Resistors are fundamental components used in electronic circuits to control the flow of electric current. They essentially do this by providing resistance, which is measured in units called ohms (Ω). The greater the resistance, the more it impedes or limits the flow of current.
Resistors work based on Ohm’s law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.
The formula for Ohm’s law is I=V/R, where I is the current in amperes, V is the voltage in volts, and R is the resistance in ohms.
Types of Resistors
There are many types of resistors, but the most common ones are fixed resistors and variable resistors.
- Fixed resistors have a resistance that cannot be changed. They come in many different resistance values to suit various applications. The resistance value is often indicated by color bands on the resistor body.
- Variable resistors, on the other hand, have a resistance value that can be adjusted. Potentiometers and rheostats are examples of variable resistors. Potentiometers are often used as volume controls in audio equipment, while rheostats are used in situations where it’s necessary to adjust the current flowing through a circuit.
Resistors are made from a variety of materials, including carbon, metal, and metal oxide films. The material, as well as the physical size of the resistor, can affect its power rating, or the amount of energy it can safely dissipate as heat.
Resistors are widely used in all sorts of electronic devices and circuits, including radios, televisions, and computers. They’re used to reduce current, divide voltages, adjust signal levels, terminate transmission lines, and much more.
What is a resistor?
A resistor is a fundamental component in electronics. The resistor is a passive device that introduces resistance into an electrical circuit to control or limit the flow of electric current. Resistors are often used in various applications like reducing current flow, adjusting signal levels, dividing voltages, bias active elements and terminating transmission lines, among others.
What is resistance in terms of electricity?
Resistance in terms of electricity is the opposition that a substance offers to the flow of electric current. It is a property that electric circuits exhibit to resist or limit the current flow.
The higher the resistance, the lower the current flow, given a certain applied voltage. The unit of resistance is the ohm (Ω).
What is Ohm’s Law?
Ohm’s Law is a fundamental principle in electronics that defines the relationship between voltage, current, and resistance.
Ohm’s law states that the current passing through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them. The formula is I = V/R, where I is current, V is voltage, and R is resistance.
What are the common types of resistors?
There are two primary types of resistors: fixed resistors and variable resistors. Fixed resistors have a predetermined resistance value that cannot be changed.
Examples include carbon-composition resistors and metal-oxide resistors. Variable resistors, on the other hand, have a resistance value that can be adjusted, like potentiometers and rheostats.
What are resistors made from?
Resistors are typically made from materials with moderate resistivity. They’re commonly made from carbon, metal, or metal oxide film. Other types, such as wire-wound resistors, are made from materials like nickel-chromium (Nichrome) wire.
What is a variable resistor and where is it used?
A variable resistor, also known as a rheostat or potentiometer, is a type of resistor whose resistance value can be adjusted. They are often used in applications where it’s necessary to adjust current, like in a light dimmer or volume control.
How is resistance measured?
Resistance is measured in units called ohms, symbolized by the Greek letter omega (Ω). The resistance can be measured using a multimeter or an ohmmeter.
What’s the difference between a resistor and a capacitor?
A resistor is an electronic component that resists the flow of electrical current, whereas a capacitor is a device that stores electrical energy in an electric field.
Resistors are often used for reducing current flow and voltage division, while capacitors are used in filtering, tuning circuits, and energy storage, among others.
How does temperature affect a resistor?
The resistance of most materials changes with temperature, a characteristic known as the temperature coefficient of resistance.
For some resistors like those made from metals, resistance increases with an increase in temperature. For others, like carbon or silicon, resistance decreases as temperature increases.
What is a pull-up resistor?
A pull-up resistor is used to ensure that a wire is pulled to a high logical level in the absence of an input signal. In other words, it’s a resistor used to pull the voltage level of a signal up to the desired level in a circuit. They’re often used in digital logic circuits to prevent undefined states.
How do resistors affect an LED?
LEDs (Light Emitting Diodes) require a specific voltage to operate and can be damaged by excessive current. A resistor in series with an LED is used to limit the amount of current that passes through the LED, ensuring that it can light up without being damaged.
