#electronics tutorials

What is Resistor?

Resistor Symbols

Resistance

Resistance Measurement

What is Resistor?

A resistor may be a device during which electricity cannot undergo it easily. When specific amount electricity is allowed to undergo a resistor, the electricity is modified into another form. the opposite sort of energy is typically light or heat. The working rule of bulb is that electricity is skilled the filament usually tungsten, which may be a resistor. The energy is converted to and released as light and warmth .

The resistor is an electrical component which creates a resistance within the flow of electrical current.

A resistor may be a basic electrical component found in most electronic circuits and electrical networks. A resistor is 2 terminal passive electrical component. it’s a passive component because it consumes energy from a source (active component).

Although resistors are generally wont to reduce the flow of current or lower the amount of voltage during a circuit, they’re utilized in many electronic circuits for several purposes. a number of them are the essential current flow limitation ability, to supply a biasing condition to a number of the active elements like transistors or to act as a terminating device in transmission lines.

Practically resistors are discrete components of varied forms but also are implemented on integrated circuits.

Resistor Symbols

Generally there are two standards that are wont to denote the symbol of a resistor viz. Institute of Electrical and Electronics Engineers (IEEE) and International Electro Technical Commissions (IEC).

The IEEE symbol of resistor may be a zigzag line as shown within the below figure.

Resistor Symbol

The IEC symbol for resistor is shown below.

There are another symbols of resistors in use , supported the sort . Each type has both IEEE symbol and IEC symbol. the kinds of resistors are potentiometer and rheostat which is usually referred to as rheostat.

The IEEE symbol for potentiometer is shown below.

The IEC symbol for potentiometer is

The IEEE symbol for rheostat is

The IEC symbol for rheostat is

Resistance

The mechanism of energy flow through a conductor are often described as follows: within the presence of a lively source, the passive elements like resistors will always absorb energy and therefore the currents through them will always be due higher potential to lower potential.

If we apply an equivalent electric potential between the ends of two different but geometrically similar conductors like rods of copper and of glass, it leads to different currents. This characteristic of the conductor that leads to different currents is its electric resistance .

The definition of resistance are often derived from the Ohm’s law in its Electromagnetic theory form or Continuum form:

J = σ E —- 1

Here σ is that the conductivity of the fabric i.e. conductor.

E is that the field developed along the length of conductor thanks to flow of electricity through the conductor.

If ‘V’ is that the drop across the conductor and ‘L’ is that the physical length of conductor then

E = V/L ————– 2

The current density J is resulted within the conductor thanks to the flow of electricity through the conductor.

If ‘I’ is that the current flowing through the conductor and ‘A’ is that the cross sectional area of conductor, then by the definition of current density

J = I/A —————– 3

Now combining equations 1, 2 and 3

I/A = σ V/L

=> V = (L/Aσ)I —————- 4

The term in parenthesis is constant and allow us to denotes it by ‘R’.

∴ V = R I

This is the Ohm’s law form in circuit analysis.

By the definition of Ohm’s law, the present flowing through a conductor is directly proportional to the electric potential applied.

I ∝ V

The proportional constant is named Resistance parameter of the conductor R.

∴ I = V/R

R = V/I

The resistance of a conductor, between its two points is decided , by applying a possible difference V between those two points and measuring the present I .

The unit of resistance is Volts per Ampere and is given the name Ohm (Ω).

∴ 1Ω = 1 volt per ampere = 1 V/A.

From earlier calculations,

V = (L/Aσ) I

∴ R = (L/Aσ)I

σ is that the conductivity of the conductor which is that the measure of conductor’s ability to conduct current .

1/σ is that the reciprocal of electrical conductivity called electrical resistivity denoted by the symbol ρ (rho).

Resistivity is that the measure of a conductor’s ability to resist the flow of electrical current.

∴ Resistance of a cloth ∝ resistivity of the fabric .

R = (ρL/A) Ω

Resistance of a conductor are often defined because the conductor’s opposition to the flow of current through it.

Resistance may be a property of an object like conductor. Resistivity may be a property of a cloth from which the thing is formed .

The definition of resistor are often written as:

A conductor whose function is to supply a specified resistance during a circuit.

