# NASA - National Aeronautics and Space Administration

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Rain Sensor
Teacher Section

Objective: To build a simple sensor to detect rainfall and to brainstorm ways a sensor can activate simple devices.

Subject(s): Science, Technology
Prep Time: 10-30 minutes
Duration: One class period
Materials Category: Special

National Education Standards
Science
Physical Science
Transfer of energy

Technology Literacy
Students will develop an understanding of and be able to select and use information and communication technologies.
Communication systems are made up of a source, encoder, transmitter, receiver, decoder and destination.
Materials: (Per Group)
• Six-volt lantern battery
• Wire (Wires with alligator clips are recommended.)
• Switch
• Six-volt light bulb and socket
• Small piece of wood [about 4 inches (in) by 4 in, or 10 centimeters (cm) by 10 cm]
• Thumbtacks
• Heavy duty aluminum foil
• Spray bottle filled with water
• Student Page
Pre-lesson Instructions
• This lesson can be used as a demonstration, an exploration activity for a science project or an introductory activity for a unit on circuits and electricity.
• Build a simple circuit (like the one pictured below) to demonstrate how closed and open circuits behave.
• Adding salt to the water will help conductivity (useful for younger grades), which will help ensure success of sensor circuit.
Background Information

Sensors are usually designed to monitor one thing at a time. If more than one condition needs to be monitored, more than one sensor is used. Sensors can measure light, temperature and other things. Simple sensors will basically answer a yes or no question [Is the temperature above 90 degrees Celsius (194 degrees Fahrenheit)?]. The computer monitoring the sensor will decide how to use this information.

Guidelines
1. Discuss the importance of sensors. Bring up the idea that sensors can be placed where it would be impossible or impractical for a human to observe environmental changes.

2. Image to right: This shows a simple circuit with a switch. Credit: NASA

3. Demonstrate the simple circuit to the class. Encourage them to observe what happens when the circuit is turned on, creating a closed circuit. What happens when the circuit is turned off, creating an open circuit?

4. Tell the students they will use a simple circuit as a guide to build a sensor to detect rain.

5. The simple detector they will use will be two strips of metal with a very narrow gap between them. When raindrops fall on and bridge the gap, they will complete (close) the circuit, turning on the light.

6. Image to right: This shows a simple circuit with a sensor. Credit: NASA

7. Discuss procedure and safety instructions with students.

8. To test the circuits, spray them with a spray bottle. (BE CAREFUL TO ONLY SPRAY THE SENSOR!)

9. If the wood is absorbing the water, slip a thin piece of plastic underneath the metal strips.

10. To make sure the connections on the circuit are working correctly, use a paper clip to bridge the gap between the pieces of foil. This should close the circuit and cause the light to glow.

Discussion/Wrap-up
• After cleanup, discuss the activity/demonstration.
• Brainstorm ideas of where this simple sensor could be useful. What could you replace the light with to make it more useful? (One idea is to replace the light with a motor to close a sunroof if it starts to rain.) Be creative.
• What other things might close the gap, causing the sensor to turn on when no rain is present?
• Examine a more complex sensor (where the detector is more complex) such as one contained in a fire alarm. (Different types are designed to detect different events.)

Extensions

• Display a variety of other electronic materials for students to explore and from which to build other sensors. (A burglar alarm with a pressure-sensitive "switch" and a buzzer attached to a doorway would be fairly simple.)
• Set up a real classroom sensor that can be placed outside to monitor the weather.
• Determine which student group built the most sensitive sensor. Why could a sensor that is too sensitive not be useful?
• Have students draw their designs and research their inventions on the Internet to see if they already exist.

Rain Sensor Student Page