What is a power resistor?
A power resistor is a type of resistor designed to handle and dissipate large amounts of power. They’re typically used in power generation systems and power distribution networks where they convert excess electrical energy into heat.
What does the color coding on a resistor mean?
The color coding on a resistor represents the resistance value of the resistor, along with its tolerance (accuracy). This system, called the Resistor Color Code, uses different colors to represent different numbers and multipliers.
For example, red represents the number ‘2’, orange represents ‘3’, and so on.
What is the function of a resistor in a circuit?
The function of a resistor in a circuit is to control the flow of electric current to other components. By creating a voltage drop, resistors can reduce current, protect components, divide voltages, and create known values of current and voltage.
What is the difference between a resistor and a transistor?
A resistor is a passive component used to resist the flow of current, while a transistor is an active component used to amplify or switch electronic signals. Transistors can control the output of current and voltage, while resistors simply reduce the current flow.
What is a shunt resistor?
A shunt resistor, also known as a current-shunt resistor, is a high-precision resistor used to measure electric current. By measuring the voltage drop across the shunt resistor, the current passing through can be calculated using Ohm’s law.
What is the role of a resistor in a voltage divider?
In a voltage divider circuit, two or more resistors are used in series to divide the input voltage into smaller voltages. The values of these resistors determine the division of the voltage.
What happens if a resistor fails or burns out?
If a resistor fails or burns out, it could disrupt the operation of the circuit, causing it to malfunction. Depending on the role of the resistor, the circuit could fail to operate, or operate incorrectly, or other components could be damaged by excessive current.
How do you calculate the total resistance of resistors in series?
For resistors in a series circuit, the total resistance (Rt) is simply the sum of all the resistances. The formula is Rt = R1 + R2 + R3 + … + Rn, where R1, R2, R3, … , Rn are the resistance values of the resistors.
How do you calculate the total resistance of resistors in parallel?
For resistors in a parallel circuit, the formula for total resistance (Rt) is 1/Rt = 1/R1 + 1/R2 + 1/R3 + … + 1/Rn. The reciprocal of the sum of the reciprocals of the individual resistances gives the total resistance.
What are SMD resistors?
A: SMD stands for Surface Mount Device, and an SMD resistor is a type of resistor that’s designed to be mounted on the surface of a circuit board, instead of being inserted into holes drilled in the board (like through-hole resistors).
They are typically smaller than traditional resistors and are widely used in modern electronics due to their size and ease of automation in the manufacturing process.
What’s the significance of the tolerance in a resistor?
The tolerance of a resistor indicates how much the actual resistance value of a resistor may deviate from its nominal value.
For example, a resistor with a nominal value of 100 ohms and a tolerance of ±5% could have an actual resistance value anywhere between 95 and 105 ohms. Tolerance is crucial in applications where precise resistance values are required.
What is a “decade resistor”?
A decade resistor is a type of instrument that contains resistors of different values that can be configured in a way to yield a large number of possible resistance values. This is typically used in lab settings for applications that require precise and variable resistance.
How does a resistor dissipate power?
A resistor dissipates power by converting electrical energy into heat. The power (P) dissipated by a resistor can be calculated using the formula P=I2R, where I is the current through the resistor and R is the resistance. The dissipated power is released in the form of heat.
What does “wattage rating” or “power rating” mean in a resistor?
The wattage or power rating of a resistor indicates the maximum amount of power that the resistor can safely dissipate as heat. If a resistor is used above its power rating, it can overheat and fail. The power rating is usually specified in watts (W).
What is a “zero-ohm resistor”?
A zero-ohm resistor is essentially a jumper wire that’s used to connect traces on a printed circuit board (PCB). While it’s called a “resistor”, it doesn’t actually provide any resistance. It’s often used in PCBs that are produced in an automated fashion, as it can be placed using the same equipment used for regular resistors.
What is the function of resistors in a filter circuit?
