Wien's Displacement Law

• What does Wien’s Displacement Law describe?

  Relationship between wavelength and temperature

  
• What type of radiation do all bodies emit?

  Thermal radiation in electromagnetic waves
• What is an ideal black-body radiator?

  Absorbs and emits all wavelengths
• How do stars relate to black-body radiators?

  Stars are the best approximation of black bodies
• What determines the characteristic spectrum of radiation emitted from a black body?

  The temperature of the black body alone

  
• What does the black-body radiation curve represent?

  Intensity against wavelength

  
• What happens to the peak of the black-body radiation curve as temperature increases?

  It moves to lower wavelength and higher intensity

  
• What does Wien’s displacement law state about peak wavelength?

  It is inversely proportional to temperature
• How can Wien's displacement law be mathematically expressed?

  λmax ∝ 1/T
• What does λmax represent in Wien's law?

  Maximum wavelength emitted at peak intensity
• What does T represent in Wien's law?

  Surface temperature of an object in Kelvin
• What is the equation for Wien's displacement law?

  λT = 2.9 × 10^-3 m K
• What happens to the wavelength at peak intensity as temperature increases?

  The wavelength becomes shorter

  
• How does the color of stars relate to their temperature?

  Hotter stars appear white or blue
• What are the temperature ranges for different star colors?

  • Blue: >33,000 K
  • Blue-white: 10,000 − 30,000 K
  • White: 7,500 − 10,000 K
  • Yellow-white: 6,000 − 7,500 K
  • Yellow: 5,000 − 6,000 K
  • Orange: 3,500 − 5,000 K
  • Red: <3,500 K
• If an object has a black-body radiation curve at 900 K, what would the curve look like at 650 K?

  It would peak at a longer wavelength

  
• How do you determine which star is cooler using their peak wavelengths?

  Longer peak wavelength indicates cooler star
• What is the maximum emission wavelength of Rigel?

  263 nm
• What is the maximum emission wavelength of Betelgeuse?

  828 nm
• How do you calculate the surface temperature of a star using Wien’s law?

  Rearrange λmaxT = 2.9 × 10^-3 m K
• What is the surface temperature of Rigel?

  11,000 K
• What is the surface temperature of Betelgeuse?

  3,500 K
• How does the color of stars relate to their temperature in the Orion constellation?

  Cooler stars appear red or yellow
• What are common errors when drawing a black-body radiation curve?

  • Right side steeper than left
  • Right side decreases to zero
  • Curve intersects intensity axis
• What temperature scale is used in Wien’s Law?

  Kelvin (K)
• What should you do if temperature is given in °C before using Wien’s Law?

  Convert it to Kelvin