Physics Resistor
Resistor
A resistor is a passive twoterminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, bias active elements, and terminate transmission lines, among other uses. Highpower resistors that can dissipate many watts of electrical power as heat may be used in motor controls, power distribution systems, or as part of motor starters. Resistors are common elements of RL and RC circuits and can be used to build analog filter networks.
Resistor Construction
Resistors are typically made of a resistive element (such as carbon, metal, or ceramic) that is wrapped around a core of insulating material (such as plastic or ceramic). The ends of the resistive element are then connected to two metal terminals.
Resistor Power Ratings
Resistors have a power rating that specifies the maximum amount of power that they can dissipate without being damaged. The power rating of a resistor is determined by its physical size and the material used to make it.
Resistor Tolerance
Resistors have a tolerance that specifies the maximum amount by which their resistance value can deviate from the nominal value. The tolerance of a resistor is typically expressed as a percentage of the nominal value.
Resistor Temperature Coefficient
Resistors have a temperature coefficient that specifies the amount by which their resistance value changes with temperature. The temperature coefficient of a resistor is typically expressed in parts per million per degree Celsius (°C).
Resistors are essential components of electronic circuits. They are used to control the flow of current, divide voltage, bias active elements, and terminate transmission lines. Resistors are available in a wide variety of types, sizes, and power ratings.
S.I. Unit Of Resistor
The SI unit of resistance is the ohm, which is symbolized by the Greek letter omega (Ω). It is named after the German physicist Georg Simon Ohm, who discovered the relationship between current, voltage, and resistance in 1827.
Definition of the Ohm
The ohm is defined as the resistance of a conductor that allows a current of one ampere to flow when a voltage of one volt is applied across it. In other words, one ohm is the resistance that will cause a current of one ampere to flow when a voltage of one volt is applied.
Multiples and Submultiples of the Ohm
The ohm is the base unit of resistance, but there are also multiples and submultiples of the ohm that are used to express larger or smaller values of resistance. Some of the most common multiples and submultiples of the ohm include:
 Kiloohm (kΩ): 1,000 ohms
 Megaohm (MΩ): 1,000,000 ohms
 Gigaohm (GΩ): 1,000,000,000 ohms
 Milliohm (mΩ): 0.001 ohms
 Microohm (μΩ): 0.000001 ohms
 Nanoohm (nΩ): 0.000000001 ohms
Measuring Resistance
Resistance can be measured using a variety of instruments, including ohmmeters, multimeters, and ammeters. Ohmmeters are specifically designed to measure resistance, while multimeters and ammeters can be used to measure resistance as well as other electrical properties.
Types of Resistor
Resistors are passive electronic components that impede the flow of electric current by introducing resistance. They are used in a wide range of electronic circuits and devices to control the flow of current, divide voltage, and provide various other functions. Resistors come in various types, each with its own unique characteristics and applications. Here are some common types of resistors:
1. Carbon Composition Resistors:
 Made of a mixture of carbon particles and a ceramic binder.
 Low cost and widely used in older electronic devices.
 Have a relatively high tolerance (5% to 20%) and are not very precise.
 Not suitable for highprecision applications or where stability is critical.
2. Carbon Film Resistors:
 Made by depositing a thin film of carbon on an insulating substrate.
 More precise than carbon composition resistors, with a tolerance of around 1% to 5%.
 Offer better stability and are less affected by temperature changes.
 Commonly used in generalpurpose electronic circuits.
3. Metal Film Resistors:
 Made by depositing a thin film of metal (usually nichrome) on an insulating substrate.
 Highly precise, with a tolerance of around 0.1% to 1%.
 Offer excellent stability and are less sensitive to temperature variations.
 Widely used in highprecision electronic circuits and devices.
4. Wirewound Resistors:
 Made by winding a resistive wire around a ceramic or metal core.
 Can handle high power levels and are often used in power circuits.
 Have a higher tolerance (around 5% to 10%) compared to other types of resistors.
 Offer good stability and are less affected by temperature changes.
5. Ceramic Resistors:
 Made of a ceramic material with a high resistance.
 Small in size and can withstand high temperatures.
 Have a high tolerance (around 5% to 10%) and are not very precise.
 Commonly used in highfrequency circuits and as surfacemount components.
6. Variable Resistors (Potentiometers):
 Allow the resistance to be adjusted manually by rotating a knob or slider.
 Come in various forms, such as linear potentiometers, rotary potentiometers, and faders.
 Used for volume control, brightness adjustment, and other applications where variable resistance is required.
7. Thermistors:
 Resistors whose resistance changes with temperature.
 Used as temperature sensors, selfresetting fuses, and in temperature compensation circuits.
 Can be either positive temperature coefficient (PTC) or negative temperature coefficient (NTC) thermistors.
8. Photoresistors (LDRs):
 Resistors whose resistance changes when exposed to light.
 Used as light sensors, in automatic lighting systems, and for detecting the presence or absence of light.
9. Varistors (MOVs):
 Voltagedependent resistors that exhibit a nonlinear resistance characteristic.
 Used for voltage protection and surge suppression in electronic circuits.
10. Fuses:
 Resistors designed to break the circuit when the current exceeds a specified level, protecting the circuit from damage.
 Made of a lowmeltingpoint metal alloy that melts and breaks the circuit when the current becomes too high.
These are just a few examples of the many types of resistors available. Each type has its own unique properties and applications, and the choice of resistor for a particular circuit depends on the specific requirements and design considerations.
Working Principle of a Resistor
A resistor is a passive electronic component that impedes the flow of electric current by converting electrical energy into heat energy. It is a vital component in electronic circuits, used to control the flow of current, divide voltage, and provide bias to transistors. The working principle of a resistor is based on the concept of resistance, which is the opposition offered by a material to the flow of electric current.
Key Components of a Resistor