In a filter circuit, resistors are used in conjunction with capacitors or inductors to control the frequency response of the circuit. The values of the resistors, along with the other components, determine the frequencies that the filter passes or rejects.
What is a load resistor?
A load resistor is used to draw power from a source in a circuit, effectively acting as the “load” in the circuit. It can also be used to simulate a particular load in testing and development scenarios. In some cases, it’s used to ensure stable operation of certain circuits by providing a minimum level of power draw.
What does a “bleeder resistor” do?
A bleeder resistor is a safety device used in electrical systems to discharge capacitors when the power is turned off, preventing a potentially dangerous electrical shock if the capacitors were touched when charged. It’s called a “bleeder” resistor because it slowly “bleeds” off the charge.
What are “precision resistors”?
Precision resistors are resistors that are designed to have a very accurate and stable resistance value, often with very low tolerance values (like ±0.01%). They are used in circuits where high accuracy and stability are required, such as in measurement and calibration equipment.
How are resistors used in amplifier circuits?
Resistors play several key roles in amplifier circuits. They can be used in the feedback loop of an amplifier to control its gain, in the input and output stages to match impedance, and to bias transistors into their correct operating regions. The exact function of each resistor depends on the specific design of the amplifier.
What are thermistors?
Thermistors are a type of resistor whose resistance changes significantly with temperature. They come in two types:
NTC (Negative Temperature Coefficient), where resistance decreases as temperature increases, and PTC (Positive Temperature Coefficient), where resistance increases as temperature increases. They are often used in temperature sensing and control applications.
What is a “current limiting resistor”?
A current-limiting resistor is a resistor used in a circuit to limit the amount of current that can flow through a component or a circuit. They are often used to protect components that can be damaged by excessive current, such as LEDs.
What is a “pull-down resistor”?
A pull-down resistor is used to ensure a wire is at a low logical level when it’s not being actively driven to a high level. This prevents an input from floating when no active signal is being applied, which can lead to undefined or erroneous behavior in a digital circuit.
What are photoresistors?
Photoresistors, also known as light-dependent resistors (LDRs), are a type of resistor that changes its resistance value based on the amount of light it is exposed to. When exposed to more light, their resistance decreases; in the dark, their resistance is higher. They are often used in light-sensing applications.
How can resistors be used to protect a circuit from surges?
Resistors can be used in a surge protection circuit to limit the current during a surge event, protecting the other components in the circuit. They are often used in combination with other components, such as varistors or TVS diodes, which clamp the voltage during a surge.
What’s a “voltage drop” in a resistor?
Voltage drop across a resistor refers to the decrease in electrical potential as electric current moves through the resistor.
According to Ohm’s Law, the voltage drop (V) across a resistor is equal to the product of the current (I) passing through the resistor and the resistance (R) of the resistor (V = IR).
What does “biasing” mean, and how are resistors used for this purpose?
Biasing refers to the method of establishing a set DC operating voltage or current in an electronic circuit to set appropriate operating conditions for components. In a transistor, for instance, resistors are used to create a desired DC voltage and to ensure the transistor operates in the correct region of its output characteristics.
What are the “legs” of a resistor called?
The “legs” of a resistor are known as leads. These leads are typically made of a conductive material (like copper or silver) and are connected to the resistive material inside the component. The leads allow the resistor to be connected to other components in an electronic circuit.
What is the significance of resistor “noise”?
All resistors generate some amount of noise, which is a small, random AC voltage that’s superimposed on the desired signal. This noise can degrade the performance of a circuit, especially in sensitive applications like audio or radio signal processing. The amount and type of noise depend on the type of resistor and the applied voltage and current.
What is a “series resistor”?
A series resistor refers to a configuration where resistors are connected in a line, end-to-end. In this setup, the total resistance is the sum of the individual resistances. A series resistor configuration is often used when a specific voltage drop is needed in a circuit, or when limiting the current through a component.
How are resistors used in a “bridge circuit”?
