Vocabulary: electron volt, frequency, intensity, photoelectric effect, photon, voltage, wavelength, work function Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Suppose you went bowling, but instead of a bowling ball you rolled a ping pong ball down the alley. What do you think would happen? No strike would be achieved,since the ping pong ball is not big enough to knock off any of the pins 2. Suppose you rolled a lot of ping pong balls at the bowling pins. Do you think that would change the results of your experiment? Explain. Same event will take place,none of the pins would be knocked,because the base are small,but knock off a pin the need to generate a lot of momentum and velocity,which can only be achieved in a vacuum Gizmo Warm-up The photoelectric effect occurs when tiny packets of light, called photons, knock electrons away from a metal surface. Only photons with enough energy are able to dislodge electrons. In the Photoelectric Effect Gizmo™, check that the Wavelength is 500 nm, the Intensity is 50%, the Voltage is 0.0 volts, and Potassium is selected. Click Flash the light to send photons of light (green arrows) toward the surface of a metal plate encased in a vacuum tube. 1. The blue dots on the metal plate are electrons. What happens when the photons hit the electrons? As a result they move across the the gradient and head towards the metal plate. 2. What happens when the electrons reach the light bulb? They turn on bulbs When electrons reach the light bulb they complete a circuit, causing the bulb to glow briefly. Activity A: Wavelength and intensity Get the Gizmo ready: · Check that the Voltage is 0.0 volts. · Check that Potassium is selected. Introduction: Through the centuries, many scientists have debated whether light is a wave or a stream of tiny particles. In the 1800s, 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: How does the wavelength and intensity of light affect its ability to free electrons from the surface of a material? 1. Observe: Click Flash the light with a variety of Wavelength values. What do you notice? lower wavelength equals higher speeds and increased speed of electron 2. Observe: Click Flash the light with a variety of Intensity values. What do you notice? That is the controlling factor,it controls number of electron will strike the metal 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? Intensity Explain: the amount of electrons and photons shot at the electrons,correlated with higher intensity B. Which factor determines how much energy each photon has? _Wavelength Explain: less wavelength equated to a quicker movement of electron 4. Investigate: Set the Intensity to 10%. Uses the Gizmo to determine the largest wavelength that will dislodge an electron from the surface of the metal. What is this value? _530nm 5. Predict: Set the Wavelength to 540 nm. What do you think will happen if you flash the light with an intensity of 10%? What will happen if you flash the light with an intensity of 100%? At both instance little no effect will happen.