University of Arkansas - AgriScience Project

AGRISCIENCE EXERCISE

PHYSICAL SCIENCES IN AGRICULTURE

Sub-Concept: Voltage, Amperage, and Resistance

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

Exercise: Measuring Electromotive Force (EMF)

Applied Principle(s): Force in electrical systems

Goals:

1. Define electromotive force.
2. Safely measure AC and DC voltages using analog and digital meters.
3. Predict total voltages for various battery connections.

Materials:

• Assortment of 6 and 9-volt batteries
• Connecting wires with alligator clips
• Digital and analog voltmeters
• GFCI-protected AC receptacle
• Safety eyewear

References: Refer to any basic electricity textbook for further information

Teacher Preparation Notes:

• This activity is an extension of the "Measuring Voltage, Amperage, and Resistance" exercise, and provides more in-depth practice in measuring electrical force.

Procedures for Conducting the Activity:

2. Instruct the students to complete the activity as directed on their data sheets. You may wish to monitor their progress as they work; however, it is suggested that the students be left to follow the instructions and complete the activity on their own.

3. Once all groups have completed the exercise, discuss the answers to the discussion questions as a class. Be sure to make note of the practical agricultural applications of the principles demonstrated.

AGRISCIENCE EXERCISE

- Measuring Electromotive Force (EMF) -

Student Data/Instruction Sheet

2. During this laboratory activity, you will rotate through several stations. The instructions for each station are presented below. Complete each station as directed by your instructor.

STATION 1

Determine the voltage of each battery using the analog meter and the digital meter. Record you meter settings, connections, and readings in the appropriate blanks below.

Battery	Setting (Scale)	Connections (Red and Black)	Reading (Analog/Digital)
A
B
C

STATION 2

Under your instructor's supervision, determine the voltage at the GFCI-protected receptacle. Record your meter reading below.

Receptacle Voltage: ____________________

STATION 3

Measure the voltage of each battery. Record the voltages below.

Battery	Voltage
A
B

Use the wires to connect the batteries in parallel ("+" to "+" and "-" to "-"). Measure the voltage of the combined batteries, and record your meter reading below.

Total Voltage in Parallel: __________________

Use one wire to connect the batteries in series ("+" of one battery to "-" of another). Measure the combined voltage of the batteries by placing meter leads across unused terminals. Record you meter reading below.

Total voltage in Series: _________________

STATION 4

Measure the voltage of each battery. Record the voltages below.

Battery	Voltage
A
B

Connect the two "+" battery terminals together using the wire. Attach the second wire to the "-" terminal of one battery. Attach the third wire to the "-" terminal of the other battery. Determine the voltage between the two wires attached to the "-" battery terminals. Record below.

Voltage across "-" terminals: _________________

STATION 5

Determine the voltage across the lamp fixture in this circuit. Record you reading below.

Voltage across lamp fixture: _________________

3. Complete the following discussion questions. Be prepared to share your answers in a class discussion.

a. Describe the correct meter connections required to determine DC voltage of a battery.

b. Describe the correct meter connections required to determine DC voltage of a lamp fixture.

c. Describe what happens when two batteries are connected in parallel. Where might this type of connection be used?

d. Describe what happens when two batteries are connected in series. Where might this type of connection be used?

e. Explain the meter readings you obtained at Station 4.

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