Resistance Measurement

Resistors are main components in electric and electronic circuits as they determine the quantity of current that flows during a circuit and also the potential at different points during a circuit. Therefore it’s important to form sure that the worth of resistance is understood for a given resistor which is placed during a circuit.

From Ohm’s law, it’s easy to calculate the resistance. Ohm’s law relates the Voltage V, Current within the circuit I and therefore the Resistance of the resistor R.

R = V/I

∴ In terms of units, 1 Ohm (Ω) = 1 Volt (V) / 1 Ampere (A).

In other terms, a resistor is claimed to be having a resistance of 1Ω when 1A of current is skilled it for a supply voltage of 1V.

Ohmmeter may be a device designed specifically for this purpose. A resistor is connected across the terminals of ohmmeter and therefore the reading of the ohmmeter is that the value of the resistance of that resistor along side the resistance offered by the wires wont to connect the resistor to ohmmeter.

Even though the resistance of wire is extremely small, it can’t be neglected. Hence the values measured using an ohmmeter isn’t accurate.

The next best thanks to determine the resistance is to form use of both voltmeter and an ammeter within the circuit.

The setup are often as follows:

In this method, the readings both current and voltage are taken using the respective devices. If we consider the resistances of the wire then the circuit will be

Since it’s a series loop, current are going to be same in the least the points. Because the voltmeter is employed to live the drop across the unknown resistor, wire resistances doesn’t inherit picture.

∴ RX = Voltmeter Reading / Ammeter Reading

The above setup is sweet if internal resistance of the voltmeter is larger compared to the RX.

In case of resistance RX is larger than that of internal resistance of the voltmeter then the subsequent setup are often used.

Another technique is employed for the measurement of lower resistances. this is often called Four Terminal Sensing or Kelvin Sensing.

To measure the lower resistance (< 100Ω), the Kelvin Sensing is employed to eliminate the inappropriate influence of contact resistances and wiring resistances.

This connection method for resistance measurement uses separate pairs of current-carrying and voltage-sensing probes to eliminate the influence of contact and test lead resistances which appear within the precious setup which is additionally called Two Terminal Sensing.

The four terminal sensing method with internal resistances of wire can be depicted as follows:

The resistance of Rx1 are often calculated as follows:

The current which passes through the voltage-sensing path or terminals is extremely but the present through the resistor RX1. this suggests that the drop across the wire resistances within the voltage-sensing path is extremely less.

∴ I = IRX1 + IVPath ≈ IRX1

Now the voltage across the resistor RX1 is that the value of voltmeter VRX1.

∴ RX1 = VRX1 / IRX1

Resistivity

Often the power of a cloth to conduct electricity or the electrical transport property of a cloth is measured by the conductivity of the fabric .

Electrical Conductivity of a cloth is that the measure of its ability to conduct current.

Resistivity is that the reciprocal of conductivity. Resistivity is that the measure of a conductors’ ability to resist the flow of electrical current.

Derivation:

Assume a cloth of length ‘ L’ and area of cross section ‘A’ and resistance ‘R’.

Resistance to the of the fabric is directly proportional to the length ‘L’ and inversely proportional to area of cross section ‘A’.

Thus,

R ∞ L,

R ∞ 1/A,

Combining above two equations,

R ∞ L / A

Assume a continuing ‘ρ’ to eliminate proportionality.

So, R = (ρ ×L) /A.

Hence ρ = (R×A) / L.

Thus from above equation materials with low resistivity allows the movement of electrons while those with high resistivity oppose the flow of electrons.

Elements like copper, aluminum will have low resistivity

Units of resistivity are Ohm-meter (Ω-mt).

In mathematical terms, the definition of resistivity is resistance per unit length per unit cross sectional area of the fabric .

In electromagnetic theory, the term resistivity are often defined because the magnitude of electrical field across the fabric that leads to a particular current density.

ρ = E / J

E is that the electrical field and J is that the current density.

Resistance Example 1

If a rectangular block of iron (with ρ = 9.68 * 10-8 Ω.m) of dimensions 1.2cm x 1.2cm x 15cm is applied with a potential difference such that the sides are equipotential, find the resistance.

