When heat broke the old physics

Science · Quantum & Modern Physics · ages 18-19

Name ______________________ Date ____________

Hotter bodies glow brighter and their peak slides toward shorter wavelengths.
Circle one: True False
What is a blackbody?
- A perfect absorber and emitter of radiation
- An object that emits no radiation at all
- A body painted black for decoration
What was the ultraviolet catastrophe?
- A failed satellite launch
- The classical prediction of infinite short wavelength power
- A gap in the Sun spectrum
A star peaks near 560 nanometers in the visible range. What does that tell you?
- Its surface temperature follows from peak times temperature equals the constant
- Its exact age in years
- Its distance from Earth
How did Planck remove the short wavelength failure?
- By banning short wavelengths from nature
- By letting energy swap in chunks of h times f
- By cooling every hot object down
How does total radiated brightness grow with temperature?
- As temperature to the fourth power
- In direct inverse to temperature
- It stays flat at all temperatures
Body A glows red and body B glows blue white. Which is hotter, and how do you know?
- A is hotter, since red means more energy
- Both must share one temperature
- B is hotter, since the peak slides to shorter wavelength with temperature
Peak wavelength times temperature equals 3 in some units, and a body peaks at wavelength 1. What is its temperature?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

True · Rising heat lifts the whole curve and pushes its peak from red toward blue.
A perfect absorber and emitter of radiation · It takes in everything that arrives and emits with matching eagerness.
The classical prediction of infinite short wavelength power · Old theory said power should explode at short wavelengths, which experiments refute.
Its surface temperature follows from peak times temperature equals the constant · Peak wavelength times temperature is fixed, so the peak reveals the temperature.
By letting energy swap in chunks of h times f · Chunked exchange makes costly high frequency modes too pricey to fire often.
As temperature to the fourth power · A small rise in heat makes a much bigger rise in glow through the fourth power.
B is hotter, since the peak slides to shorter wavelength with temperature · Blue white peaks sit at shorter wavelengths, which only hotter bodies reach.
3 · Divide the constant by the peak: 3 divided by 1 gives temperature 3.