Edexcel A Level Physics:复习笔记9.12 Wien’s Law

• Wien’s displacement law relates the observed wavelength of light from an object to its surface temperature, it states:

The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the temperature

• This relation can be written as:

• λmax is the maximum wavelength (m) emitted by an object at the peak intensity
• T is the surface temperature (K) of an object

• Wien's Law equation is given by:

λmaxT = 2.9 × 10−3 m K

• This equation tells us the higher the temperature of a body:
  • The shorter the wavelength at the peak intensity, so hotter objects tend to be white or blue, and cooler objects tend to be red or yellow
  • The greater the intensity of the radiation at each wavelength

   

Table to compare surface temperature and star colour

Step 1: Write down Wien’s displacement law

λmaxT = 2.9 × 10-3 m K

Step 2: Rearrange for temperature T

Step 3: Calculate the surface temperature of each star

Step 4: Write a concluding sentence

Betelgeuse has a surface temperature of 3500 K, therefore, it is much cooler than Rigel

The Orion Constellation; cooler stars, such as Betelguese, appear red or yellow, while hotter stars, such as Rigel, appear white or blue