Learn Electronics/Resistors

Voltage Drop

 * Think of a bucket full of water; nothing happens yet, if there is no hole at the bottom of the bucket. The height of the water in the bucket represents the electrical voltage.
 * If there is a hole at the bottom of the bucket, then water will flow out of it. That water flow represents electric current flow.
 * If the source of the voltage is a battery, then, in time, the battery's voltage will be reduced until there is no voltage left, just as the level of the water in the bucket will get lower and lower until no water is left in the bucket, with zero level.
 * If the source of the voltage is the socket in the wall, then the voltage will remain about the same; normally there will be only slight changes of that kind of voltage.

The voltage is the source of the current, and the current has some purpose, it flows through what is called a "load", which may be one or more resistors. No current flows through a resistor or equivalent, unless there is a voltage across the two terminals of the resistor. If there are at least 2 resistors, or equivalent, in series (like a river flowing via 3 points) then the voltage across each resistor is called voltage drop. Think of a river passing via points A, B, and C, where A is highest and C is lowest. There is a difference in the elevations/levels, with B minus A representing a voltage drop, and C minus B being like another voltage drop. The sum of all of the voltage drops in a circuit always equals the supply voltage, such as the battery voltage.

Ohms Law
Resistors: Resistors "resist" the flow of electricity, reducing the amount of the current (measured in units called amps). Without a resistor in the circuit the current would be too high, you would ruin parts of the circuit, use up the battery too fast, or even blow the battery. Since resistors are too small to print numbers on them they are labeled with color coded bands that have to be interpreted. Resistors have 3 or 4 colorbands on them, but only the first 3 matter for now. The fourth one is either silver or gold. Silver means it is 10% above or below the value shown by the first 3 bands, while gold means 5% above or below. The first 2 bands represent a one decimal number, the third represents the number of zeros that follow.

Resistors follow Ohm's Law: $$V=IR$$ (V=Voltage, I=Current (in amps), R=Resistance (in ohms))

Ohm's law is important to remember since most electronic components have a maximum and minimum voltage and amp rating: if they're too low it wouldn't work, and if they're too high it will destroy the component. As long as you have at least two values you can solve for the last one.

Colour Code


The Standard EIA Color Code Table per EIA-RS-279 is shown on table as followed : A trick to remember is that the decimal number of a color band is equal to the amount of zeros added to the end if it's the third band.

Series & Parallel
Resistors are very useful in electronic design and there are 2 types of resistor connection mainly series and parallel.

Series
Definition of series connection: Resistor is connected end-to-end in a line to form a single path through which current can flow.

Resistors in series are summed up as shown to obtain the total resistance of their combination.

$$ R = R_{1} + R_{2} $$

Parallel
Definition of parallel connection: The same wire is connected to one end of all the parts in parallel and another wire is connected to the other end of all the parts in parallel.

Resistors in parallel are the reciprocal (means: one divided by) of the total resistance of the combination of two resistors R1 and R2

$$ R = \frac{1}{R_{1}} + \frac{1}{R_{2}} $$

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