Introduction to Electronics

Physics Online 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. You will also do a simple test of Ohm’s law. 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.

Equipment You Procure  digital camera  AA battery

Equipment from Kits  2 digital multi-meters  battery holder  all resistors  styrofoam chunk  alligator clips

Experimental Procedures 1) Using the color-code chart provided on the last page, compute and record the theoretical resistance and error of each resistor. Convert the percentage error to an absolute error. 2) Use a digital multi-meter as an ohmmeter (see instructions on the last page) to measure and record the experimental resistance of each resistor. Include an explicit estimation of the error in the experimental resistance (see instructions on the last page). Compare the theoretical and experimental resistances. Do the resistors work as advertised? 3) Set the digital multi-meter to the 2 V DC setting. Measure the potential difference across your AA battery by placing the probes at opposite ends of the battery. Compare this potential difference to the theoretical value of 1.5 V. 4) Select a resistor of less than 1000 Ω. Use Ohm’s law to predict the current through this resistor, assuming that it is connected to the AA battery (include error propagation). 5) Create a circuit using as shown (except you will use a AA battery instead of a 9 V battery). Place the battery in its holder as your last step. Be very careful to use the DC ammeter correctly since it is very easy to blow a fuse (see instructions on last page). Your ammeter setting should be informed by your calculation based on Ohm’s law (the lowest possible setting that still exceeds your prediction). You may choose to take a photograph of your configuration without the battery connected and e-mail it to your instructor to check. 6) Measure and record the experimental potential difference and current. Include an estimation of the error for both the potential difference and current (see instructions on last page). Did the battery provide a consistent potential difference (connected to resistor and not)? Did Ohm’s law provide a correct prediction of current?

Figure 1: The digital multi-meter in the upper right corner is configured as an ammeter at the 20 mA setting. It reads 9.31 ± 0.02 mA or 0.00931 ± 0.00002 A. The digital multi-meter in the lower right corner is configured as a voltmeter at the 20 V setting. It reads 9.21 ± 0.02 V. Connect the battery last so that you can reduce the risk of damaging your ammeter. Resistor Color Codes Blac Yello Blu Viole Brown Red Orange Green Gray White k w e t 0 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, red, orange, gold” resistor would be 42000 Ω ± 5% or 42000 ± 2100 Ω

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 (definitely don’t have any batteries in O the circuit). 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 V setting. If the setting is 200m, then the potential difference will be measured in mV. If the setting is anything else, 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, A 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 to a battery or generator alone or connect an ammeter “in parallel” to a circuit element of interest. It might blow a fuse and will definitely not provide useful data. 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.

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