Know Current Electricity | Part 3 | Definitions, Formulas,etc

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Know Current Electricity Part 2

Colour code for resistors

       Resistor is an important component of electric circuits. We use to limit the current through a particular path of the circuit. Resistance available in the market are mainly of two types:

1)Wire wound resistors
2)Carbon resistors

    Carbon resistors

       This resistors are highly range resistors. They are small and inexpensive. Since they are small in size, their values are colour coded to mark their values in ohms. 

The value of R is printed in the form of colour rings. On one side there is tolerance ring (either golden or silver) start observing from the other side. First, two colour rings give first two digits of value and the 3rd ring indicates the decimal multiplier. In case tolerance ring is absent the colour of the ring lie closer to one terminal yhen start observing from that side.

Example If the code for the resistor is -

Orange white red golden, then its resistance

    ↓            ↓       ↓       ↓

    3            9  ✖️ 10²    5%, Ohm

Or     3900 ± 5%

         3.9  K ±  5%

   Wire wound resistors 

A wire wound resistor is an electrical passive component that limits current. The resistive element exists out of an insulated metallic wire that is winded around a core of non-conductive material. They can be produced very accurately, and have excellent properties for low resistance values and high power ratings.

Resistances in series and in parallel 

1) Resistance in series:- When a number of resistors are connected in series then the current flowing through each of them will be same.

If R1, R2, R3, be the three resistors connected in series then their equivalent resistance (Rs) is given by 

                                           Rs = R1 + R2 + R3

        Hence, when a number of resistors are connected in series, the equivalent resistance is equal to the sum of individual resistance. For 'n' resistors

                                        Rs = R1 + R2 + .....................+ Rn

2)Resistance in parallel:- When the number of resistors are connected in parallel, then the potential difference across each of them will be same. 

If 'n' resistors R1, R2, ......., Rn are connected in parallel, the equivalent resistance is given by

                                        1 =   1  +  1  +    1    ........... + 1 

                                       Rp     R1      R2      R3               Rn

Note- Hence when a number of resistances are connected in parallel, the reciprocal of the equivalent resistance is equal to the sum of reciprocal of individual resistance.