B. Discover Me (Photoelectric Effect) More I. Objectives. Relate and discuss the relationship between frequency and intensity of the photon of light to the kinetic energy and number of the ejected photoelectrons/photoelectron current. II. Materials Computer Unit or Laptop (with online access or saved interactive simulation on photoelectric effect) Ill. Procedure 1. Log on to the Internet and open this URL: http://www.Ipscience.fatcow.com/mgagnon/Photoelectric Effect/photoelectriceffect1.htm (Note: If the simulation has been downloaded and saved by the teacher in the computer, the students will just be instructed to open the simulation and then explore it.) 2. Click the lamp to turn on the light. When reading currents, click on the red button each time the brightness or color is changed. Read the texts so that you will be guided properly. Ask your teacher for assistance when necessary. (Note: The animation shown is a representation of the photoelectric effect. The large oval with an opening represents a tube with a window to let light in and two metal plates on either end. When light from the lamp enters the opening and hits the plate on the left, electrons are emitted. They cross the tube and hit the plate at the right end of the tube. A current is then measured by the ammeter. The wave theory of light says that since light is a wave, the energy of the light (wave) depends on the amplitude (or brightness) of the light (wave). The kinetic energy of the resulting electrons (called photoelectrons) is equal to the energy of the incoming light minus the amount of energy needed to free the electrons from the atoms of the plate (called the work function). The kinetic energy of the photoelectrons can be experimentally measured by using a battery to make the plate on the right negatively charged. The electrons can still hit the plate if they have enough energy. As the plate is made more and more negative, fewer and fewer electrons have enough energy to hit the plate. Finally, the plate can be made so negative that even the electrons with the most energy are unable to hit the plate and the current in the circuit (measured by the ammeter) goes to zero. The negative voltage that causes the current to go to zero is called the stopping potential). 3. Try each of the experiments given in the simulation and answer the questions on your answer sheet. Experiment #1: Change the color in order from blue down to red. Observe and take note what happens. Experiment #2: bet the color to blue and change the brightness. Observe and take note what happens. Experiment #3: Read the definition of stopping potential above. Set the color to blue and the brightness to High. Click the battery button then click each battery setting in order from low voltage to high voltage. Find the voltage that causes the current to go to zero and record it on your answer sheet. Repeat this for each color. Remember to click the red battery button every time you change the light color. Observe and take note what happens. Experiment #4: Do an experiment to answer the following question. Observe and take note what happens. IV. ANALYSIS/OBSERVATION Experiment #1 What effect does changing the color of light have on the ejected photoelectrons? Experiment #2 What effect does changing the brightness of the light have on the photoelectrons? Experiment #3 What effect does changing the color of light have on the stopping potential? Experiment #4 For a given color of light, does changing the brightness change the stopping potential? Generalizations