By John Sanger
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If, on the one hand, you mean does high voltage always have high current and low voltage always have low current, then the answer is no. For example, your car's battery is 12VDC but it may be required to deliver several hundred amperes to start your car. The digital clockradio on your nightstand operates on 120VAC and probably con sumes less than one ampere. On the other hand, if you mean is there an arithmetic relationship between current and voltage, the answer is yes. The relationship be tween current, voltage, and resistance is called Ohm's law.
Tantalum capacitors are usually more expensive than electrolytic capacitors. 5 μΐ to 50 μ¥, and their working voltages rarely exceed 50 volts. VARIABLE CAPACITORS Most capacitors have fixed values, as do most resistors. Also, similar to resistors, some are available with variable values. The schematic symbol for a variable capacitor is shown in Figure 2 - 1 4 . DIODES A device that allows current to flow in one direction only is called a diode. The common schematic symbol for a diode is shown in Figure 2-15.
2V, 50mA LED 5V, DPDT relay 68-ohm, 10%, 1/2-watt resistor NO switch from initiating device N O switch from relay NC external reset switch 42 BASIC ALARM ELECTRONICS TROUBLESHOOTING WITH SCHEMATICS Understanding what components do, as well as where they are located in circuits, helps you find and correct problems. For example, a sche matic might show a 1,000-ohm resistor between two components. If you measure resistance and find it very high, it may indicate the resis tor is defective. If a flashlight is not working, a schematic will help you start your troubleshooting procedures.