1. Photocell Foundations of Technology Photocell © 2013 International Technology and Engineering Educators Association, STEM  Center for Teaching and Learning™ Foundations of Technology Teacher Resource Unit 4 Lesson 4

2. Objective: 1.You will observe that a photocell is able to vary its resistance with the amount of light that strikes it.

3. You will need the following parts from your kit: 1.Breadboard 2.Photocell 3.1 LED (light emitting diode) 4.1 wire 5.9 volt battery lead 6.9 volt battery

4. Use this schematic to construct the experiment. + - Flow of current 9 volts Quick Check: Your circuit should like this one. Photocell

5. This circuit will light a LED. 1.The greater the electron flow the brighter the light. 2.Electrons flow from the battery through the LED, then the photocell and finally back to the battery. 3.The greater the resistance, the fewer electrons will flow. 4.Photocells adjust the amount of resistance according to the amount of light that strikes the cell.

6. 1.Connect the 9 volt battery. 2.Observe the brightness of the LED. 3.Cover the photocell with your finger. 4.Observe the brightness of the LED. 5.Carefully shadow the photocell so that a little amount of light is able to strike the cell. 6.Observe the brightness of the LED. Troubleshooting: 1.If the LED does not light up, check to make sure it is in correctly. 2.Check the battery. Does it have voltage? 3.Are there any breaks in the circuit? 4.You may need to get a flashlight or other bright light if the classroom is too dark.

7. By completing this experiment, you should have noticed the light from the LED grew dimmer as you changed the amount of light that hit the photocell. In complete sentences, write what you learned about a photocell in a circuit.