Photoelectric Effect Ranking Task #1 A potassium atom will eject an electron if illuminated by green light, but not yellow. Rank the energy of the electron ejected from potassium atoms if illuminated by the following colors: A B C D E F Red Orange Yellow Green Blue Violet Energy: Greatest _______ _______ _______ _______ _______ _______ Least OR… All energies are equal _______ OR… All energies are zero _______ Explain your reasoning: How sure are you of your ranking? (circle one) Basically Guessed 1 2 3 4 5 6 7 8 9 10 Very Sure Photoelectric Effect Ranking Task #2 A particular metal surface will eject electrons through the photoelectric effect if illuminated by photons of 2.6 eV or higher (blue/teal light). The unit “eV” is a unit of energy. Rank the kinetic energy of the ejected electrons if the surface is illuminated by photons of 2.4 eV (green light) with light bulbs of the following intensities: A
B
C
D
E
F
Greatest _______ _______ _______ _______ _______ _______ Least OR… All energies are equal _______ OR… All energies are zero _______ Explain your reasoning: How sure are you of your ranking? (circle one) Basically Guessed 1 2 3 4 5 6 7 8 9 10 Very Sure Photoelectric Effect Ranking Task #3 A particular metal surface will eject electrons through the photoelectric effect if illuminated by photons of 2.6 eV or higher (blue/teal light). The unit “eV” is a unit of energy. Rank the kinetic energy of the ejected electrons if the surface is illuminated by photons of 2.8 eV (deep blue light) with light bulbs of the following intensities: A
B
C
D
E
F
Greatest _______ _______ _______ _______ _______ _______ Least OR… All energies are equal _______ OR… All energies are zero _______ Explain your reasoning: How sure are you of your ranking? (circle one) Basically Guessed 1 2 3 4 5 6 7 8 9 10 Very Sure Photoelectric Effect Ranking Task #4 A particular metal surface will eject electrons through the photoelectric effect if illuminated by photons of 2.6 eV or higher (blue/teal light). The unit “eV” is a unit of energy. Rank the rate at which electrons are ejected if the surface is illuminated by photons of 2.8 eV (deep blue light) with light bulbs of the following intensities: A
B
C
D
E
F
Greatest _______ _______ _______ _______ _______ _______ Least OR… All energies are equal _______ OR… All energies are zero _______ Explain your reasoning: How sure are you of your ranking? (circle one) Basically Guessed 1 2 3 4 5 6 7 8 9 10 Very Sure Photoelectric Effect Conflicting Contentions Task #1 Alice, Bob and Chris are working diligently in the physics lab making a doorbell ‘dinger’ that goes off when a person walks through the door. They are using a photoelectric effect sensor and a green 532 nm laser. According to their plan, when the laser beam strikes the photoelectric sensor, the circuit will detect the beam. When the beam is broken, the circuit will ring a bell. They test their doorbell, and it doesn’t work. Everything is hooked up and aligned, but even when the laser is very close to the photoelectric detector the laser doesn’t seem to have any detectable effect on the photocell. The three students make the following statements about how to fix their doorbell. Alice: I think the green laser doesn’t have enough energy, so we should try a blue laser. Bob: I think the green laser is too weak, so we should try a higher power green laser. Chris: I think the green laser has a wavelength that is too short. We should try a longer wavelength red laser. Which of these students could be correct? Alice: ______ Bob: ______ Chris: ______ Explain your answer below. Teacher’s Notes You may need to show students how to show ties in a ranking task. Answer Key Ranking Task #1: [Greatest] F E D CBA [Least] Note: C, B, and A are all equal to zero. Ranking Task #2: [Greatest] ABCDEF [Least] Note: ALL values are zero. Ranking Task #3: [Greatest] ABCDEF [Least] Note: ALL are equal, and greater than zero. Ranking Task #4: [Greatest] F E D C B A [Least] Note: A = 0. Conflicting Contentions Task #1 Alice COULD be correct. If the green laser does not have photons with enough energy to eject electrons from the metal in the photoelectric detector, trying more energetic electrons (such as blue) would make sense. Bob’s suggestion to try a higher power laser would not help if the green laser is not producing any detectable effect when illuminating the photoelectric detector. Chris’ suggestion to try a red laser would not help, as red light has lower energy than green light. If green light would not eject electrons in any detectable way, red light would not do so either.