8.14 - Absorbing Radiation (Infrared & Black Body)

• What does every object do with electromagnetic radiation?

  Absorbs and emits electromagnetic radiation
• Why does an object warm up when it absorbs radiation?

  Because radiation is pure energy
• What happens to an object when it emits radiation?

  It cools down
• How does the balance of absorbing and emitting radiation affect temperature?

  It determines if the object warms or cools
• What happens to a hotter object like a cup of tea in terms of radiation?

  It emits more radiation than it absorbs
• What occurs with a cooler object like an ice cube regarding radiation?

  It absorbs more energy than it emits
• What happens when an object absorbs and emits the same amount of energy?

  It stays at the same temperature
• What is the term used to describe the power of radiation per unit area?

  Intensity
• What does intensity measure in terms of radiation?

  Energy transferred to a given area over time
• What types of electromagnetic radiation should we focus on?

  • Ultraviolet radiation
  • Visible light
  • Infrared radiation
• How does the emitted radiation graph change with temperature?

  Higher temperature shifts curve up and left
• What does a hotter object like burning coal emit compared to a cooler object?

  More radiation and shorter wavelengths
• What happens to the color of a Bunsen burner flame as it gets hotter?

  It changes from orange-red to blue
• Why can't we see the emitted radiation from room temperature objects?

  It's all in the infrared range
• How does the Earth interact with electromagnetic radiation from the sun?

  It absorbs and emits infrared radiation
• What happens to the Earth's temperature during the day?

  More energy is absorbed than emitted
• What occurs to the Earth's temperature at night?

  Less energy is absorbed than emitted
• Why does the overall temperature of the Earth stay constant?

  Some parts are always in the sun
• Objects that are hotter than their surroundings emit ________ radiation than they absorb.

  more
• Intensity is a measure of the power of the radiation, per unit area.
• An object at room temperature emits mostly:

  Infrared radiation
• As the temperature of an object increases, the intensity of the radiation emitted by the object ________.

  increases
• As the temperature of an object increases, the wavelength of radiation emitted by the object decreases.
• At night time:

  • The land absorbs less energy than it emits
  • The lands local temperature decreases
• Cosmic microwave background radiation (CMBR)

  Cosmic microwave background radiation (CMBR) is electromagnetic radiation that is observed in all directions.

  Initially radiation from the big bang was incredibly hot. 

  As the universe has expanded and cooled, the background radiation has dropped in frequency.
• Red shift equation

  The redshift equation allows us to calculate the recessional velocity of a galaxy based on the observed shift in wavelength of light from that galaxy. 

  λ0​Δλ​ = cv​

  Where:

  • Δλ = the difference between the observed wavelength and the original wavelength. It is the amount that the wavelength has been shifted.
  • λ is the original wavelength of light. 
  • v = recessional velocity of the galaxy.
  • c = speed of light in a vacuum, 300,000,000 m/s.
• Which side of the absorption spectra above has the longer wavelength?

  The red side on the left

  
• Which of these provides evidence for the Big Bang?

  Blue-shift

  Doppler effect 

  Red-shift

  Red-shift
• Red-shift is when light from distant galaxies show an absorption spectra pattern that has been shifted to:

  The red side of the spectra
• How many galaxies show a red-shift?

  • Nearly all
  • The light reaching us from almost all galaxies is red-shifted as almost all galaxies are moving away from us. 
• Red-shift occurs because the light emitted by an object moving away from us will be stretched. The stretching causes the light's wavelength to increase. The faster an object moves away from us, the larger the red shift.
• Which is the correct explanation for why galaxies are moving away from each other?

  Space and the universe itself is expanding and this makes galaxies further apart
• What is the basic idea of the Big Bang theory?

  The Universe expanded from a single tiny point of high density and pressure
• Give one strength and one weakness of the balloon model in representing the idea of an expanding Universe.

  • Strength - As the balloon expands the dots get further apart, which represents the galaxies moving apart
  • Weakness 1 - The dots are only on the surface of the balloon, whereas galaxies are throughout the universe
  • Weakness 2 - There is a limit to how far the balloon can expand before it bursts
• What evidence supports the big bang theory?

  Red-shift of light from distant galaxies
• What evidence supports the big bang theory?

  Red-shift of light from distant galaxies
• What does red-shift in light from galaxies indicate?

  Galaxies are moving away from us
• What does red-shift in light from galaxies indicate?

  Galaxies are moving away from us
• What does the observation of red-shift suggest about the universe?

  The universe is expanding
• What does the observation of red-shift suggest about the universe?

  The universe is expanding