Phys 1801 Lab 1 SU
Lab 1W – Introduction to DC Circuits
INTRODUCTION
1. Objectives
In this lab, students will:
• learn how to use a digital multi-meter to measure voltage, current, and resistance;
• learn how to use breadboards to build simple electrical circuits;
• learn how to use a power supply;
• learn how to use a colour code chart to determine values of commercial resistors;
• Distinguish between linear and non-linear resistors
2. Apparatus
Digital multi-meter, power supply, breadboard, electric bulb, resistors, wires.
3. Reading
Serway and Jewett, Physics for Scientists and Engineers, tenth ed. Sections 26.1, 26.2, 27.1, 27.2
and 27.3, Section 10.4 Electrical Measuring Instruments, from OpenStax-UniversityPhysics2-
10.4
DC CIRCUITS
Ohm’s Law
An electric current is the flow of electric charges. In this lab you will deal with a direct current
(abbreviated DC), which flows always in the same direction. The current that continually
reverses its direction, called alternating current (abbreviated AC), will be studied later this term.
Circuit elements that offer resistance to current are called resistors. According to Ohm's law,
current (𝐼) that flows through resistance (𝑅) causes an electric potential difference, 𝛥𝑉, across
the resistor.
∆𝑉 = 𝐼𝑅 (1)
Measuring Current, Voltage and Resistance
The instrument used to measure current is called an ammeter. It must be connected in series with
the element through which current is measured. Only then does the charge that flows through the
element also flow through the ammeter. The internal resistance of the ammeter is very low, so
that only a very tiny voltage drop occurs across the ammeter. CAUTION: Always turn off the
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, Phys 1801 Lab 1 SU
power supply when connecting and disconnecting the ammeter to a circuit.
A voltmeter is an instrument used to measure voltage across an element in a circuit. The
voltmeter must be connected in parallel with the given element. This ensures that the voltage
drop across the voltmeter is the same as that across the given circuit element. The internal
resistance of the voltmeter is very large, so that very little current passes through it.
When using an ammeter or a voltmeter in DC circuits it is important to pay attention to the
polarity of the instruments. The positive (+) side of the voltmeter and the ammeter must be
closest to the positive (+) side of the battery.
An ohmmeter is an instrument used to measure the resistance of an element in a circuit. When
measuring the resistance of an element in a circuit, such as a resistor, it must be disconnected
from the circuit to ensure only the resistance due to the element in question is contributing to the
measurement.
To measure current, voltage or resistance you will use a modern instrument called a digital multi-
meter (DMM). “Multi” refers to the fact that the meter can serve as either a voltmeter, ammeter,
or ohmmeter. A rotary switch enables one to select the appropriate mode of operation and scale.
For example, if the rotary switch is set to 2 V DC as shown in Figure 1, the maximum voltage
reading is 2 V. To measure voltages up to 20 V, the rotary switch must be adjusted to the 20 V
DC setting. The cables must also be connected to the appropriate connection sockets for the
different meter settings as shown in Figure 1.
Figure 1: Digital Multimeter (DMM) settings. Note the position of the rotary switch and cable
connections for the different meter selections.
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Lab 1W – Introduction to DC Circuits
INTRODUCTION
1. Objectives
In this lab, students will:
• learn how to use a digital multi-meter to measure voltage, current, and resistance;
• learn how to use breadboards to build simple electrical circuits;
• learn how to use a power supply;
• learn how to use a colour code chart to determine values of commercial resistors;
• Distinguish between linear and non-linear resistors
2. Apparatus
Digital multi-meter, power supply, breadboard, electric bulb, resistors, wires.
3. Reading
Serway and Jewett, Physics for Scientists and Engineers, tenth ed. Sections 26.1, 26.2, 27.1, 27.2
and 27.3, Section 10.4 Electrical Measuring Instruments, from OpenStax-UniversityPhysics2-
10.4
DC CIRCUITS
Ohm’s Law
An electric current is the flow of electric charges. In this lab you will deal with a direct current
(abbreviated DC), which flows always in the same direction. The current that continually
reverses its direction, called alternating current (abbreviated AC), will be studied later this term.
Circuit elements that offer resistance to current are called resistors. According to Ohm's law,
current (𝐼) that flows through resistance (𝑅) causes an electric potential difference, 𝛥𝑉, across
the resistor.
∆𝑉 = 𝐼𝑅 (1)
Measuring Current, Voltage and Resistance
The instrument used to measure current is called an ammeter. It must be connected in series with
the element through which current is measured. Only then does the charge that flows through the
element also flow through the ammeter. The internal resistance of the ammeter is very low, so
that only a very tiny voltage drop occurs across the ammeter. CAUTION: Always turn off the
Page 1 of 13
, Phys 1801 Lab 1 SU
power supply when connecting and disconnecting the ammeter to a circuit.
A voltmeter is an instrument used to measure voltage across an element in a circuit. The
voltmeter must be connected in parallel with the given element. This ensures that the voltage
drop across the voltmeter is the same as that across the given circuit element. The internal
resistance of the voltmeter is very large, so that very little current passes through it.
When using an ammeter or a voltmeter in DC circuits it is important to pay attention to the
polarity of the instruments. The positive (+) side of the voltmeter and the ammeter must be
closest to the positive (+) side of the battery.
An ohmmeter is an instrument used to measure the resistance of an element in a circuit. When
measuring the resistance of an element in a circuit, such as a resistor, it must be disconnected
from the circuit to ensure only the resistance due to the element in question is contributing to the
measurement.
To measure current, voltage or resistance you will use a modern instrument called a digital multi-
meter (DMM). “Multi” refers to the fact that the meter can serve as either a voltmeter, ammeter,
or ohmmeter. A rotary switch enables one to select the appropriate mode of operation and scale.
For example, if the rotary switch is set to 2 V DC as shown in Figure 1, the maximum voltage
reading is 2 V. To measure voltages up to 20 V, the rotary switch must be adjusted to the 20 V
DC setting. The cables must also be connected to the appropriate connection sockets for the
different meter settings as shown in Figure 1.
Figure 1: Digital Multimeter (DMM) settings. Note the position of the rotary switch and cable
connections for the different meter selections.
Page 2 of 13