Resistive Element: The heart of a resistor is its resistive element, which is typically made of a material with high resistivity. Common materials used include carbon, metal alloys (such as nichrome), and semiconductors. The resistive element determines the amount of resistance offered by the resistor.

Terminals: Resistors have two terminals, which are metal leads connected to the resistive element. These terminals provide electrical connections to the resistor and allow it to be integrated into a circuit.

Insulating Material: The resistive element and terminals are encased in an insulating material, such as ceramic or plastic. This insulation prevents electrical contact between the resistive element and the external environment, ensuring safe and reliable operation.
How Does a Resistor Work?
When a voltage is applied across the terminals of a resistor, an electric current starts to flow through the resistive element. The resistive material opposes the flow of current, causing a voltage drop across the resistor. This voltage drop is directly proportional to the current flowing through the resistor, as described by Ohm’s law:
$$ V = I * R $$
Where:
 V represents the voltage drop across the resistor in volts (V).
 I represents the current flowing through the resistor in amperes (A).
 R represents the resistance of the resistor in ohms (Ω).
The resistance of a resistor is determined by several factors, including the material used, its length, and its crosssectional area. Longer and thinner resistive elements have higher resistance, while shorter and thicker elements have lower resistance.
Formula for Resistor
A resistor is a passive electronic component that impedes the flow of electric current by converting electrical energy into heat energy. The resistance of a resistor is measured in ohms (Ω).
Formula
The formula for calculating the resistance of a resistor is:
$$ R = V / I $$
Where:
 R is the resistance in ohms (Ω)
 V is the voltage in volts (V)
 I is the current in amperes (A)
Example
For example, if a resistor has a voltage of 12 volts and a current of 2 amperes, the resistance of the resistor is:
$$ R = 12 V / 2 A = 6 Ω $$
Power Dissipation
The power dissipated by a resistor is calculated using the following formula:
$$ P = I^2 * R $$
Where:
 P is the power in watts (W)
 I is the current in amperes (A)
 R is the resistance in ohms (Ω)
Example
For example, if a resistor has a current of 2 amperes and a resistance of 6 ohms, the power dissipated by the resistor is:
$$ P = 2 A^2 * 6 Ω = 24 W $$
The formula for calculating the resistance of a resistor is R = V / I. The power dissipated by a resistor is calculated using the formula $P = I^2 * R$.
Colour Coding of Resistors
Resistors are electronic components used to control the flow of current in a circuit. They are often colourcoded to indicate their resistance value. This makes it easy to identify the value of a resistor without having to measure it with a multimeter.
How to Read Resistor Colour Codes
Resistors are typically marked with four or five coloured bands. The first three bands indicate the resistance value, while the fourth band indicates the tolerance. The fifth band, if present, indicates the temperature coefficient.
The colours of the bands are read from left to right. The first band is the most significant digit, the second band is the second most significant digit, and the third band is the least significant digit.
For example, a resistor with the following colour bands would have a resistance value of 120 ohms:
 Brown (1)
 Red (2)
 Orange (0)
The fourth band, which is gold in this case, indicates a tolerance of 5%. This means that the actual resistance value of the resistor could be anywhere from 114 ohms to 126 ohms.
Resistor Colour Code Chart
The following table shows the colour code for resistors.
Colour  Digit 

