AGRISCIENCE EXERCISE

PHYSICAL SCIENCES IN AGRICULTURE

Key Concept: Electricity and Electronic Systems

Sub-Concept: What is Electricity?

Agricultural Application: Basic electronic principles are applied in common agricultural equipment.

Exercise: What is Electricity? Generating an Electromotive Force

Applied Principle: Electricity Radiation Magnetism

Goals:

Generate an electromotive force using chemicals, magnetism, heat, and solar radiation.
Construct and understand the action of a primary cell.

Materials:

For all experiments:

Digital multi-meters
Test leads with alligator clips on both ends
No. 18 and 20 flexible wires for connections

Additional equipment for each experiment:

EMF by Chemical Reaction

1 pint saltwater solution in a glass
Electrode set (copper and zinc plates)
1 pint citric acid (lemon juice) in a glass

EMF by Magnetism

Enamel insulated wire
Directional compass
Magnet (permanent, bar type at least 5" long)

EMF by Heat

5" bare copper wire
5" iron wire
Candle

EMF by Solar Radiation

Solar cell
Strong light source

References: Osborne, E., Moss, J., Buriak, P., and Wallace, P. (undated). Physical Science Applications in Agriculture: A New Agriculture Course for Secondary Schools. Urbana, IL: University of Illinois, Urbana-Champaign.

Teacher Preparation Notes:

Make a copies of the student instruction/data sheets for the students.

The instructor may wish to set up a trial run for each part of this activity prior to conducting it in class, in order to anticipate any problems or questions the students may have.

Procedures for Conducting the Activity:

1. Lead the class in a discussion about electricity. This may include ways we use electricity (especially in relation to agriculture), where we get electricity, and how they think electricity is made.

Explain that this activity will give them the chance to see how electricity can be generated in a number of different ways. [NOTE: You may wish to discuss some basic concepts at this point, such as the meaning of "electromotive force" and "resistance".]

2. Divide the class into 4 small groups.

3. Explain that each group will use a different method to produce an electromotive force.

First, each group will conduct the experiment set out for them on their instruction sheets, record the appropriate data, and answer the discussion questions.

Next, they will repeat their experiments as a demonstration to the rest of the class. They are to explain the procedure as they go, then present their findings and discuss the answers to their discussion questions.

4. Provide each group with the appropriate instruction/data sheet and necessary materials.

5. Allow the groups to proceed with their experiments, carefully supervising their progress. [The students may need help when answering their discussion questions.]

6. Once all groups have finished, instruct them to clean up and organize their materials to prepare for the class demonstrations.

7. Have each group present its experiment to the class. Make sure that all points are satisfactorily discussed and demonstrated.

AGRISCIENCE EXERCISE

- What is Electricity? Generating an Electromotive Force -

Student Data/Instruction Sheet

Group 1: EMF by Chemical Reaction

Procedures:

1. As a group, read the entire experiment before proceeding further.

2. Gather all necessary materials for the experiment, as listed below:

Digital multi-meter
Test leads with alligator clips on both ends
Electrode set (copper and zinc plates)
1 pint saltwater solution in a glass
1 pint citric acid (lemon juice) in a glass

3. Attach a test lead to a copper strip. Attach another test lead to a zinc strip.

4. Lower the electrodes into the saltwater solution.

5. Set the voltmeter to read 0-5 volts DC and connect the meter to the cell terminals.

6. Record the cell's voltage output on the table on the next page.

7. Remove the electrodes from the solution.

8. Thoroughly rinse the electrodes to remove all traces of the saltwater solution.

9. Next, use the citric acid solution...

10. Connect the meter to the terminals and record the voltage reading.

11. Remove the electrodes from the solution and clean with water.

Data Summary and Analysis Table

Cell Unit Solution Electrode Polarity Voltage Output

Zinc
Copper
Saltwater Zinc: __________
Copper: _______

Zinc
Copper
Citric Acid Zinc: __________
Copper: ________

14. Compare the polarity of the electrodes and the voltage outputs. What does this mean?

________________________________________________________________

15. Based on your findings, how can the use of zinc and carbon be justified for active elements in commercial dry cells?

________________________________________________________________

16. Clean up your area and materials; set up to start the exercise over so that you can present it to the class.

Take some time to organize your presentation. Make sure that everyone in your group has the chance to participate. For example, one person could explain the purpose of the activity, someone could discuss the materials needed to carry out the exercise, one or more could perform the activity while someone discusses the steps in the procedure, and someone should discuss the answers to the questions.

17. At the appropriate time, you will be asked to demonstrate your experiment for the class. When you have finished, it is your responsibility to clean up and put away the materials you used.

AGRISCIENCE EXERCISE

- What is Electricity? Generating an Electromotive Force -

Student Data/Instruction Sheet

Group 2: EMF by Magnetism

Procedures:

1. As a group, read the entire experiment before proceeding further.

2. Gather all necessary materials for the experiment, as listed below:

Digital multimeter
Test leads with alligator clips at both ends
Directional compass
Permanent, bar type magnet, about 5" long
Enamel insulated wire

3. Wrap a piece of insulated wire around your hand, forming a coil.

4. Connect each end of the coil to a clip lead.

5. Connect the leads to a multi-meter.

6. Find the North end of the magnet, using the compass.

7. Push the North end of the magnet into the coil; observe and record the action of the meter.

_________________________________________________________________

8. Now, hold the magnet still inside the coil; observe and record the meter reading.

_________________________________________________________________

9. Push the opposite (South) end of the magnet into the coil; observe and record the meter reading.

_________________________________________________________________

10. Quickly withdraw the magnet from the coil. Record what happens to the meter.

_________________________________________________________________

11. What conclusions can you draw from the results of your experiment?

_________________________________________________________________

12. Clean up your area and materials; set up to start the exercise over so that you can present it to the class.

13. At the appropriate time, you will be asked to demonstrate your experiment for the class. When you have finished, it is your responsibility to clean up and put away the materials you used.

