- Resistor resistance to the circuit and reduces the flow of electrical current.
- Reduce ? Depends on value of Resistor.
- These values are measured in ohms

**Ohm’s Law**

- V = voltage, I = current, R = resistance

- V= 12v, R = 600 Ohm

- I = 12 V/600 Ohm

- I = 0.02 A = 20 mA (milli Ampere)

- So the current in the circuit is 20 mA.

- R = 600 Ohm , I = 3 Ma

- V= 600 x 3 = 1.8 v

- Resistors have different wattage ratings (W = V X I)

- Quarter Watt , Half Watt, 1 Watt, 2 Watt etc.

**Tolerance of a Resistor**

Tolerance = value of resistor x value of tolerance band

Gold = ± 5%

Silver = ± 10 %

None = ± 20%

**Types of Resistor**

- Carbon
- Wire wound.
- Thin Film .
- Carbon Film.
- Metal Film.
- Thick Film.
- Metal Oxide .

**And then**

- Variable
- Fixed

**And then**

- NTC
- PTC

__Surface Mount Device__

The size of SMD resistors is indicated by a numerical code, such as 0603. This code contains the width and height of the package. So, the imperial code 0603 indicates a length of 0.060″ and a width of 0.030″

__Series Vs. Parallel__

Series = > R = r1+r2+r3+………rn

Parallel => 1/R = 1/r1 + 1/r2+…..1/rn

__Kirchhoff’s Laws__

The voltage around a loop equals the sum of every voltage drop in the same loop for any closed network and equals zero

**COLOUR CODE**

**5 Band Resistor Color Code**

**6 Band Resistor Color Code**

__Kirchhoff’s Voltage Law__

The algebraic sum of all voltages in a loop must equal zero.