Main electronics resistor component topics:
Basic resistor component properties:
- Resistors limit electric current from a voltage source, such as a battery or breadboard power supply. As a result,the amount of current flowing through a resistor depends on the voltage across it, and its resistance in units called Ohms (symbol Ω). The relationship between the voltage across a fixed resistor and the current flowing through a fixed resistor is linear. The relationship between voltage (V), resistance (R) and current (I) is known as Ohms law with the formulas being V=IR, I=V/R and R=V/I.
- Resistors create heat (power) based on the voltage across it and the current flowing through it. It’s wattage rating (In units called Watts) must not be exceeded. in fact, it is best to remain below 1/2 of the resistor wattage rating (most through hole resistors are rated for 1/4W (0.250W)). Make sure the resistor you use can handle the wattage you subject it to! People drawing schematic diagrams for electronic circuits will usually note the wattage resistor that is needed if 1/4W is insufficient. If no wattage rating is given, then a 1/4W is probably safe to use.
- Sets voltages (voltage divider) in a circuit based on the power source voltage and electrical properties of the other components in the circuit.
List of primary resistor topics:
- Resistance – Current passed through resistor based on voltage across it (Ohms law I=V/R). 1000Ω (one thousand ohms) of resistance will pass 0.005 amps (5 milliamps) of current (I) when 5 volts is across it. 5V/1000Ω=0.005A. NOTE: voltage is applied across and current flows through a resistor.
- Tolerance – Percentage difference of actual resistance value a given resistor should be expected to vary from it’s rated (advertised) value due to production inaccuracies.
- Wattage (power) – Heat generated by resistance due to current passing through it from the voltage across it.
- Wattage rating – The absolute maximum power dissipation a certain resistive component can be expected to dissipate when surrounded by normal room temperature air. 1/4W is the most common though hole value.
- Fixed versus variable resistance – Most resistors provide a steady amount of resistance but some are made to provide a range of resistances due to outside influences such as manually controlled (potentiometer/trimpot), light (light dependent resistor LDR), temperature (thermistor), etc.
- Color code – Most through hole resistors have 4 or 5 colored stripes to indicate their rated value and tolerance. first 2 or 3 stripes give numerical values of the first 2 or 3 digits. The second to last stripe gives the multiplier. And, the final stripe gives the tolerance.
Reading the color code to find the value
Through hole (wires at each side) resistors have their resistance rating in Ohms indicated by colored stripes/bands. You simply hold the tolerance band (5% gold and 1% brown are common) to the right and read the bands starting from the left. For the 4 stripe beige resistors, the first band is the first digit. The second band is the second digit. The third band is the multiplier (number of zeros). And the final band is the tolerance (percentage of higher or lower error that is possible from it’s rated value). The blue resistors have 5 bands, first 3 are the digits, 4th is the multiplier and fifth is the tolerance.
Resistors commonly come in labeled packaging and can be measured by a multimeter. Therefore, don’t feel you have to memorize the code.
Equivalent resistance – Multiple resistors connected in series and/or parallel will act like a single resistor with the combined electrical properties of the individual resistors. Series = greater resistance and voltage division. Parallel = less resistance (greater conduction) and more surface area for heat dissipation.
Equivalent resistance:
Series resistors:
When you connect resistors end to end (in series) then the resistance simply adds up. This is known as the total resistance of the series resistors.
Rt = R1 + R2 …. (Resistance total equals resistor 1 plus resistors 2 and any other number of resistors)
Parallel resistors:
When you connect both ends of multiple resistors to each other as part of a circuit, they will all pass current independently of each other. The current that each resistor passes through it will add up with the other parallel resistors. Therefore there is more current for a given voltage (I = V/R) and a lower equivalent resistance when resistors are connected in parallel.
To be added: varistor
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