Black  0 
Brown  1 
Red  2 
Orange  3 
Yellow  4 
Green  5 
Blue  6 
Violet  7 
Grey  8 
White  9 
Tolerance Colour Code
The following table shows the tolerance colour code for resistors.
Colour  Tolerance 

Silver  10% 
Gold  5% 
Red  2% 
Brown  1% 
Temperature Coefficient Colour Code
The following table shows the temperature coefficient colour code for resistors.
Colour  Temperature Coefficient 

Black  0 ppm/°C 
Brown  10 ppm/°C 
Red  15 ppm/°C 
Orange  25 ppm/°C 
Yellow  50 ppm/°C 
Green  100 ppm/°C 
Blue  200 ppm/°C 
Violet  300 ppm/°C 
Grey  400 ppm/°C 
White  500 ppm/°C 
Resistor colour coding is a simple and effective way to identify the resistance value of a resistor. By understanding the colour code, you can quickly and easily find the resistor you need for your project.
Tolerance in Resistors
Resistors are electronic components used to control the flow of current in a circuit. They are manufactured with a specific resistance value, but due to variations in the manufacturing process, the actual resistance of a resistor may differ from its nominal value. This difference is known as tolerance.
Tolerance Specifications
Resistors are typically manufactured with a tolerance of 5%, 10%, or 20%. This means that the actual resistance of a resistor can be up to 5%, 10%, or 20% higher or lower than its nominal value. For example, a 100ohm resistor with a 5% tolerance could have an actual resistance anywhere from 95 ohms to 105 ohms.
Tolerance Bands
The tolerance of a resistor is indicated by colored bands on the resistor body. The first two bands indicate the significant figures of the resistance value, and the third band indicates the multiplier. The fourth band, if present, indicates the tolerance.
The following table shows the color code for resistor tolerance:
Color  Tolerance 