In a bridge circuit, resistors are used to create a balance between two voltage dividers. The most common example is a Wheatstone bridge, which is used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown resistance.
What are the consequences of using a resistor with a wattage rating that’s too low?
If a resistor is used beyond its wattage or power rating, it can overheat, which may cause it to fail and could even result in damage to the overall circuit. This is why it’s important to use resistors with a power rating that’s appropriate for the expected power dissipation in the application.
How are resistor values indicated in a schematic diagram?
In a schematic diagram, resistor values are typically indicated next to the resistor symbol. The value is usually given in ohms (Ω), kilohms (kΩ), or megohms (MΩ). Sometimes, the power rating and tolerance are also indicated.
What is a “potentiometer” and how does it function as a variable resistor?
A potentiometer is a type of variable resistor that allows the resistance to be adjusted over a continuous range. It usually has three terminals: two fixed points at either end of a resistive strip and a third one connected to a movable contact.
By adjusting the position of the contact, you can control the resistance between it and the fixed points, effectively varying the resistance.
What is an LDR (Light Dependent Resistor)?
An LDR, or Light Dependent Resistor, is a type of resistor whose resistance decreases when the intensity of light increases. It is made of a high-resistance semiconductor.
In the dark, an LDR can have a resistance of several megohms (MΩ), while in the light, its resistance can drop to a few hundred ohms. LDRs are commonly used in light-detecting circuits and light-sensitive triggering mechanisms.
What is a “fixed resistor”?
A fixed resistor is a resistor that has a resistance value that cannot be changed. They are the most commonly used type of resistor and come in a variety of types, including carbon film, metal film, and wire-wound, among others. Fixed resistors are used in a wide variety of applications to set, limit, or reduce current flow.
What do “linear” and “nonlinear” mean in the resistors?
“Linear” and “nonlinear” refer to the relationship between voltage and current in a resistor. In a linear resistor, the voltage and current are directly proportional (as stated by Ohm’s Law, V=IR), meaning the resistor obeys Ohm’s Law at all times.
Nonlinear resistors, however, do not have this direct proportionality between voltage and current, and their resistance can vary with voltage, current, or other factors.
What are varistors and how do they differ from regular resistors?
Varistors are voltage-dependent resistors, which means their resistance changes as the voltage across them changes.
Unlike regular resistors, where resistance remains constant regardless of the voltage applied, varistors have a nonlinear, non-ohmic current-voltage characteristic. They are commonly used for suppressing voltage surges in electronic devices and systems.
What are the common ways to connect resistors in a circuit?
The two common ways to connect resistors in a circuit are in series and in parallel. In a series connection, resistors are connected end-to-end, and the same current passes through each resistor.
The total resistance is the sum of the individual resistances. In a parallel connection, resistors are connected across the same two points, and the same voltage is applied across each resistor.
The total resistance is found using the formula 1/R_total = 1/R1 + 1/R2 + 1/R3 + …
What are trimmer resistors?
Trimmer resistors, or trim pots, are a type of variable resistor that is often used for calibration, tuning, and adjusting circuit elements. They are designed for occasional adjustments only, with a small screwdriver or similar tool used to change the resistance.
Trimmer resistors can be found in circuits where fine-tuning of the resistance is necessary, such as in calibration circuits.
What is a ballast resistor and where is it used?
A ballast resistor is used to limit the current through an electrical component to a safe or desired level. One common application of ballast resistors is in controlling the current flow through light bulbs in an automobile or fluorescent lights. These resistors help to prevent excessive current, which could otherwise cause a bulb to burn out prematurely.
How do we measure the value of a resistor?
A resistor’s value can be measured using a multimeter, an electronic measuring instrument that combines several measurement functions in one unit. The multimeter is set to the resistance measuring function, then its probes are connected across the resistor. The value displayed on the multimeter is the resistance value.
What is an attenuator and how are resistors used in it?
An attenuator is an electronic device that reduces the power or amplitude of a signal without introducing distortion. Resistors in an attenuator are arranged in a network to provide a certain amount of resistance to the signal, thus reducing its power. These devices are commonly used in audio and radio signal processing.
