Unexpected Results
What photoelectric experiments revealed about frequency, intensity, and electron emission
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Unexpected
As long as you are 1. When you brighten the light source
Get more electron emission
... but
not faster
(more energetic) electrons!!!!
Results Contradict
Wave Theory!
According to
Increasing Brightness,
Should Increase Kinetic Energy
- It Didn't!!
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Light above the threshold frequency hits a metal. If the light is made brighter, what happens?
2. Making the light brighter does NOT change which of these?
3. According to wave theory, brightening the light should have…
4. The intensity of light shining on a metal is doubled (above threshold). The emitted electrons' maximum kinetic energy…
5. Why were the photoelectric results called "unexpected"?
The Gold Foil Experiment
In 1909, Rutherford’s team fired positively charged alpha particles at a very thin sheet of gold foil. Almost all passed straight through. A very small fraction were deflected at large angles, and a few bounced almost straight back.
Which conclusion about the atom is best supported?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C2. Which model did this experiment disprove?
C3. An alpha particle (charge 3.20 × 10−19 C) is 1.0 × 10−13 m from a gold nucleus (charge 1.26 × 10−17 C). Substitute numerical values into a mathematical representation that can be used to determine the magnitude of the electrostatic force between them. Then calculate the force. (k = 8.99 × 109 N·m2/C2)
C4. An alpha particle moves to the right, heading straight toward a gold nucleus that is directly to its right. When the alpha particle is 5.0 × 10−14 m from the nucleus, choose the direction of the electrostatic force on the alpha particle, and determine its magnitude. (Use the charges and k from the previous question.)
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C5. Why was a very thin foil used?
C6. Rutherford concluded that (1) most of the atom is empty space and (2) the atom’s positive charge and most of its mass are concentrated in a tiny nucleus. Identify the evidence from the experiment that supports each conclusion.