RESISTOR:
Ohm's law states that the voltage (V) across a resistor is proportional
to the current (I), where the constant of proportionality is the resistance
(R).
Equivalently, Ohm's law can be stated:
This formulation states
that the current (I) is proportional to the voltage (V) and inversely
proportional to the resistance (R). This is directly used in practical
computations.
Colour coding of resistors:
Carbon-composition
and carbon film resistors are too small to have the resistance value printed on
their housings. Therefore, bands of color are used to represent the resistance
value.
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The
first and second band represents the numerical value of the resistor, and the
color of the third band specifies the power-of-ten multiplier. The color
bands are always read from left to right starting with the side that has a
band closer to the edge.
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For
carbon-composition and carbon film resistors, the common tolerances are 5%,
10%, and 20%, indicating that the actual value of the resistor can vary from
the nominal value by ±5%, ±10% and ±20%. If the band is gold, it specifies a
5% tolerance; silver specifies a 10% tolerance; if no band is present, the
tolerance is 20%.
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Note
that the color-code system for capacitors is very similar to that of
resistors except there is a fifth band representing the temperature
coefficient. This band is the first one closest to one end of the capacitor.
The other four fall into the same order as mentioned for resistors. In this
case, the second, third, and fourth bands are used to determine the
capacitance. The fifth band represents the tolerance of the capacitor.
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