They are absorbed and do not pass through.
• Describe what happens in the electrical circuit when the car aerial absorbs radio waves.

  An alternating current is induced with the same frequency as the radio waves.
• Explain why refraction occurs as a wave hits shallow water.

  The velocity slows down as a wave hits water so the wave front entering shallow water also slows down because it is entering a denser medium. However, refraction occurs because the front of the wave is entering the deep water at a higher speed which causes the direction of the wave fronts to change.
• State risks of exposure to UV radiation.

  Skin cancer

  Ageing of the skin

  Sunburn

  Eye damage
• Describe how microwaves and visible light are used in communications.

  Microwaves: Signals are transmitted using satellites across the atmosphere

  Visible light: The internet transfers information via visible light in optics.
• Describe how microwaves heat food.

  The microwaves are absorbed by water. The hot water then heats up the rest of the food.