Introduction to Electronics
Introduction
The purpose of this lab is to understand basic electronic measurements, components, and test equipment. The majority of electronic instrumentation is based on the concepts of current, potential difference, and resistance.
· Current (I) is the time rate of flow of charge through a device. The SI unit of current is the ampere (amp or A).
· Potential difference (ΔV, often abbreviated as V) is the electrical potential energy per unit charge. The SI unit of potential difference is the volt (V).
· Resistance (R) is the ratio of potential difference to current. The SI unit of resistance is the ohm (Ω).
Note on terminology: Distinguish between a quantity and its SI unit. Avoid referring to current as “amperage” and potential difference as “voltage”. Add these two terms to the list of banned expressions in lab reports.
Electrical components and test equipment can be connected together in either series or parallel configurations. Two components are “in series” if they are connected to each other end-to-end and no other component is connected to that junction. Two components are “in parallel” if they are connected at both ends.
In this lab, you will investigate some simple electronic circuits and components. At the end of this lab, you should be able to read the color code on a resistor and use a digital multi-meter to measure resistance, potential difference, and current. You will also do a simple test of Ohm’s law.
Experimental Procedures
1) Select five resistors at random. Do not spill the box of resistors. Using the color-code chart provided on the next page, compute and record the theoretical resistance (and error) of each resistor. Convert the percentage error to an absolute error.
2) Use the digital multi-meter as an ohmmeter (see instructions on the next page) to measure and record the experimental resistance (and error; be specific) of each resistor. Compare the theoretical and experimental values. Do the resistors work as advertised?
3) Select a 470 Ω resistor. Use the digital multi-meter as an ohmmeter to measure and record the resistance (and error; be specific) of the resistor.
4) Create a circuit using the power supply and the 470 Ω resistor. Using the digital multi-meter as a DC voltmeter capable of measuring up to 20 volts, measure and record the potential difference (and error; be specific) across the closed circuit (see instructions on the next page).
5) Divide the measured potential difference by the measured resistance to calculate a theoretical value for the current.
6) Unplug the power supply. Configure the digital multi-meter as a DC ammeter (see instructions on the next page). Insert the ammeter into the circuit and check your configuration with the instructor. Plug in the power supply once your configuration has been approved. Measure and record the current flowing in the circuit. Compare the experimental and theoretical values. Did Ohm’s law make a correct prediction?
Resistor Color Codes
Black / Brown / Red / Orange / Yellow / Green / Blue / Violet / Gray / White0 / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9
Find the “tolerance band” which specifies the manufacturer’s error estimation for the resistance. It will typically be red (±2%), gold (±5%), or silver (±10%) and slightly separated from the other bands. Starting from the opposite end, identify the first band and write down the number associated with that color. Identify the second band and write down the number associated with that color. Identify the third or “multiplier” band and write down that number of zeroes. For example, a “yellow, brown, orange, gold” resistor would be 41000 Ω +/- 5%.
Digital Multi-Meter as an Ohmmeter
The digital multi-meter should come with 2 cables. Plug the red one into the hole labeled “V/Ω”. Plug the black cable into the hole marked “COM”. Turn the dial to the region marked “OHM” and the setting that is the lowest possible and still above your expected resistance. Place the red lead and the black lead at opposite ends of a resistor or group of resistors that is not connected to anything else. The reading displayed will be the resistance in units as specified by the setting. If the setting is 200, then the resistance will be measured in Ω. If the setting is 2K, 20K, or 200K, then the resistance will be measured in kΩ. If the setting is 2M or 20M, then the resistance will be measured in MΩ.
Digital Multi-Meter as a Voltmeter
Place the cables in the same holes as with the ohmmeter. Turn the dial to the region marked “DCV” for DC circuits or “ACV” for AC circuits. Choose a setting that is the lowest possible and still above your expected potential difference. Place the leads at opposite ends of a circuit element or combination of elements and observe the potential difference or potential difference across the circuit element or combination of elements in units as specified by the setting. If the setting is 200m, then the potential difference will be measured in mV. If the setting is anything else, then the potential difference will be measured in V.
Digital Multi-Meter as an Ammeter
Please be careful using the digital multi-meter as an ammeter because it is a sensitive device. Plug the red cable into the hole labeled “A” or “mA”. Plug the black cable into the hole marked “COM”. Turn the dial to the region marked “DCA” for DC circuits or “ACA” for AC circuits. Place the ammeter “in series” with the circuit element you wish to measure current through. To place the ammeter “in series” with the circuit element, disconnect one connection to the circuit element, then connect one lead to the circuit element and connect the other lead to the point where the circuit element used to be connected. The ammeter should now measure the current in units as specified by the setting. If the ammeter setting is 200μ, then the current will be measured in μA. If the ammeter setting is 2m, 20m, or 200m, then the current will be measured in mA. If the current setting is 2, then the current will be measured in A.
Note: Never connect an ammeter “in parallel” to a circuit element of interest because it might blow a fuse and will definitely not measure the current through the circuit element. Please consult with your instructor if this is not clear.
Error with the Digital Multi-Meter
You may assume that the last digit displayed is ±2 unless you have evidence otherwise. These error estimations must be made specific to each measurement in your reports or you will not receive full credit.
Save this page for future use!