What is a sense resistor?
A sense resistor, also known as a current-sense or shunt resistor, is used to measure the current flowing through a circuit. It is a precision resistor with a known small resistance. By measuring the voltage across the sense resistor and knowing its resistance, the current can be determined using Ohm’s Law (I = V/R).
What is the difference between a potentiometer and a rheostat?
Both a potentiometer and a rheostat are types of variable resistors, but they are used differently. A potentiometer is often used to vary the voltage in a circuit and typically has three terminals.
On the other hand, a rheostat is used to vary current and usually has two terminals. A rheostat is essentially a two-terminal subsection of a potentiometer.
How can we identify a resistor in a circuit board?
Resistors in a circuit board can often be identified by their physical appearance (a small cylindrical component with a wire lead on each end) and by their color bands, which denote their resistance value.
Surface mount resistors, which are much smaller, can be identified by their small rectangular shape and may have numeric codes to denote their values.
What happens if a resistor is short-circuited in a circuit?
If a resistor is short-circuited, it would mean a path of lower resistance has been created, and the current will follow that path instead of going through the resistor. This could result in higher current flow in the circuit, potentially leading to damage of other components or the power source.
What is a decoupling resistor?
The term “decoupling resistor” is not commonly used. Instead, decoupling is usually associated with capacitors rather than resistors. A decoupling capacitor is used in an electronic circuit to prevent unwanted coupling of signals between circuit stages or to provide a temporary power source that reduces the impact of current or voltage spikes.
What is a series-parallel resistor circuit?
A series-parallel resistor circuit is one where some resistors are arranged in series and others in parallel. This configuration combines the characteristics of both series and parallel circuits.
The total resistance of the circuit can be calculated by first summing the resistances in series, and then calculating the total parallel resistance.
What is a Zener diode and how is a resistor used with it?
A Zener diode is a type of diode that allows current to flow in the reverse direction when a certain specific voltage (the Zener voltage) is reached.
A resistor is often used in series with a Zener diode to limit the current flowing through the diode. Without this resistor, the diode might be damaged by excessive current when the voltage across it exceeds the Zener voltage.
What is the function of a resistor in an RC (Resistor-Capacitor) circuit?
In an RC circuit, the resistor and capacitor work together to create an effect known as the “time constant,” which affects the charging and discharging rate of the capacitor. The resistor limits the current flowing into the capacitor, slowing down the rate at which it charges or discharges.
The time constant of an RC circuit is the product of the resistance and the capacitance (τ=RC) and represents the time it takes for the capacitor to charge or discharge approximately 63% of its maximum value.
What is a grid resistor?
A grid resistor is used in vacuum tube (or valve) circuits. It is connected to the control grid of the tube and functions to limit the flow of grid current and define the input impedance of the tube.
The grid resistor plays a critical role in the overall operation and stability of a vacuum tube amplifier circuit.
How do resistors control voltage?
Resistors control voltage through a principle called voltage division. In a series circuit, the total voltage provided by the power source is divided among the resistors in proportion to their resistances.
By using resistors of different values, you can create different voltage drops across each resistor and thus control the voltage at various points in the circuit.
What happens if a resistor fails or burns out in a circuit?
If a resistor fails or burns out, it will often open the circuit, preventing current from flowing past that point. This may cause the circuit to stop functioning. If the resistor fails short (which is less common), it would provide a path of very low resistance, potentially causing excessive current and damage to other components.
What is the power dissipation of a resistor and how can it be calculated?
Power dissipation of a resistor refers to the power that the resistor converts from electrical energy to heat energy, which is then radiated into the surrounding environment. It is calculated using the formula P = I^2R, where P is the power dissipation, I is the current through the resistor, and R is the resistance of the resistor.
Alternatively, power can also be calculated as P = V2/R, where V is the voltage across the resistor. It’s important to ensure that a resistor’s power dissipation doesn’t exceed its rated power, or it could overheat and fail.