AGRISCIENCE EXERCISE
Physical Science in Agriculture
Teacher Guide
Key Concept:
Electricity and Electronic Systems
Sub-Concept:
Voltage, Amperage, and Resistance
Exercise:
Measuring Voltage, Amperage, and Resistance
Goals:
1. Safely and accurately measure voltage, amperage, and
resistance using analog and digital meters.
Applied Principle(s):
Measuring electrical quantities
Materials:
(per group)
Digital multi-meter
Wire bundles*
Fuses**
Battery sets***
Insulated conductors with clips
References:
Attached information sheet
Any basic electricity or physical science textbook
Teacher Preparation Notes/Conducting The Activity
It is suggested that the instructor set up each part of this activity for him/herself prior to
conducting the activity in class. This will aid in ansering students’ questions during the
activity.
* Wire Bundles: Prepare one per group by twisting together about six identical wires
into a bundle, so that the students will be unable to tell which ends belong to the same
wire without testing them. Label the wires on one end as “A”-“F”, and the other end as
“1”-“6”.
**Fuses: Each group of students should recieve a set of four fuses, some good and
some blown; they will have to determine which are which, so do not lable them.
***Battery Sets: Each group should receive a set of four batteries of different sizes.
1. Engage the class in a review discussion of the previous activity, “Generating an
Electromotive Force”.
Explain that today’s activity will involve methods of measuring electricity,
specifically voltage, amperage, and resistance.
2. Divide the class into small groups of no more than three students each.\
3. Provide each student with an information/data sheet, and allow the class time to
read the entire activity and information sheet.
4. Provide each group with the necessary materials for conducting the exercise.
5. Carefully supervise the groups as they work through the activity, providing
assistance as needed.
6. When all groups have completed their data sheets, review their answers as a
class, and discuss the practical applicatons of this information.
MEASURING VOLTAGE, AMPERAGE, AND RESISTANCE
INFORMATION SHEET
Measuring Voltage:
Voltage is the measure of electrical “pressure” which forces electricity
(electrons) to flow in a circuit. One volt is defined as the amount of electrical
pressure required to force one ampere of current to flow in a circuit having one
ohm of resistance. The higher the pressure (voltage), the greater the flow of
electrons (all other factors being equal). Common voltages in the US are 120V,
208V, and 240V. Industrical applications frequently use 480V electricity;
however, this is not common in most agricultural uses.
A voltmeter is used to determine circuit voltage. A direct current (DC)
voltmeter is used to measure voltage in DC circuits, while an alternating current
(AC) voltmeter is used to measure voltage in AC circuits. Meters which are used
to measure both AC and DC current are comonly available.
A voltmeter must always be connected between two wires, between a wire
and a ground, or across the terminals of an electrical device supplying or using
electricity. Typical voltmeter connections are illustrated below:
Measuring Amperage:
The ampere is the unit of measure of the rate of flow of electrons. When 6.28 X
flow past a given point in a circuit each second, one (1) ampere of
electicity is flowing in the circuit. A DC ammeter is used to meausre amperage in a DC
circuit; an AC ammeter is used to measure amperage in an AC circuit.
An ammeter must be placed in series in the circuit to measure amperage. This
means that the circuit must be opened and the ammeter must be wired into one current
carrying conductor of the circuit. It does not matter if the ammeter is installed in the
“hot” wire or the grounded wire of the circuit, since the same number of amperes flow in
both wires. The proper connection of an ammeter is illustrated below:
1018 electrons
A “clamp-on” ammeter can also be used to measure the amount of current
flowing through a wire. This type of meter is clamped around one of the current
carrying conductors. The meter measures the strength of the magnetic field produced
by the current flowing through the wire and converts this measurement to an amperage
reading. The clamp-on ammeter (illustrated below) is especially convenient, since its
use does not require that the ammeter be wired into the circuit.
Measuring Resistance:
When electrical current flows through a conductor, it encounters resistance. This
resistance to the flow of electricity is measured in ohms. The Greek capital letter
omega () is the symbol for ohms. For example, the number symbol combination “5”
means 5 ohms of resistance.
Resistance to the flow of electricity in a conductor is measured with an
ohmmeter. An ohmmeter conatins a battery that forces a small amount of current
through a conductor; the ohmmeter then measures the amount of resistance of the
conductor.
The conductor must be disconnected from the electrical power source prior to
measuring resistance. Failure to disconnect the conductor from the power source will
damage the ohmmeter.
An ohmmeter can be connected to a circuit in any place. It can be connected
either in series or parallel. The ohmmeter must be ‘zeroed’ out in order to make an
accurate reading. To zero out the meter, touch the two leads together and turn the
adjustment knob until the meter reads zero on the ohm scale.
Using a Volt-Ohm-Amp (VOA) Meter:
Single meters are now available which can measure voltage, resistance, and
amperage. These meters are commonly called VOA meters or multi-meters. They are
used in the same manner as described above, however the selector knob must be set
to select the type of meaurement desired (voltage, rsistance, or amperage).
As with any piece of equipment, always read the manufacturer’s instructions
prior to using any type of electrical meter. Failure to do so may result in personal injury
or damage to the meter.
Procedures for Conducting Activity/Data Sheet
1. Review the attached information sheet and read the remainder of the
exercise before proceeding further.
