physics - light and the electromagnetic spectrum

• describe how a student could use a semi-circular glass block to determine critical angle at a glass-air boundary

  • shine a ray of light into block through the curved surface along a radius
  • move ray box until angle of refraction is 90
  • measure angle of incidence and repeat measurements of critical angle
• define critical angle
• explain why total internal reflection occurs
• state that when light travels from one medium to another, it may be reflected or transmitted (refracted) depending on its speed in those media.
• explain why total internal reflection occurs when light travels from one medium to another with a smaller refractive index
• radio waves and gamma radiation are at opposite ends of the electromagnetic spectrum

  compare how these two electromagnetic spectrums are are produced

  • radio waves often produced intentionally by humans
  • gamma rays often produced spontaneously
  • radio waves are produced by free electrons
  • gamma rays are a result of radio active decay
  • radio waves are produced in electrical circuits
  • gamma rays are produced in the nucleus
• explain why an infrared remote control may not switch on the tv but a radio wave remote control always will

  • infrared is absorbed by the armchair and cannot pass through
  • however radio waves can
  • this is because they have different wavelengths/frequencies
• name the wave

  used in cooking, short-range communication, typical wavelength of 900nm

  infrared
• name the wave

  used in cooking, communication, typical wavelength of 150mm

  microwave
• name the wave

  used in communication, produced by oscillations in electrical curcuits, typical wavelength of 150m

  radiowave
• name the wave

  used in medical scanning, emitted by the nucleus of an atom, typical wavelength of $2.0 x 10^-3$


  gamma
• suggest a benefit to making lenses go dark with ultraviolet light

  UV is most harmful to eyes
• what radiation is electromagnetic and ionising

  gamma
• what radiation travels the shortest difference in air

  alpha
• explain why temperature on vesta does not continue to rise, even though it is absorbing energy from the sun

  vesta also radiates the same amount of energy it absorbs from the sun in the same time
• explain why some food is irradiated with gamma radiation

  • preserves food by killing bacteria
  • very penetrating so reaches all food
• explain what happens to the body if a person has prolonged exposure to gamma rays

  damages cells because it is highly ionising

  can cause cell mutation and cell death
• one way X-rays are useful to humans

  seeing broken bones
• one way X-rays are harmful to humans

  mutates cells
• Gamma rays are highly ionising
• X-rays are moderately ionising
• Visible light is non-ionising
• Ultraviolet (UV) rays are slightly ionising
• Visible light is not ionising at all
• Infrared (IR) waves are not ionising at all
• Infrared radiation is non-ionising
• The higher up on the EM spectrum, the more energy there is per photon.
• The wavelength of visible light ranges from about 400 nm to 750 nm.
• The frequency of visible light ranges from about 8 x 10^14 Hz to 4 x 10^14 Hz.
• X-rays have very short wavelengths and high frequencies.
• Gamma rays have even shorter wavelengths than X-rays, ranging from less than 1 pm to around 100 fm.
• The energy of visible light varies depending on its color, with violet having the highest energy and red having the lowest energy.
• Gamma rays are emitted by radioactive nuclei during nuclear decay or when two atomic nuclei collide at high speeds.
• Gamma rays are also produced by cosmic ray interactions with Earth's atmosphere.
• Gamma rays are also produced by cosmic ray interactions in space.
• Radio waves are used by radio stations to transmit signals over long distances.
• Gamma rays are used in smoke detectors to ionize air molecules and create an electrical current that triggers an alarm if there is no smoke present.
• Gamma rays are used in industrial radiography to inspect materials such as welds, pipes, and castings for defects.
• Gamma rays can penetrate through thick materials like concrete walls and steel doors.
• Ultraviolet radiation is used in tanning beds to simulate sun exposure and promote skin pigmentation.