Aileen Kang - Gizmo Lab Photoelectric Effect Student 2022

The blue dots on the metal plate are electrons. What happens when the photons hit the electrons? When the photons hit the electrons, half of the Electrons were knocked off of the potassium. 2. What happens when the electrons reach the light bulb? When the electrons reach the light bulb, the light bulb lights up. When electrons reach the light bulb they complete a circuit, causing the bulb to glow briefly. Activity A: Wavelength and flux Get the Gizmo ready: ● Check that the Voltage is 0.0 volts and Potassium is selected. Introduction: Through the centuries, many scientists have debated whether light is a wave or a stream of tiny particles. In the 1800’s, most scientists agreed that phenomena such as refraction and diffraction supported the “light as a wave” theory. However, Albert Einstein’s explanation of the photoelectric effect showed that light can act like a stream of particles as well. Question: What factors affect the ability of light to free electrons from a metal surface? 1. Observe: Click Flash the light with a variety of wavelength values. What do you notice? I notice that the speed of the electron being knocked off gets slower as the wavelength increases and gets faster as the wavelength decreases. 2. Observe: The photon flux is a measure of how bright the light is. It is equal to the number of photons that are released in a given time. It is given as photons (γ) per millisecond (ms). Click Flash the light with a variety of Photon flux values. What do you notice? I notice that the Photon flux determines how many electrons get knocked off. 3. Form hypothesis: Answer the following questions based on what you have observed so far. A. Which factor determines how many photons will strike the metal? The factor that determines how many protons will strike the metal is how bright the original light is that is going to bounce off of the metal. Explain: The number of Photons are directly correlated to the brightness of the light and the more Photons there are the more electrons will bounce off of the metal. B. Which factor determines how much energy each photon has? The factor that determines how much energy each photon has is wavelength. Explain: The shorter the wavelength is, the faster the electrons get knocked off. 4. Investigate: Set the Photon flux to 1 γ/ms. Use the Gizmo to find the longest wavelength that will dislodge an electron from the metal surface. What is this wavelength? The longest wavelength that will dislodge an electron from the metal surface is 530nm. 5. Predict: Set the Wavelength to 540 nm. What do you think will happen if you flash the light with a photon flux of 1 γ/ms? What if you flash the light with a flux of 10 γ/ms? This study source was downloaded by from CourseH on :53:36 GMT -06:00 I think that if you flash the light with a photon flux of 1 γ/ms the electrons will not bounce off because of the lack of energy. I also think that the light with a flux of 10 γ/ms will not bounce off because no matter how many photons a light has, there will not be enough energy to convey it. 6. Test: Click Flash the light with a Photon flux of 1 γ/ms and again with a flux of 10 γ/ms. What happened? No electrons were knocked off of the metal. 7. Explore: Set the Wavelength to 400 nm. Experiment with different photon fluxes. A. Does the photon flux affect how many electrons are emitted? Yes, the photon flux affects how many electrons are emitted. Explain: The number of Photon fluxes determine how many electrons are knocked off. B. Does the photon flux affect the energy (speed) of the emitted electrons? The photon flux does not affect the energy of the emitted electrons. Explain: The photon flux doesn’t accept the energy of the electrons, they affect the number of electrons. The wavelength affects the energy of the emitted electrons. 8. Infer: For mechanical waves, such as sound waves or ocean waves, increasing the intensity of the wave increases both the amplitude (height) of the wave and the energy it carries. In that situation, a lowfrequency but high-intensity wave should have the same effect as a high-frequency but low-intensity wave. How does light behave differently from this model? Explain? Light behaves differently from this model because mechanical waves increase in energy while light waves increase in photons. 9. Think and discuss: How is firing photons at the surface of a metal analogous to rolling different types of balls at a set of bowling pins? Explain? Firing photons at the surface of a metal is analogous to rolling different types of balls at a set of bowling pins because it doesn’t matter how many you fire, the only way to affect the bowling pins is to have the right amount of energy and the right type of ball. Activity B: Voltage gradients Get the Gizmo ready: ● Set the Wavelength to 300 nm, the Photon flux to 10 γ/ms, and the Voltage to 0.0 volts. ● Turn on Show voltage gradient. Introduction: The electrons that are freed from the surface of the metal have a specific amount of kinetic energy. Faster electrons have greater energies than slower ones. The energy of emitted electrons is measured by setting up an electrical field that opposes their motion. The voltage of the field is a measure of its strength. Goal: Use a voltage gradient to measure the energy of emitted electrons. 1. Observe: Check that Potassium is selected. Click Flash the light and observe the emitted electrons. Increase the Voltage to 1.5 volts, and click Flash the light again. How does the electrical field affect the motion of the emitted electrons? The electrical field affects the motion of the emitted electrons by slowing them down when they are knocked off of the metal. The further the electrons go, the slower they get. 2. Measure: The energy of an emitted electron is measured in electron volts (eV). An electron with an energy of 1 eV can overcome an electrical field of 1 volt. In the Gizmo, increase the voltage until you find the highest voltage that still allows the electrons to reach the light bulb. What is this value? 1.8 volts. This is equal to the energy of the emitted electrons in eV.