2. Obtain materials from your instructor:
*Digital multi-meter
*Wire bundle
*Battery set
*Fuse set
*Insulated conductors with clips
*Resistor
3. Determine the voltage (DC) of the four batteries and record below:
Battery A__________
Battery C__________
Battery B___________
Battery D___________
4. Connect Battery A and Battery B togehter in series; record the total voltage:
________________________.
5. Connect the same batteries together in parallel; record total voltage_______.
6. Based on your metter readings from steps 4 and 5, describe the effects of
connecting bateries in (s) series and (b) parallel:
(a)___________________________________________________________
_____________________________________________________________
_____________________________________________________________
(b)___________________________________________________________
_____________________________________________________________
_____________________________________________________________
7. Using the proper meter setting, determine which of the fuses are good and
which are “blown”, and record below:
Fuse A_________
Fuse C_________
Fuse B_________
Fuse D_________
8. Using the proper meter setting, identify both ends of each wire (e.g. B-5):
9. Measure and record amperage in the circuit as directed by your instructor:
__________________________
AGRISCIENCE EXERCISE
Physical Science in Agriculture
Student Guide
Key Concept:
Electricity and Electronic Systems
Sub-Concept:
Voltage, Amperage, and Resistance
Exercise:
Measuring Voltage, Amperage, and Resistance
Goals:
1. Safely and accurately measure voltage, amperage, and
resistance using analog and digital meters.
Applied Principle(s):
Measuring electrical quantities
Materials:
(per group)
Digital multi-meter
Wire bundles
Fuses
Battery sets
Insulated conductors with clips
References:
Attached information sheet
Any basic electricity or physical science textbook
MEASURING VOLTAGE, AMPERAGE, AND RESISTANCE
INFORMATION SHEET
Measuring Voltage:
Voltage is the measure of electrical “pressure” which forces electricity
(electrons) to flow in a circuit. One volt is defined as the amount of electrical
pressure required to force one ampere of current to flow in a circuit having one
ohm of resistance. The higher the pressure (voltage), the greater the flow of
electrons (all other factors being equal). Common voltages in the US are 120V,
208V, and 240V. Industrical applications frequently use 480V electricity;
however, this is not common in most agricultural uses.
A voltmeter is used to determine circuit voltage. A direct current (DC)
voltmeter is used to measure voltage in DC circuits, while an alternating current
(AC) voltmeter is used to measure voltage in AC circuits. Meters which are sued
to measure both AC and DC current are comonly available.
A voltmeter must always be connected between two wires, between a wire
and a ground, or across the terminals of an electrical device supplying or using
electricity. Typical voltmeter connections are illustrated below:
Measuring Amperage:
The ampere is the unit of measure of the rate of flow of electrons. When 6.28 X
1018 electrons flow past a given point in a circuit each second, one (1) ampere of
electicity is flowing in the circuit. A DC ammeter is used to meausre amperage in a DC
circuit; an AC ammeter is used to measure amperage in an AC circuit.
An ammeter must be placed in series in the circuit to measure amperage. This
means that the circuit must be opened and the ammeter must be wired into one current
carrying conductor of the circuit. It does not matter if the ammeter is installed in the
“hot” wire or the grounded wire of the circuit, since the same number of amperes flow in
both wires. The proper connection of an ammeter is illustrated below:
A “clamp-on” ammeter can also be used to measure the amount of current
flowing through a wire. This type of meter is clamped around one of the current
carrying conductors. The meter measures the strength of the magnetic field produced
by the current flowing through the wire and converts this measurement to an amperage
reading. The clamp-on ammeter (illustrated below) is especially convenient, since its
use does not require that the ammeter be wired into the circuit.
Measuring Resistance:
When electrical current flows through a conductor, it encounters resistance. This
resistance to the flow of electricity is measured in ohms. The Greek capital letter
omega () is the symbol for ohms. For example, the number symbol combination “5”
means 5 ohms of resistance.
Resistance to the flow of electricity in a conductor is measured with an
ohmmeter. An ohmmeter conatins a battery that forces a small amount of current
through a conductor; the ohmmeter then measures the amount of resistance of the
conductor.
The conductor must be disconnected from the electrical power source prior to
measuring resistance. Failure to disconnect the conductor from the power source will
damage the ohmmeter.
An ohmmeter can be connected to a circuit in any place. It can be connected
either in series or parallel. The ohmmeter must be ‘zeroed’ out in order to make an
accurate reading. To zero out the meter, touch the two leads together and turn the
adjustment knob until the meter reads zero on the ohm scale.
Using a Volt-Ohm-Amp (VOA) Meter:
Single meters are now available which can measure voltage, resistance, and
amperage. These meters are commonly called VOA meters or multi-meters. They are
used in the same manner as described above, however the selector knob must be set
to select the type of meaurement desired (voltage, rsistance, or amperage).
As with any piece of equipment, always read the manufacturer’s instructions
prior to using any type of electrical meter. Failure to do so may result in personal injury
or damage to the meter.
Procedures for Conducting Activity/Data Sheet
1. Review the attached information sheet and read the remainder of the
exercise before proceeding further.
2. Obtain materials from your instructor:
*Digital multi-meter
*Wire bundle
*Battery set
*Fuse set
*Insulated conductors with clips
*Resistor
3. Determine the voltage (DC) of the four batteries and record below:
Battery A__________
Battery C__________
Battery B___________
Battery D___________
4. Connect Battery A and Battery B togehter in series; record the total voltage:
________________________.
5. Connect the same batteries together in parallel; record total voltage_______.
6. Based on your metter readings from steps 4 and 5, describe the effects of
connecting bateries in (s) series and (b) parallel:
(a)___________________________________________________________
_____________________________________________________________
_____________________________________________________________
(b)___________________________________________________________
_____________________________________________________________
_____________________________________________________________
7. Using the proper meter setting, determine which of the fuses are good and
which are “blown”, and record below:
Fuse A_________
Fuse C_________
Fuse B_________
Fuse D_________
8. Using the proper meter setting, identify both ends of each wire (e.g. B-5):
9. Measure and record amperage in the circuit as directed by your instructor:
__________________________