Solution:

L = 15cm = .15m

A = 1.2cm * 1.2cm = 1.44 * 10-4 m2

∴ R = ρL/A

R = (9.68 * 10-8 Ω.m * .15m) / (1.44 * 10-4 m2)

R = 1 * 10-4Ω = 1µΩ

Units Of Resistance

Resistance R = V/I

This results in the units of resistance as volts per ampere. This combination is given a special name called Ohm named after the physicist Georg Simon Ohm.

∴ 1Ω = 1volt per ampere

The units of conductance which is reciprocal of resistance is given by 1/Ω and given the name Mho. Mho is Ohm written in reverse. It is given by the symbol ℧. Later this is changed to Siemens (S).

S = Ω-1 = A/V.

The value of Ω can be defined in various forms as shown in the below equation

Where

Ω is the Resistnace

V is Volts

A is Ampere

Kg is Kilogram

m is Meter

s is Second

C is Coulomb

J is Joule

S is Siemens

F is Farad

W is Watt

Carbon Resistors

Carbon Composition Resistors are commonly used resistors which are manufactured at low cost. this is often due to the simpler construction process. they’re generally called carbon resistors. the most composition is carbon clay which is roofed during a plastic case and therefore the leads are made from tinned copper. the most advantage of carbon resistors is that they’re easily available at very low cost in the least local vendors and therefore the durability is sweet . the sole disadvantage is that they’re very sensitive to temperature.

Carbon resistors are often manufactured in wide selection of values as low as 1 Ω value to a high value as 22 MΩ. thanks to its low cost, they’re utilized in circuits where cost may be a criterion instead of the performance.

Working of Resistance

The principle behind the working of resistor are often explained using hydraulic analogy. allow us to imagine a pipe with water flowing through it. If we make the diameter of the pipe small, the flow of water is restricted. Now we increase the force of water through an equivalent reduced diameter by increasing the pressure, then the energy are going to be dissipated in other form.

The difference in pressure at both the ends of the pipe is critical . Now we apply this analogy to an electrical system i.e. force applied to water is like current through a resistor and applied pressure is like voltage.

The reason for this alteration within the sort of energy are often explained as follows. The high electrical conductivity of metals is beneficial because it has free flow of electrons and this flow of charge is named current . But when the flow of electrons isn’t free i.e. restricted, the electricity is converted in to other forms like heat just in case of poor conductors. This restriction of flow of electrons without completely stopping it’s the thought behind resistors.

This principle of restricted flow of electrons might not need to be wont to get heat as output but has other functions like reduction in voltage or current, emission of sunshine etc.

V-I Characteristics of a Resistor

V-I Characteristics of a resistor are the relation between the applied voltages and therefore the current flowing through it.

From Ohm’s law, we all know that when the voltage applied across the resistor increases, the present flowing through it also increases i.e. the voltage applied is directly proportional to current. The V-I characteristics graph are often determined from the subsequent circuit:

The graph like the circuit for the function v(t) = R i(t) which is within the sort of y = mx is as shown below. To plot the graph, the values of voltage (V) are taken on the y-axis and therefore the values of current (I) are taken on the x-axis. From the graph it’s clear that V-I characteristics of a resistor are linear and therefore the value of the resistance at any instance are often determined by the slope of the curve at that instance.

The above specifications are valid in case of a pure resistance i.e. ideal resistor and the temperature is constant. In practical conditions, these values may vary depending on the operating environment and the characteristics might be different from the ideal linear values.

Variation of Resistance with Temperature

As the temperature of the environment increases the resistance of the fabric changes. The reason for this alteration isn’t due to the variations within the dimensions of the fabric but rather the change within the resistivity of the fabric . When there’s an increase within the temperature, the warmth will cause an atomic vibration and therefore the se vibrations will cause a collision between the free electrons and the electrons within the inner layers of the atom. These collisions will use the energy of free electrons. If more collisions happen , more energy of electron is employed and increases the resistance to flow of current. this is often the case in conductors. In case of insulators the resistance decreases with increase in temperature. The reason is that the availability of number of free electrons which are released from its captive stage. In mathematical terms, a fractional change in resistance is directly proportional to the change within the temperature. In mathematical terms, a fractional change in resistance is directly proportional to the change within the temperature.

