♡ Topic 5_Light and the electromagnetic spectrum ♡

• Total internal reflection:

  • Light is completely reflected back at a boundary between two mediums
  • Occurs when light meets a less dense medium at an angle of incidence larger than the critical angle
• Critical angle:

  • The angle of incidence which causes the angle of reflection to be 90 degrees
• Colour of visible light waves is determined by the wavelength and frequency of the light waves
• Colour of visible light with the highest frequency is blue
• Colour of visible light with the largest wavelength is red
• Specular reflection:

  • Rays are reflected from a smooth surface in a single direction
• Diffuse reflection:

  • Reflection from a rough surface which causes scattering
• Red colour filter works by:

  • Absorbing all wavelengths of light other than those in the red range of the spectrum
  • Allowing only red light to pass through the filter
• Opaque means not see-through
• Colour of an opaque object is governed by:

  • Different objects reflect different wavelengths of light by different amounts
  • The wavelengths that are most strongly reflected determine the colour
• Wavelengths of light that aren't reflected by an opaque object are absorbed by the object
• Object appears white if all wavelengths are reflected by equal amounts
• Object appears black if all wavelengths are absorbed
• All bodies (objects) emit and absorb infrared radiation
• The hotter the object, the more infrared radiation it will emit
• The hotter the body, the shorter the wavelength of radiation released (e.g., X rays and gamma rays)
• For a body to be at a constant temperature, it needs to emit radiation at the same rate it absorbs it - it needs to radiate at the same average power that it absorbs
• Intensity and wavelength distribution of any emission depends on temperature
• Intensity is the power transferred per unit area; it is a measure of the energy transferred by a wave
• If the average power that an object radiates is less than it absorbs, the temperature of the object will decrease
• For a body increasing in temperature, it is absorbing radiation faster than it is emitting it
• Factors that affect the temperature of the Earth:

  • The Earth’s rate of absorption and emission of radiation
  • The amount of reflection of radiation into space
• The Earth’s 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
• Radiation emitted from the Earth is absorbed and re-emitted in all directions by greenhouse gases, resulting in the greenhouse effect which warms the earth
• Electromagnetic waves are transverse waves
• Electromagnetic waves transfer energy (not matter)
• Electromagnetic waves form a continuous spectrum
• Order of the electromagnetic spectrum in increasing wavelength:

  • Gamma
  • X Ray
  • UV
  • Visible
  • Infrared
  • Microwaves
  • Radio
• Highest frequency electromagnetic wave: Gamma waves
• Highest energy electromagnetic wave: Gamma waves
• Properties shared by all electromagnetic waves:

  • They are all transverse waves
  • They all travel at the same speed (3x10^8 m/s)
  • They can travel through a vacuum
• Range of frequencies of electromagnetic waves detected by the human eye: 400-700 nanometres
• Speeds of EM radiation are the same in a vacuum and in air
• When radiation strikes an object, it can be:

  • Transmitted
  • Reflected
  • Absorbed
• Radio waves can be produced by oscillations in an electrical circuit
• Radio waves can create an alternating current in a circuit by inducing oscillations with the same frequency as the waves themselves
• Gamma rays originate from changes in the nuclei of atoms
• Ultraviolet waves can cause:

  • Premature aging of the skin
  • Increased risk of developing skin cancer
• 1. rays and Gamma rays can cause:

  • Mutations in genes
  • Increased risk of developing various cancers
• Infrared waves can cause burns to skin/tissue