AGRISCIENCE EXERCISE

- What is Electricity? Generating an Electromotive Force -

Student Data/Instruction Sheet

Group 3: EMF by Heat

Procedures:

1. As a group, read the entire experiment before proceeding further.

2. Gather all necessary materials for the experiment, as listed below:

Multitester
Test leads with alligator clips at both ends
5" bare copper wire
5" bare iron wire
Pencil
Candle

3. Cross the copper and iron wires together about 2" from one end.

4. Twist the wires together for the remainder of their lengths.

5. Wrap the twisted wires around a pencil to compress. Remove the pencil.

6. Connect the copper wire to the positive terminal of the multitester, and the iron wire to the negative terminal.

7. Light the candle and heat the twisted section of the wire.

8. Record what happens to the meter reading.

_________________________________________________________________

9. What conclusions can you draw from the results of your experiment?

_________________________________________________________________

10. Clean up your area and materials; set up to start the exercise over so that you can present it to the class.

11. At the appropriate time, you will be asked to demonstrate your experiment for the class. When you have finished, it is your responsibility to clean up and put away the materials you used.

AGRISCIENCE EXERCISE

- What is Electricity? Generating an Electromotive Force -

Student Data/Instruction Sheet

Group 4: EMF by Solar Radiation

Procedures:

1. As a group, read the entire experiment before proceeding further.

2. Gather all necessary materials for the experiment, as listed below:

Multitester
Test leads with alligator clips on both ends
Solar cell
Strong light source

3. Connect the solar cell to the multitester.

4. Bring a strong light source to the solar cell.

5. Record the meter reading: ____________________________________________

6. Does the meter reading indicate a higher or lower emf when the light source is brought near the solar cell? Why do you think this is true?

__________________________________________________________________

7. Place different colors of plastic film between the solar cell and the light source; record the meter readings for each color.

Color Meter Reading

_____________ _____________

8. Which color resulted in the highest meter reading? ________________________

Which resulted in the lowest reading? ___________________________________

What do you think accounts for the differences between readings for the colors you tried?

__________________________________________________________________

9. What conclusions can you draw from the results of your experiment?

_________________________________________________________________

10. Clean up your area and materials; set up to start the exercise over so that you can present it to the class.

11. At the appropriate time, you will be asked to demonstrate your experiment for the class. When you have finished, it is your responsibility to clean up and put away the materials you used.

TEACHER BACKGROUND SHEET

- What is Electricity? Generating an Electromotive Force -

The agricultural industry requires massive amounts of energy to operate. Petroleum-based fuels provide energy to operate machinery; the sun's energy is needed for plants to carry out photosynthesis; electrical energy is employed in lighting, heating, and cooling buildings, as well as many other jobs using electric motors.

Agriculture was transformed during the 1930's, with the introduction of electricity into America's rural communities. Electricity is a labor-saving device, which led to the replacement of hand cranks for starting tractors, as well as many other tasks which were once accomplished by manual labor. Electricity is considered an essential component of today's agricultural industry.

Electromotive force causes the movement of electrons through a conductor; this is abbreviated emf. Voltage and emf are interchangeable terms, meaning essentially the same thing. An emf may be generated in several different ways.

An electromotive force may be generated by two dissimilar metals (such as copper and zinc) when they are in contact with an electrolytic solution. This solution may be salt water, a sal ammoniac solution, or even a weak solution of some acid (such as natural fruit juice). In this experiment, an emf is generated by using a copper nail and a galvanized nail (which is coated with zinc). The electrolytic solution is the juice of a citrus fruit, such as a grapefruit, orange, or lemon.

Magnetism is the most common commercial method of generating an electromotive force. A moving magnetic field is passed through a coil of wire, producing an emf. Examples of this type of generation include the alternator of your car and the large generators used to produce electricity for homes and businesses.

Other techniques for producing an emf include the use of applied heat to produce a thermocouple from two dissimilar metals, and the use of solar cells.

The following results may be anticipated for this activity:

EMF by Chemical Reaction: The copper electrode will be positive and the zinc negative. The solution of sal ammoniac with the carbon and zinc electrodes should generate a greater emf than either of the other two solutions.

EMF by Magnetism: The meter moves in a positive direction when the north end of the magnet is inserted into the coil. When the magnet is not moving inside the coil, the meter should show no deflection. As the magnet is pulled from the coil, the meter should resume a reading.

EMF by Heat: The voltage output for this type of emf generation is less than that produced by a chemical reaction.

EMF by Solar Radiation: The meter reading should increase as the light source is brought nearer to the solar cell.

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Cell Unit	Solution	Electrode Polarity	Voltage Output
Zinc Copper	Saltwater	Zinc: __________ Copper: _______
Zinc Copper	Citric Acid	Zinc: __________ Copper: ________