∆R/R0∝∆T

Where ∆R is that the chickenfeed in resistance

∆R = R – R0

R is resistance at temperature T

R0 is resistance at temperature T0

∆T is change in temperature

∆T = T – T0

If we denote the proportionality constant within the above equation as alpha (α)

Then ∆R/R0 = α∆T

Where α is that the temperature coefficient of the resistance.

The temperature coefficient of resistance is employed to explain the relative change in resistance in association with change in temperature.

If the change in temperature is little then the above equation are often written as

R = R0 [1+α (T-T0)]

If the resistance increases with increase in temperature, then the fabric is claimed to be having a positive temperature coefficient. These materials are conductors.

If the resistance decreases with increase in temperature, then the fabric is claimed to be having a negative temperature coefficient. These materials are insulators.

 Learn About Capacitors

Introduction to Capacitors

Types of Capacitors

Capacitor Characteristics

Capacitance and Charge

Capacitor Color Code

Capacitors in Series and Parallel

Capacitive Voltage Divider

Capacitance in AC Circuits

Applications of Capacitors

Basic Electronics Tutorials Complete Tutorials click here

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Introduction

Table Of Capacitor Applications

Filter Applications

Decoupling/By-Pass Capacitors

Introduction

Capacitor is one among the passive components and it stores energy within the sort of electrical charge. Capacitor charges and discharges the charge counting on the circuit operation. it’s used mainly in electronic and electrical circuits to perform different tasks, like smoothing, filtering, bypassing, noise reduction, sensing capabilities and etc.

One application requires one sort of capacitor and another application requires another sort of capacitor. i.e. same sort of capacitor isn’t used for all the applications. First of all we’d like to settle on which sort of capacitor is suitable for a specific application. Choosing of capacitor type depends on some factors. The factors which influences in choosing sort of a capacitor for a selected application are given below,

Capacitance Value Ranges: Each sort of capacitor available during a specific range. counting on application we’d like to settle on a required range of capacitor.

Working Voltage: Some sorts of capacitors have low working voltages and a few more sort of capacitors have high working voltages. counting on the appliance we’d like to settle on the capacitor voltage.

Polarization: Tantalum and electrolytic capacitors are polarized and also they operate with a voltage in one direction. So polarization is one among the important factors while choosing the capacitor.

Tolerance: The close tolerance value capacitors are needed to settle on for applications like oscillators and filters where the capacitor value is critical. But in some sort of applications like coupling and de-coupling the worth of capacitor isn’t critical.

Temperature Coefficient: Capacitance value varies with temperature in some sort of capacitors and a few capacitors like silver mica, ceramic are stable with varying temperatures. So counting on application one can select the capacitor.

Leakage Current: High level insulation is required in some applications but in some applications it’s not necessary. Electrolytic capacitors have poor leakage performance. Leakage current is additionally considerable factor while choosing the capacitor for application.

Cost: the value is that the basic driving parameter for all applications. Because everyone want to possess high performance with low cost. Today, all the high performance capacitors are available for low cost in surface mount packages.

Table Of Capacitor Applications

A capacitor is employed in electronic circuits depends on the appliance and requirements. Each application requires a selected sort of capacitor for specific use. The capacitors with their uses and applications are given within the tabular form for better understanding. Please undergo the table given above to know easily about capacitor applications and uses.

Filter Applications

Capacitors are used as main elements in frequency selective filters. All the filter designs are used for the high performance and frequency based applications, by selecting the right components and quality required. a number of the filter topologies are given below.

Low Pass Filter (LPF)

Band Pass Filter (BPF)

Band Stop Filter (BSF)

Notch Filter (NF)

All Pass filter (ALF)

Equalization Filter (EF)

Decoupling/By-Pass Capacitors

Decoupling capacitors are utilized in digital electronics to guard the microchips from the electrical noise on power signals. the most role of decoupling capacitors is to scale back the noise within the circuit. These capacitors are placed very on the brink of the microchips within the circuits to get rid of noise from the environment . These capacitors also are provides extra energy to the IC’s and also remove disturbances to the logic signal.

