Found 1006 Articles for Electronics & Electrical

The resistances of the values of less than or equal to 1 Ω are classified as low resistances. For example, the resistances of armatures and series windings of large machines, ammeter shunts, contacts, etc.Measurement of Low ResistancesFor the measurement of low resistances, the following methods are used −Ammeter-Voltmeter MethodPotentiometer MethodKelvin Double Bridge MethodAmmeter – Voltmeter MethodIn this method, current through the unknown resistor (Rx) and the potential drop across it are simultaneously measured. The readings are obtained by ammeter and voltmeters respectively. There are two ways in ammeter and voltmeters may be connected for measurement as, Case 1 – When voltmeter ... Read More

Resistances of the order of 100 kΩ and upwards are classified as high resistances. For example, insulation resistances.Measurement of High ResistancesThe following methods are employed for the measurement of high resistances −Direct Deflection MethodLoss of Charge MethodMegohm BridgeMeggerDirect Deflection MethodIn this method, a very sensitive and high resistance (more than 1 kΩ) PMMC galvanometer is connected in series with the resistance to be measured and to a battery. The deflection of galvanometer gives the measure of unknown resistance. This method is mainly used for the measurement of insulation resistance.Let us take an example of direction deflection method for measuring insulation ... Read More

Resistance in an AC CircuitConsider the circuit diagram, containing an AC sinusoidal voltage source and an unknown passive element (K). The element K will be a resistance, only if the voltage across it and the current flowing through it, are in phase with each other.ExplanationLet the equation for alternating voltage is$$\mathrm{v=V_{m}\sin\omega\:t\:\:\:...(1)}$$As a result of this voltage, an alternating current i will flow through the element. Now, the applied voltage has to overcome the drop in the element only, i.e.$$\mathrm{v=i\times\:k}$$$$\mathrm{\Rightarrow\:i=\frac{v}{k}=\frac{V_{m}\sin\omega\:t}{k}\:\:\:...(2)}$$The value of current will be maximum, when sin(ωt) = 1.$$\mathrm{\therefore\:I_{m}=\frac{V_{m}}{K}}$$Thus, the equation (2) becomes, $$\mathrm{i=I_{m}\sin\omega\:t\:\:\:...(3)}$$It is clear from the eqns. (1) ... Read More

One of the remarkable discoveries in the field of electrical engineering is the grounding of electric current. In an electric circuit, there be an active wire, which supplies current and a neutral wire, which carries that current back. An additional grounding wire can be attached to outlets and other electrical devices and also securely connected to the ground. This ground wire provides an additional path for the current to return safely to the ground without danger to anyone, when short circuit occurs.The purpose of grounding the utility power distribution becomes clear from following points −Protection against electrical overloadOne of the ... Read More

The power transformers are design to operate with an almost constant load which is equal to their rating. The maximum efficiency being designed to be at full load. Therefore, the fullload winding copper losses must be equal to the core losses.Actually, all the transformers are the same that is same design formulae apply for small signal transformers to the power transformers. In case of power transformers, the designer needs to consider both voltage and current, to remember that heat will need to be dissipated and the series resistance is a cause of low efficiency.Therefore, a power transformer has the following ... Read More

Power in AC circuitActive Power (P)The product of voltage (RMS) and current (RMS) with the cosine of the angle between them, in an AC circuit is termed as active power. It is measured in watts (W). For a pure inductive and pure capacitive circuit, the active power being zero.Active Power, P = VI cos φReactive Power (Q)The product of voltage (RMS) and current (RMS) with sine of the angle between them, in an AC circuit is known as reactive power. It is measured in VAR (Volt-Ampere Reactive).Reactive Power, Q = VI sin φApparent Power (S)The product of voltage (RMS) and ... Read More

An oscilloscope is a device which allows the amplitude of electrical signals (current, voltage, power etc.) to be display as a function of time.Oscilloscope Parts and their FunctionAn oscilloscope consists of following major parts (see the block diagram) −Cathode Ray Tube (CRT) – The CRT displays the quantity being measured. It generates and accelerates an electron beam, deflects the beam to create the image and contains a phosphor screen where the electron beam eventually becomes visible.Vertical Amplifier –The vertical amplifier amplifies the waveform of the signal to be viewed.Horizontal Amplifier – The horizontal amplifier is fed with a saw-tooth voltage ... Read More

A device that can measure the resistance directly is known as an ohmmeter. There are two types of ohmmeters asSeries Types OhmmeterShunt Type OhmmeterSeries Type OhmmeterCircuit DiagramThe circuit of a series type ohmmeter consists of a D’Arsonval galvanometer (PMMC meter) connected in series with a resistance and a battery. It has two terminals (A and B) to which the unknown resistance (Rx) is connected.Since the meter and unknown are in series, the current through the meter depends upon the value of unknown resistor. The meter indication is directly proportional to the value of unknown resistor, provided that calibration problems are ... Read More

When the two coils are arranged in such a way that a change of current in one coil causes an emf to be induced in the other, the coils are said to have mutual inductance. The mutual inductance is denoted letter M and measured in Henry.Consider two coils, coil 1 and coil 2 placed adjacent to each other. When a current I1 flows in the coil 1, a magnetic flux (Φ1) is produced in it and some part of the Φ1 links with the coil 2 and is known as mutual flux (Φm).Now, if the current in the coil 1 changes, ... Read More

The Magnetomotive force (MMF) is defined as the work done in moving a unit magnetic pole once around the magnetic circuit. It is a magnetic pressure that tends to set up magnetic flux in a magnetic circuit. Mathematically, the mmf is the product of current and number of turns of a coil.Consider the coil consisting of N turns and an electric current of I amperes flowing in it. Therefore, the mmf is given by, Magnetomotive force, MMF = 𝑁𝐼 … (1)Unit of MMFSince MMF is a product of current in amperes (A) and number of turns (T) in a coil, ... Read More