Topic 5 - Light and the Electromagnetic Spectrum

• What is total internal reflection?


  ● When light is completely reflected back at a boundary between two mediums

  ● It occurs when light meets a less dense medium at an angle of incidence larger than the critical angle
• What is the critical angle?

  The angle of incidence which causes the angle of reflection to be 90 degrees.
• What determines the colour of visible light waves?

  The wavelength and frequency of the light waves.
• What colour of visible light has the highest frequency?

  violet
• What colour of visible light has the largest wavelength?

  red
• What is meant by the term 'specular eflection'?

  Rays are reflected from a smooth surface in a single direction
• What is meant by the term 'diffuse reflection'?

  Reflection from a rough surface which causes scattering in multiple directions
• How does a red colour filter work?

  ● A red filter absorbs all wavelengths of light other than those in the red range of the spectrum

  ● This means only red light passes through the filter
• What is meant by "opaque"?

  Not see-through
• What governs the colour of an opaque object?

  ● Different objects reflect different wavelengths of light by different amounts

  ● The wavelengths that are most strongly reflected determine the colour
• What happens to the wavelengths of light that aren't reflected by an opaque object?

  Any wavelengths that aren't reflected are absorbed by the object
• What colour does an object appear if all wavelengths are reflected by equal amounts?

  white
• What colour does an object appear if all wavelengths are absorbed?

  black
• What types of waves are electromagnetic waves?

  transverse
• What do electromagnetic waves transfer?

  energy not matter
• What type of spectrum do electromagnetic waves form?

  continuous spectrum
• List the order of the electromagnetic spectrum in order of increasing wavelength

  Gamma, X Ray, UV, Visible, Infrared, Microwaves, Radio
• What is the highest frequency electromagnetic wave?

  gamma waves
• What is the highest energy electromagnetic wave?

  gamma waves
• What properties are shared by all electromagnetic waves?

  ● They are all transverse waves

  ● They all travel at the same speed (3x10⁸ m/s)

  ● They can travel through a vacuum
• What range of frequencies of electromagnetic waves can be detected by the human eye?

  400-700 nanometres
• How do the speeds of EM radiation differ in a vacuum and in air?

  Electromagnetic waves all travel at the same speed in a vacuum and in air.
• What can happen when radiation strikes an object?

  It can be...

  ● transmitted

  ● reflected

  ● absorbed
• What do all bodies (objects) emit and absorb?

  infrared radiation
• What happens to the quantity of infrared radiation emitted by an object as temperature increases?

  The hotter the object, the more infrared radiation it will emit.
• What happens to the type of radiation emitted by an object as temperature increase?

  The hotter the body the shorter the wavelength of radiation release (eg. X rays and gamma rays)
• What is required for a body to be at a constant temperature?

  The body would need to emit radiation at the same rate it absorbs it - it needs to radiate at the same average power that it absorbs.
• Fill in the gaps

  ********

  and********* distribution of any emission depends on temperature.Intensity and wavelength distribution of any emission depends on temperature
• What is meant by intensity?

  The power transferred per unit area; it is a measure of the energy transferred by a wave.
• What will happen if the average power that a object radiates is less than it absorbs?

  the temperature of the object will decrease
• What can be said about the rates of emission and absorption for a body increasing in temperature?

  The body is absorbing radiation faster than it is emitting it.
• Give two factors that affect the temperature of the Earth.

  1. The Earth's rate of absorption and emission of radiation

  2. The amount of reflection of radiation into space
• How does the Earth's atmosphere affect radiation?

  The atmosphere largely absorbs or reflects radiation from the sun, preventing it from reaching Earth. Some radiation, however, is allowed to pass through and warms the earth.
• What happens to the radiation emitted from earth?

  It is absorbed and re-emitted in all directions by greenhouse gases, resulting in the greenhouse effect which warms the earth.
• What type of waves can be produced by oscillations in an electrical circuit?

  radio waves
• How can radio waves create an alternating current in a circuit?

  When radio waves are absorbed, they can induce oscillations in a circuit with the same frequency as the waves themselves.
• Where do gamma rays originate from?

  They originate from changes in the nuclei of atoms.
• What health effects can ultraviolet waves cause?

  ● They can cause the skin to age prematurely

  ● The can increase the risk of developing skin cancer
• What health effects can X-rays and Gamma rays cause?

  ● They are ionising radiation so can cause mutations in genes

  ● They can lead to increased risk of developing various cancers
• What health effects can infrared rays cause?

  Infrared waves can cause burns to skin/tissue.