Electromagnetic radiation and heat

• What is heat defined as?

  Energy transferred between systems at different temperatures
• In which direction does heat transfer occur?

  From hotter to colder systems
• What is the unit of heat?

  Joules (J)
• What are the three mechanisms of heat transfer?

  • Conduction: Transfer through physical contact
  • Convection: Transfer by a moving fluid
  • Radiation: Transfer by emission of electromagnetic radiation
• How does conduction occur?

  Through physical contact between materials
• What happens to conduction when temperatures equalize?

  Conduction of heat stops
• What drives convection?

  Density differences in a fluid
• What is an example of convection?

  Hot gases from a fire rising
• How does radiation transfer heat?

  By emitting infrared electromagnetic radiation
• What is required for all mechanisms of heat transfer?

  A temperature difference
• What happens when ΔT equals zero?

  Heat flow ceases
• How is the rate of heat transfer measured?

  In watts (W)
• What does the rate of heat transfer depend on?

  ΔT and specific properties of the transfer mechanism
• What factors affect conduction, convection, and radiation?

  • Conduction: Thermal conductivity, dimensions
  • Convection: Surface area, fluid properties, velocity
  • Radiation: Material type, emissivity, surface area
• What is specific heat capacity?

  Energy needed to change temperature of 1 kg by 1 K
• How is the amount of energy (Q) calculated?

  Q = mcΔT
• How is specific heat capacity (c) calculated?

  c = Q / mΔT
• What is the unit of specific heat capacity?

  J Kg^-1K^-1
• What does power measure?

  The rate of energy transferred
• What is the unit of power?

  Watts (W)
• How is power related to heat transfer (Q)?

  P = Q / t
• What is latent heat?

  Heat energy needed for phase changes
• What is the latent heat of fusion?

  Heat for changing solid to liquid
• How is latent heat of fusion calculated?

  Q = mL_f
• What is the latent heat of vaporization?

  Heat for changing liquid to gas
• How is latent heat of vaporization calculated?

  Q = mL_v
• What is electromagnetic radiation (emr)?

  Radiant energy traveling as waves and particles
• What is wave-particle duality?

  Emr has properties of both waves and particles
• What are photons?

  Particles of electromagnetic radiation
• How do atoms and molecules interact with emr?

  They absorb and/or emit emr
• What is spectra?

  Patterns of absorption and emission of emr
• What is spectroscopy?

  Field interpreting spectra for analysis
• What does UV-VIS spectroscopy cover?

  Wavelengths from ~200nm to 900nm
• What happens when UV and visible light is absorbed?

  Electrons in atoms and molecules are excited
• What is the equation for the speed of light?

  c = λv
• What is Planck's constant (h)?

  6.626 x 10^-34 Js
• What is the speed of light (c)?

  2.998 x 10⁸ m/s
• What is the unit of energy (E)?

  Joules (J)
• What are the properties of different types of electromagnetic radiation?

  • Gamma rays: Highest energy, penetrating radiation
  • X-rays: Penetrating ionizing radiation
  • UV: Causes DNA damage, electronic changes
  • Visible light: Causes electronic changes, photochemical reactions
  • Infrared: Causes vibrational changes in molecules
  • Microwaves: Causes rotational changes in molecules
  • Radio: Lowest energy, longest wavelength
• What is the wavelength range of visible light?

  380-750 nm