Coupling or DC Blocking Capacitors

The coupling or DC blocking capacitors are utilized in the applications where the AC and DC signals are got to be separated. These sorts of capacitors will allow only AC signals and blocks the DC signals. Here the capacitance value of a capacitor won’t affect the coupling applications.

But the performance of those capacitors is high within the applications if the reactance of a capacitor is high value. the most use of those capacitors is to dam the DC currents from the signal. These sorts of capacitors are wont to pass AC signals for coupling of 1 electronic circuit to a different circuit.

Snubber Capacitors

Snubber capacitors are utilized in the circuits where high inductance load is driven. In high inductance circuits, like in transformers and in motors the stored energy is discharged suddenly. thanks to this effect other components within the circuit may damage and also large power spikes are obtained in those circuits. To avoid these problems we use capacitors across the high inductive components within the circuits. thanks to this process the capacitors avoid voltage spikes and also they supply safety to the circuit.

Low power circuits also use these snubber capacitors to avoid voltage spikes, which are created from undesirable frequency (RF) interferences, which influences the circuit operation. These snubber capacitors also are utilized in parallel to the interrupt components, within the high voltage circuits to avoid breaker problems by producing equal voltage distribution between those components.

Pulsed Power Capacitors

Generally a capacitor is little energy storage component. Large capacitors and capacitor banks are used where tons of energy required within a brief period of your time . Capacitor banks store the lot of energy for the applications, like particle accelerators, pulsed lasers, radars, max generators, fusion research and rail guns. a traditional application for pulsed power capacitors is employed during a flash on disposable camera which charges up and discharges quickly through its flash.

Resonant or Tuned Circuit Applications

To design filters we use capacitor, resistors and also inductors. during this design some combinations of components are used, to amplify the resonant frequency signals. Here the low power signals are amplified to the high power signals, at resonant frequency, as tuned filters or oscillators. But in designing the resonant frequency circuits we take much care about the component combinations because a number of the combinations are may damage the operation and also fail quickly.

Capacitive Sensing Application

The capacitive sensing may be a technique in detecting the change in capacitance value, change within the distance between the plates, change in dielectric and alter within the area of capacitor plates. Capacitive sensing may be a technique which is recently utilized in advanced consumer electronic circuits. Although capacitive sensors are utilized in different applications like position, fluid level, humidity, acceleration and manufacturing internal control etc.

Capacitor Safety

We need to require some safety precautions about capacitors. Capacitors are storage devices, which store electricity from small amounts to large amounts. thanks to this high energy we will observe electrical charge albeit the facility is disconnected. Sometimes these high energy capacitors may damage the circuit components. One neatest thing to avoid these problems is discharge the capacitors before use within the electrical circuits.

If the voltage to the polarized electrolytic capacitors are reversed then these capacitors may fail within the circuit operations. The breaking of dielectric material also causes to fail the capacitors albeit they’re utilized in high voltage and high power applications.

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Introduction

AC Capacitor Circuit

AC Capacitor Phasor Diagram

Capacitive Reactance

Introduction

When DC supply voltage is applied to the capacitor, the capacitor is charged slowly and eventually it reaches to completely charged position. At now the charging voltage of a capacitor is adequate to the availability voltage. Here the capacitor acts as an energy source as long as voltage is applied. Capacitors don’t allow current (i) through them after they fully charged. the present flowing through the circuit depends on the quantity of charge within the plates of capacitors and also the present is directly proportional to the speed of change of voltage applied to the circuit. i.e. i = dQ/dt = C dV(t)/dt.

If AC supply voltage is applied to the capacitor circuit then the capacitor charges and discharges continuously counting on the speed of frequency of supply voltage. The capacitance of a capacitor in AC circuits depends on the frequency of supply voltage applied thereto . In AC circuits the capacitors allow current when the availability voltage is continuously changing with reference to time.

AC Capacitor Circuit

In the above circuit we observed that a capacitor is directly connected to the AC supply voltage. Here the capacitor continuously charges and discharges counting on the changes in supply voltage, because the AC supply voltage value is consistently increases and reduces . We all know that the present flowing through the circuit is directly proportional to the speed of change of voltage applied.

