Resistor Photo:
Variable Resistor, Potetiometer or Trim Pot symbol:
The resistor is an electrical device that is used to limit and control the flow of electricity. Resitors are usually represented by the letter "R" in schematics. The "Ohm" is the unit of measure of resistance. Typical values: 0.1 ohm to 10 megohms. The higher the resistance value, the greater the resriction. A variable resistor can control the flow of current in a wire just as a valve controls the flow of water in a pipe.
Ohm's Law: V = I * R
Voltage (V) equals Current (I) times Resistance (R).Three variations of Ohm's Law: V = I*R I = V/R R = V/I
Definitions of electrical terms:
Voltage (V):
Voltage is a measure of electromotive force. The higher the voltage; the stronger the force. Voltage in a wire is like pressure in a water pipe.Current (I):
Current is a measure of flow of electricity. The higher the current; the greater the flow. Current in a wire is like the amount of water flowing in a water pipe.Resistance (R):
Resistance is a characteristic of an electrical component that restricts the flow of electricity. Resistance in a wire acts like a restriction in a water pipe. The higher the value, the higher the restriction. 1K ohm = 1000 ohms 1M ohm = 1000000 ohms.Measuring Resistance with a Digital Multimeter (DVM):
Set the DVM to "Ohms" or "Resistance" and touch the 2 leads from the meter to the 2 leads on the resistor to measure the resistance of the resistor. Try a variety of resistors of different values and note the different readings. Note that the meter never reads exactly the value stamped on the resistor. Resistors are not perfect and the meter is not perfect.
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Measuring Voltage with a Digital Multimeter (DVM):
Set the DVM to "Volts" and touch the DVM leads to the 2 battery terminals to verify that the battery is generating 9V.
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Measuring Current with a Digital Multimeter (DVM):
Connect the 2 terminals of a 10K resistor to the 2 terminals of the 9V battery. According to the formula I= V/R, 0.009 amps (or 9 ma) should be flowing through the resistor. Set the DVM to "Milliamps" and connect the DVM leads in series with the resistor leads. The DVM should display 9 ma.
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Voltage Divider:
Connect two 10K resistors in series across the terminals of a 9V battery as shown below. Measure the voltage across each resistor. The voltage across each resistor should be about 4.5 V. The sum of the voltages across each resistor should equal the battery voltage (9 V).
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