Complete the activities below by using the resources listed to the right. Write your answers on a sheet of paper or in your course pack.
The purpose of the following activity is to construct a deeper understanding of the interaction of electromagnetic radiation and matter by investigating the photoelectric effect. Let’s start by engaging with a simulator.
Spend some time exploring the simulator at http://phet.colorado.edu/en/simulation/photoelectric.
- What happens when you change the metal?
- What happens when you change the wavelength of light?
- What happens when you change the intensity (brightness) of light?
- Explore the effects of changing the wavelength and the intensity. Select sodium. Set intensity at 25%. Set color at blue, 455 nm. Set the voltage at 0.00V. Press start. What do you see?
- What happens when increase “intensity” (Brightness) to 50%?
- What happens when increase “intensity” to 90%?
- Reduce intensity to 25%. Set color at red, 700 nm? Observation?
- Increase intensity to 50%. Observation?
- Increase intensity to 90%. Observation?
The purpose of this activity is to continue to explore this concept using the simulator at http://phet.colorado.edu/en/simulation/photoelectric. Explore the effects of metal identity and wavelength.
- Go back to blue, 455 nm. Switch metal to zinc. Observation?
- Increase wavelength to IR region. Observation?
- Decrease wavelength to 280 nm. Observation?
- Decrease wavelength to 185 nm. Observation? Speed of e-?
The purpose of this activity is to summarize your explorations in Activities 1 and 2.
- Were there any differences or similarities between sodium and zinc in this experiment? If so, can you describe them?
- How did changing the wavelength of light (at a constant intensity) affect the electrons coming off of the surface of the metal? When there were originally no electrons? When there were already some electrons being ejected?
- At a constant wavelength, how did increasing the intensity affect the removal of electrons? When there were originally no electrons? When there were already some electrons being ejected?
The purpose of this activity is to build your understanding of the photoelectric effect.
- Sketch the shape of the graph of the kinetic energy of the ejected electrons versus the frequency of the incident radiation for sodium, and summarize the interpretation of the graph. Note on the sketch the frequency that corresponds to the work function for sodium.
- In 1905, Einstein published his landmark paper in which he interpreted Planck’s photoelectric effect experiment by explaining that exhibited light behaves both like an wave and as a particle called a photon. A photon is defined as:
- Summarize here Einstein’s interpretation of the results of Planck’s experiment, including the equation relating the energy of the photon to the frequency of the electromagnetic radiation, for which he was awarded the Nobel Prize in Physics in 1921.
The purpose of this activity is to perform calculations with the photoelectic effect.
- Determine the energy of a photon with a frequency of 3.17 x 1017 Hz.
- Define each of the symbols in the following equation.
Ev = Φ + KEe-
- The work function of chromium metal is 4.37 eV. What wavelength of radiation must be used to eject electrons with a velocity of 2500 km/s?
- In summary, the major conceptual breakthrough developed from the interpretation of the photoelectric effect experiments was the dual nature of light – that is light has both wavelike and particle-like properties. A packet of quantized energy associated with electromagnetic radiation is called a ______________________________.
The important concept concerning chemistry that you should commit to memory is the idea that if a photon of sufficient energy collides with electrons in the associated matter, an electron can be ejected from the matter!