Lab 02 - Resistance, Ohm's Law and Power
Thursday, 12 July 2018
8:33 AM
Introduction
Resistance is the opposition a substance offers to electrical current. The unit for resistance is the ohm, symbolized with the Greek letter capital omega (Ω). A resistor is a component designed to have a specific resistance and wattage rating. Resistors limit current, but in doing so, produce heat. The physical size of a resistor is related to its ability to dissipate heat, not to its resistance. A physically large resistor can dissipate more heat than a small resistor, hence the larger one would have a higher wattage rating than the smaller one.
Resistors are either fixed (constant resistance) or variable. Fixed resistors are usually color coded with a four-band or five-band code that indicates the specific resistance and tolerance. Each color stands for a number, as described in the Topic Notes and reprinted in Figure 2-1 for convenience.
The resistance of resistors is measured using a DMM. If you are using a nonautoranging DMM, a suitable range needs to be selected. 
Resistance normally should not be measured in a circuit as other resistors in the circuit will affect the reading. The resistor to be measured is removed from the circuit, and the test leads are connected across the resistance. The resistor under test should not be held between the fingers as body resistance can affect the reading, particularly with high-value resistors. (It is okay to hold one end of the resistor under test.)
The flow of electrical charge in a circuit is called current. Current is measured in units of amperes, or amps for short. The ampere is defined as one coulomb of charge moving past a cross-section of the conducting device in one second. Current is symbolized by the letter I (for Intensity) and is frequently shown with an arrow to indicate the direction of charge flow. Conventional current is defined as the direction a positive charge would move under the influence of an electric field. When electrons move, the direction is opposite to the direction defined for conventional current. To clarify the difference, the term electron flow is frequently applied to current in the opposite direction of conventional current flow.
Objectives
Determine the listed value of a resistor using the resistor color code.

Use the DMM to measure the value of a resistor.

Determine the percent difference between the measured and listed values of a resistor.
Measure the resistance of a potentiometer and explain its operation.
Measure the current-voltage curve for a resistor.
Construct a graph of data.
Given a graph of current-voltage for a resistor, determine its resistance.
Determine the power in a variable resistor at various settings of resistance.
Plot data for power as a function of resistance. From the plot, determine when maximum power is delivered to the variable resistor.
Equipment
1 Programmable DC Power Supply - Siglent SPD3303C
1 Digital Multimeter - Siglent  SDM3045X
Resistors – various

Breadboard, Hook-up wire

4mm leads (assorted colours), 2 BNC to 4mm leads
Safety
This is a Category A laboratory experiment. Please adhere to the Category A safety guidelines (issued separately).