Resistor 

Resistor Definition: -

A resistor is an electronic component that resists the flow of electric current. It controls the amount of current flowing by providing resistance. Resistance is measured in ohms (Ω). The higher the resistance, the lower the current that can pass through.

Imagine it this way: if electricity is water flowing through a pipe, a resistor is like a narrow section of that pipe that limits how much water (current) can flow through.

Resistor Construction:-

Resistors are normally made of a resistive element (which includes carbon, metal, or ceramic) that is wrapped around the middle of insulating material. The ends of the resistive detail are then connected to 2 steel terminals. 

S.I. unit of resistor:-

The SI unit of resistance is the ohm, represented by the Greek letter omega (Ω). It's named after German physicist Georg Simon Ohm. 

How Does a Resistor Work:-

Every resistor has two terminals and is placed in a circuit to reduce or regulate current. When current passes through it, some of the electrical energy is converted into heat — this is why some resistors get warm during operation.

For instance, if an LED (light-emitting diode) is connected directly to a battery without a resistor, it might burn out due to too much current. A resistor is added in series with the LED to protect it by limiting the current.

Types of Resistors:-

Linear Resistors & Non-Linear Resistors, and Thermistors

Linear Resistors: -

• Fixed resistors
• Variable resistors.

Non-Linear Resistors and Thermistors: -

• Varistor Resistors.
• Photoresistor or LDR (light-dependent resistors)
• Surface-Mounted Resistors 

There are several types of resistors, each with specific uses:-

1. Fixed Resistors: These have a set resistance value (e.g., 220Ω, 1kΩ).

2. Variable Resistors (Potentiometers): These allow the resistance to be adjusted manually.

3. Thermistors: These change resistance with temperature.

4. LDRs (Light Dependent Resistors): These change resistance based on light intensity.

Working Principle of a Resistor:-

A resistor is a passive digital thing that impedes the go with the flow of electric current by converting electric power into heat energy. It is a vital issue in digital circuits, used to govern the flow of modern-day divided voltage and offer bias to transistors. The running principle of a resistor is based on the idea of resistance, that is, the opposition provided by using a cloth to the drift of electric cutting-edge.

How Does a Resistor Work:-

When a voltage is applied across the terminals of a resistor, an electric powered contemporary starts to flow through the resistive element. The resistive material opposes the go with the flow of cutting-edge, inflicting a voltage drop throughout the resistor. This voltage drop is without delay proportional to the current flowing through the resistor, as described by way of Ohm’s law:

V=I*R

Where:

• V represents the voltage drop throughout the resistor in volts (V).
• I represents the modern-day flowing through the resistor in amperes (A).
• R represents the resistance of the resistor in ohms (Ω). 

Where Do Resistors Get Used:-

In electronics, resistors are ubiquitous:

• To regulate voltage levels in power supplies

• To avoid burning out, in LED circuits

• To regulate sound signals in audio devices

•  In sensors, televisions, fans, and numerous other devices

They are employed in signal filtering, voltage division, current limitation, and biasing active components (such as transistors).

Colour Bands Explained in the Resistor Colour Code Chart:-

Resistors often come with coloured bands printed on them — this is called the resistor colour code. It assists you in determining the temperature coefficient, resistance value, tolerance, and occasionally reliability.

*Advice to Keep in Mind:-

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  → Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White
• Gold and silver never come first — they’re only used in multiplier or tolerance bands.

 

Colour	Digit	Multiplier	Tolerance
Black	0	1 (10⁰)	—
Brown	1	10 (10¹)	±1%
Red	2	100 (10²)	±2%
Orange	3	1,000 (10³)	—
Yellow	4	10,000 (10⁴)	—
Green	5	100,000 (10⁵)	±0.5%
Blue	6	1,000,000 (10⁶)	±0.25%
Violet	7	10⁷	±0.1%
Gray	8	10⁸	±0.05%
White	9	10⁹	—
Gold	—	0.1 (10⁻¹)	±5%
Silver	—	0.01 (10⁻²)	±10%
No colour	—	—	±20%

 How to Interpret a 4-Band Resistor

The majority of resistors have four bands:

First Band: Initial digit
Second Band: The second number
Band 3: Multiplier
Band 4: Tolerance

Example 1: Red – Violet – Orange – Gold

• 1st digit: Red = 2
• 2nd digit: Violet = 7
• Multiplier: Orange = 1,000
• Tolerance: Gold = ±5%

Resistance = 27 × 1,000 = 27,000Ω or 27kΩ ±5%

what is an SMD resistor:-

Instead of utilising conventional through-hole technology, an SMD resistor is a small, rectangular resistor that is intended to be mounted directly on the printed circuit board (PCB).

SMD resistors are utilised in small, contemporary electronics such as

• Cell phones
• Computers
• LED light bulbs
• Smartwatches
• Medical equipment

Size of SMD Resistors:-

SMD resistors are available in the following standard sizes:

Code	Size (mm)
0201	0.6 × 0.3 mm
0402	1.0 × 0.5 mm
0603	1.6 × 0.8 mm
0805	2.0 × 1.25 mm
1206	3.2 × 1.6 mm

 

How to Read an SMD Resistor Code:-

SMD resistors use a 3-digit or 4-digit numeric code:

 3-digit code (like 472)

First two digits: significant numbers

Third digit: multiplier (power of 10)

Example:
472 = 47 × 10² = 4700Ω or 4.7kΩ

 

4-digit code (like 1001)

First three digits: significant numbers

Fourth digit: multiplier

Example:
1001 = 100 × 10¹ = 1000Ω or 1kΩ

 

Benefits of SMD Resistors:-

•  Extremely small and light
• Ideal for automated PCB assembly
• Utilised in circuits with high frequencies
• Reduced expenses in large-scale manufacturing

 

Disadvantages of SMD Resistors:-

• Soldering by hand is challenging.
• Values are more difficult to read.
• Lower power consumption in contrast to through-hole resistors