Here the charging current has its high value, if the availability voltage crosses its value from positive half cycle to the negative half cycle and the other way around . i.e. at 00 and 1800 in wave signal. the present through the capacitor has its minimum value when the availability voltage in wave crosses over at its maximum or minimum peak value (Vm). Hence we will say that the charging current flowing through the circuit is maximum or minimum counting on the availability voltage levels in wave .

AC Capacitor Phasor Diagram

The phasor diagram of AC capacitor is shown within the above figure; here the voltage and currents are represented in wave forms. within the above figure we observed that at 00 the charging current is at its maximum value because the voltage is increasing slowly in positive direction. At 900 there’s no current flow through the capacitor because at now the availability voltage is at its maximum peak value.

At 1800 point the voltage slowly decreases to zero and current is at maximum value within the negative direction. Again the charging reaches to its maximum value at 3600, because at now the availability voltage is at minimum value.

From the waveforms within the above figure we will see that, the present is leading the voltage by 900. Hence we will say that in a perfect capacitor circuit the AC voltage lags the present by 900.

Capacitive Reactance

We know that the present flowing through the capacitor is directly proportional the speed of change of applied voltage but capacitors also offer some sort of resistance against the present flow same as like resistors. This resistance of capacitors in AC circuits is named as capacitive reactance or commonly referred to as reactance. Capacitive reactance is that the property of a capacitor which opposes the flow of current in AC circuits. it’s represented with symbol Xc and measured in Ohms same as like resistance.

We need some extra energy over capacitive reactance to agitate a capacitor within the circuit. This value is inversely proportional to the capacitance value and therefore the frequency of supply voltage.

Xc ∝ 1/C and Xc ∝ 1/f.

The equation for capacitive reactance and parameters which influences them are discussed in below.

Capacitive Reactance,

XC = 1/2πfC = 1/ωC

Here,

XC = Reactance of capacitor f = frequency in Hz C = Capacitance of a capacitor in Farads ω (omega) = 2πf

From the above equation we understood that capacitive reactance is high where the frequency and capacitance values are at low and at this stage the capacitor acts as an ideal resistor. If the frequency of supply voltage is high then the reactance value of capacitor is low and also at this stage capacitor acts as an honest conductor. From the above equation it’s clear that the reactance is zero if the frequency is infinity and therefore the reactance value is infinity where the frequency is at zero.

Capacitive Reactance Against Frequency

The above figure shows the relation between the capacitive reactance, current and frequency of the availability voltage. Here we observed that if frequency is low then the reactance is high. The charging current increases with increase in frequency, because the speed of change of voltage increases with time. The reactance is at infinite value where the frequency is zero and the other way around .

Question 1 AC Capacitance

Find the rms value of current flowing through the circuit having 3uFcapacitor connected to 660V and 40Hz supply.

Capacitive Reactance,

XC = 1/2πfC

Here,

f = 40HZ C = 3uF Vrms = 660V

Now,

XC = 1/(2*3.14*40HZ*3*10-6) = 1326Ω

Irms = Vrms/XC = 660V/1326 Ω = 497mA

Question 2 AC Capacitance

Find the rms value of current flowing through the circuit having 5uFcapacitor connected to 880V and 50Hz supply.

​Capacitive Reactance,

XC = 1/2πfC

Here,

f = 50HZ

C = 5uF

Vrms = 880V​

​

Now,

XC = 1/(2*3.14*50HZ*5*10-6) = 636Ω

Irms = Vrms/XC = 880V/636 Ω = 1.38A​

From the above two examples practically we observed that the reactance of a capacitor depends on the frequency of the supply voltage and it is inversely proportional relation. In example 1 the reactance is 1326Ω for the frequency of 40HZ but the reactance value decreases to 636Ω when the frequency increases to 50HZ which is shown in example 2. Hence it is clear that the reactance of a capacitor is inversely proportional to the frequency and capacitance.​

More About Capacitors

Introduction to Capacitors

Types of Capacitors

Capacitor Characteristics

Capacitance and Charge

Capacitor Color Code

Capacitors in Series and Parallel

Capacitive Voltage Divider

Capacitance in AC Circuits

Applications of Capacitors

Basic Electronics Tutorials Complete Tutorials click here

The post Basic Electronics Tutorials: Capacitance in AC Circuits appeared first on Learn Electronics Technology Online.