Black Body Radiation and Wave vs. Particle
In-Class Worksheet
Using Weins Law Chart to Answer questions.
1) Graphical Reasoning: The temperature of the sun is around 5700 K. What does this mean about the types of light the
sun emits?**
2) Synthesis: What color is the sun (not as silly as it sounds, we know what color the sun appears to us, what color is it
according to the graph? Why the difference)?**
3) Synthesis: Why are incandescent bulbs so inefficient to use?***
Problem 4- Double slit experiment. Draw what the expected outcome of each situation
Critical thinking question: You learned about the double slit experiment. Where Young shined a light through slits and
observed an interference pattern. This told us that light was wave-like. But in science its always very important to know
what sort of data you’d expect for different hypothesis. Because of lights wavelike nature it created interference
patterns, but what would happen if it wasn’t? I did B for you to help explain what I’m looking for. ****
A) Light is only a particle, 1 slit.
B) Completed Example: Light is a particle, 2 slits.
Model of set up. Line shines through right, and onto the screen on the left. This leaves two lines on the film as shown on
the left. (For the ones you do you are welcome to just draw whats on the screen, I just did this for explanation
purposes).
Black Body Radiation and Wave vs. Particle
C) Light is only a wave, 1 slit.
D) Light is only a wave, 2 slits.
Problem 5- Photoelectric effect experiment. Questions you should be able to complete and we will cover throughout
class. (In no particular order) Note: Remember the PHET demo online. **
A) Under the threshold frequency, if the intensity is increased, what happens to the electrons?
B) Over the threshold frequency, if the intensity is increased, what happens to the electrons?
C) Under the threshold frequency, if the frequency is increased, what happens to the electrons?
D) Over the threshold frequency, if the frequency is increased, what happens to the electrons?
E) Under the threshold frequency, if the wavelength is increased, what happens to the electrons?
F) Over the threshold frequency, if the wavelength is increased, what happens to the electrons?
G) What is true at the threshold frequency?
H) If you change the metal, what changes? How does that affect the rest of the variables in the experiment?
Black Body Radiation and Wave vs. Particle
The work function for magnesium is 5.90x10-19 J. **
6) What is the threshold frequency?
7) Calculate the kinetic energy of the ejected electron if the light of frequency 1.80x1015 s-1 is used for irradiating the
metal.
8) Calculate the velocity of the ejected electron if the light of frequency 1.80x1015 s-1 is used for irradiating the metal.
9) Challenge Question:4.5 star difficulty (problem solving itself isn’t particularly difficult but the complexity of the
wording and problem makes it more difficult than normal work).
The electron affinity of thulium has been measured by laser photodetachment electron spectroscopy. In this technique a
gaseous beam of anions of an element is bombarded with photons from a laser. The photons eject electrons from some
of the anions and the energies of the ejected electrons are detected. The photons had a wavelength of 1064nm and the
ejected electrons had an energy of 0.137 eV. Although the analysis is somewhat more complicated, we can obtain a
rough estimate of the electron affinity as the difference in energy between the photons and the energy of the ejected
electrons. What is the electron affinity of thulium in KJ/mol (1.602x10-19J =1 eV).