Brown  1% 
Red  2% 
Green  5% 
Blue  10% 
Yellow  15% 
Orange  20% 
Tolerance and Circuit Design
The tolerance of a resistor must be taken into account when designing a circuit. If the tolerance is too high, it can cause the circuit to malfunction. For example, if a circuit requires a 100ohm resistor with a 20% tolerance, the actual resistance of the resistor could be anywhere from 80 ohms to 120 ohms. This could cause the circuit to draw too much or too little current, which could damage the components.
Resistor tolerance is an important factor to consider when designing a circuit. By understanding the tolerance of a resistor, you can ensure that the circuit will function properly.
Applications of Resistor
Resistors are passive electronic components that impede the flow of electric current by introducing resistance. They are used in a wide range of electronic circuits and devices, from simple voltage dividers to complex amplifiers and oscillators. Some of the common applications of resistors include:
1. Current Limiting
Resistors can be used to limit the amount of current that flows through a circuit. This is important for protecting sensitive components from damage due to excessive current. For example, a resistor can be placed in series with an LED to limit the current flow and prevent the LED from burning out.
2. Voltage Division
Resistors can be used to divide a voltage into multiple smaller voltages. This is useful for creating reference voltages or for biasing transistors. For example, a voltage divider can be used to create a 5V reference voltage from a 12V power supply.
3. Load Matching
Resistors can be used to match the impedance of a source to the impedance of a load. This is important for maximizing power transfer and minimizing reflections. For example, a resistor can be used to match the impedance of an antenna to the impedance of a transmission line.
4. Filtering
Resistors can be used to filter out unwanted frequencies from a signal. This is useful for removing noise and interference. For example, a resistor can be used to filter out the highfrequency components of a signal.
5. Timing
Resistors can be used to create timing circuits. This is useful for controlling the duration of pulses or the frequency of oscillations. For example, a resistor can be used to create a delay circuit or an oscillator.
6. Sensing
Resistors can be used to sense the presence or absence of a signal. This is useful for detecting events or for triggering alarms. For example, a resistor can be used to detect the presence of a liquid or the movement of an object.
7. Power Dissipation
Resistors can be used to dissipate power. This is useful for protecting sensitive components from damage due to overheating. For example, a resistor can be placed in series with a power transistor to dissipate the heat generated by the transistor.
Conclusion
Resistors are versatile electronic components that have a wide range of applications. They are essential for controlling current, voltage, and power in electronic circuits.
Difference between Resistor and Resistance
Resistor
 A resistor is a passive twoterminal electrical component that implements electrical resistance as a circuit element.
 Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits.
 In electronic circuits, resistors are used to limit current flow, to adjust signal levels, bias active elements, and terminate transmission lines, among other uses.
 Highpower resistors that can dissipate many watts of electrical power as heat may be used in motor controls, power distribution systems, or as part of motor starters.
 Resistors are common elements of RL and RC circuits and can be used to build analog filter networks.
 Resistors are also used in combination with other passive electronic components to build oscillator circuits.
Resistance
 Resistance is a measure of the opposition to the flow of electric current in a conductor.
 The resistance of a conductor is directly proportional to its length and inversely proportional to its crosssectional area.
 The resistance of a conductor also depends on the material it is made of.
 The SI unit of resistance is the ohm (Ω).
 One ohm is the resistance of a conductor that allows one ampere of current to flow when one volt is applied across it.
 The resistance of a conductor can be measured using an ohmmeter.
Key Differences
 A resistor is a physical component used in electronic circuits, while resistance is a property of materials that opposes the flow of electric current.
 The resistance of a resistor is a fixed value, while the resistance of a material can vary depending on factors such as temperature and applied voltage.
 Resistors are used to control the flow of current and voltage in electronic circuits, while resistance is a fundamental property of materials that affects the flow of electric current.
Resistor Materials
Resistors are passive electronic components that impede the flow of electric current by providing resistance. The resistance of a resistor is measured in ohms (Ω). Resistors are used in a wide variety of electronic circuits, including power supplies, amplifiers, and digital logic circuits.
The material used to make a resistor determines its resistance, temperature coefficient, and other electrical properties. Some of the most common resistor materials include:
Carbon Composition Resistors
Carbon composition resistors are made from a mixture of carbon powder, resin, and a filler material. They are the oldest type of resistor and are still widely used today due to their low cost and small size. Carbon composition resistors have a relatively high temperature coefficient, which means that their resistance changes significantly with temperature.
Metal Film Resistors
Metal film resistors are made from a thin layer of metal deposited on a ceramic substrate. They have a lower temperature coefficient than carbon composition resistors and are more stable over time. Metal film resistors are available in a wide range of resistances and are often used in precision electronic circuits.
Wirewound Resistors
Wirewound resistors are made from a coil of resistive wire wrapped around a ceramic or metal core. They have a very low temperature coefficient and are capable of handling high power levels. Wirewound resistors are often used in power supplies and other highpower circuits.
Other Resistor Materials
In addition to the three most common resistor materials listed above, there are a number of other materials that can be used to make resistors. These include:
 Cermet resistors: Cermet resistors are made from a mixture of ceramic and metal powders. They have a low temperature coefficient and are often used in precision electronic circuits.
 Thick film resistors: Thick film resistors are made from a thick layer of resistive material deposited on a ceramic substrate. They have a higher temperature coefficient than metal film resistors but are less expensive.
 Thin film resistors: Thin film resistors are made from a thin layer of resistive material deposited on a metal substrate. They have a lower temperature coefficient than thick film resistors but are more expensive.
The choice of resistor material depends on the specific application. Factors such as resistance, temperature coefficient, power handling capability, and cost must all be considered when selecting a resistor material.