Introduction to Modern Physics
Why classical physics needed new ideas about light, matter, and energy
|
showmethephysics.com / Assessment
Modern Physics - 20th Century
I. Dual Nature of Light - Light appears to exhibit 2 characteristics:
Wave or Particle????
A. Review - 19th Century
Experiments Supporting Wave Theory
1) Interference - "Double Slit Exp." - constructive/ destructive
2) Polarization - "Filtering of Light - Light waves have orientations
| Onsite Version |
3) Diffraction - Spreading out of Light behind a barrier
4) Doppler - Color Shift of Light - "Blue to, Red Away"
Review Explain This!
Show
Me Physics School blocks YouTube? Use the link below
|
|||||||||
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Young's double-slit experiment showed bright and dark bands of light. Which wave behavior does this demonstrate?
2. Polarization of light is evidence that light waves have what property?
3. Light spreading out after passing the edge of a barrier is called…
4. A galaxy is moving away from Earth. Its light will appear…
5. Why couldn't a picket fence actually polarize light?
Cracks in Classical Physics
Around 1900, physicists had very successful models: Newton’s laws and the wave model of light. But several experimental results could not be explained by these classical models, which led to quantum physics and relativity.
Which observation could not be explained by the classical wave model of light?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. Planck proposed that light energy comes in quanta with E = hf. Violet light has a frequency of 7.5 × 1014 Hz. Substitute numerical values into a mathematical representation that can be used to determine the energy of one quantum of violet light. Then calculate the energy. (h = 6.63 × 10−34 J·s)
C2. How do scientists respond when reliable experimental evidence conflicts with an accepted model?
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. Place a check mark in three boxes to indicate observations from around 1900 that classical physics could not explain.
C5. When is classical (Newtonian) physics still an excellent model?
C6. Choose one experimental result described on this page. Describe what classical physics predicted and explain how the actual result led scientists to change their model.