types of Meters
An ammeter is used to measure current in a circuit. An ammeter (schematic symbol shown in Figure 15-4) can be considered a flow meter. It measures the number of electrons flowing past a given point in a circuit. The electrons must flow through the ammeter to obtain a reading as shown in Figure 15-5, and this is accomplished by opening the circuit and inserting the ammeter.
A voltmeter is used to measure the voltage (difference of potential) between two points in a circuit. A voltmeter can be considered a pressure gauge, used to measure the electrical pressure in a circuit (Figure 15-6).
Resistance is measured with an ohmmeter. To measure resistance, a voltage is placed across the device to be measured, inducing a current flow through the
device (Figure 15-7). When there is little resistance, a large current flows and the ohmmeter registers a low resistance. When there is great resistance, a small current flows and the ohmmeter registers a high resistance.
Questions
1. What is used to measure current?
2. What is used to measure voltage?
3. What meter is used to measure resistance?
4. Describe how to measure current with an ammeter.
5. Describe how to measure voltage with a voltmeter.
6. Describe how to measure resistance with an ohmmeter.