ENGR - Lab 1 Basic Measurement Concepts and Practices DC...

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Lab 1 21 Basic Measurement Concepts and Practices DC Voltage and Current Summary About 450 B.C. the Greeks discovered that if you rubbed amber with a piece of fur, the amber would attract lightweight particles. Since the Greek word for amber is elektron , this process ultimately became known as electrification and was perhaps the first example of electrical engineering and the ori- gin of the word "electron". The appendix contains some interesting pictures of insects and small reptiles trapped in ancient amber. A very large number of important electrical phenomena and engineering applications are based on the movement and/or control of electrons. Virtually all modern experimental methods depend on elec- tronic devices in one way or another. Therefore it is important to be able to measure moving or accumu- lated electric charges and their effects (current and voltage) in a quantitative manner. This experiment focuses on two inexpensive and versatile devices, a digital multimeter (DMM) and an analog volt-ohm meter (VOM), which are used extensively in measuring voltage and current. Educational Objectives After performing this experiment, students should be able to: 1. Operate a digital multimeter (DMM) in the DC voltage and current modes. 2. Operate a VOM in the DC voltage and current modes. 3. Measure voltages in various DC circuits. 4. Measure currents in various DC circuits. 5. Measure the potential differences between terminals of a variety of batteries. 6. Measure the voltage change in a thermocouple when temperature varies. 7. Measure the voltage change in a photodetector when a light source varies. 8. Solve the "lemon battery" problem. “To be acceptable as scientific knowledge a truth must be a deduction from other truths.” - Aristotle
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22 Background Information The two fundamental electrical measurements are potential difference (or voltage) and current. The nature of each quantity determines the method used for measurement. Different measurements affect the placement of each type of meter in the electrical circuit. This experiment begins with potential differ- ence or voltage measurements in simple two terminal systems. Potential difference is measured in volts. It is a measurement of the difference in the electrical potential between any two objects. In an electrical circuit, a voltmeter is used to measure the potential difference and must be placed across (in parallel with) the element(s) developing the voltage. (See Figure 1) Figure 1: Voltmeter placement to test voltage on Element 2. Current is measured in amperes or simply amps. It is the number of electrons that pass through a point in a given time. Standard electrical theory predicts that electrons tend to flow from a negative to a positive potential. In an electric circuit, an ammeter is used to measure this flow by making the ammeter part of the circuit (connecting the meter in series) and forcing the electrons to flow through the ammeter as shown in Figure 2. Voltmeter
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ENGR - Lab 1 Basic Measurement Concepts and Practices DC...

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