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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
What is the unit of measure for reactive power?
Volt Amps [volts times amps] is used for reactive and apparent power. Watts (dimensionally the same as volt amps) is used to indicate real power.
AnswerReactive power is measured in reactive volt amperes (var).
What is ampere rating of a fuse used to protect a 5.5 mm squared conductor?
The equivalent mm2 cross-sectional area of a 5.26 mm2 conductor is a # 10 AWG conductor. A # 10 AWG conductor size is protected by a 30 amp fuse.
How do you calculate voltage using Nernst equation?
The Nernst equation is E = ((-2.3RT)/zF)*(log10 [Ci/Co])
E = equilibrium potential (mV)
z = charge on the ion
(2.3RT)/F = constant (60mV at 37C)
Ci = intracellular concentration
Co = extracellular concentration
The Nernst equation is important because it shows what the equilibrium potential would be for one ion.
E.g. The resting membrane potential is normally ~70mV. So during an action potential Na channels open their gates briefly and Na rush inside the cell. Na is ionized and carries a positive charge. So when Na rushes into the cell it makes the inside of the cell more positive. If you were to break off the gate and allow Na to move freely back and forth, the Nernst equation shows us that the equilibrium point for Na is ~+65mV.
•deltaG - DG0 = R T ln Q
• deltaG = nFE
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•E = E0+ (RT / nF) ln Q
Which circuit draws the largest amount of current from the battery parallel or series?
Well firstly, is the capacitor connected to a DC or AC supply.
On a DC supply the capacitor would draw current until it had fully charged, at which point the current falls to the leakage current. Electrolytic capacitor will always leak a little.
On an AC connection, current will pass continuously, and the capacitor may rupture if connected across an AC supply.
The current that would flow on an AC connection is given by the impedance, which is calculated from the reciprocal of 2 x Pi x F x C
Because it is the reciprocal, the impedance reduces as the capacitance in Farads (F) increases. So, the bigger the capacitance, the higher the current.
Therefore, for AC, only low values of capacitor are found connected across the supply (usually with a resistor in series) for interference snubbing across a contact or switch. Larger values are placed in series with the current, to act as current limiters or high pass filters.
What is the mechanism behind working of weighing machine?
Weight is sensed using a transducer. A weighing machine transducer is usually a spring/piezoelectric component. The resistance of it varies as the weight changes. So does the current through it. This current is sensed, and is converted suitably to output it's weight.
What is formula for kwh in three phase power?
Multiply the power of the load [1.732 x UL IL x power factor], expressed in kilowatts, by the operating time, expressed in hours. This is only practical for a constant load.
What is the formula of energy loss in hysteresis curve?
P/Vol=A/T
P: Power
Vol: Volume
A: Area
T: Period
How many amps are used in 241000 kwh in a 3 phase power system?
The voltage can be either 250000 kilovolts or 240 volts, it can't be both so the question can't be answered.
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There are zero amps in 250,000,000 volts. Amps can be found using the following equations. Amps = Volts/Resistance in ohms, Amps = Watts/Volts and Amps = Sq root of Watts/Resistance in ohms.
What is the main differences between RMS value and average value?
RMS stands for root mean square. This is done so that negative values are then treated as positive values. In AC power for example, the voltage varies between a negative and a positive value. The number is squared and then the square root of this value is taken and the mean (average) of these numbers gives the answer. For example -40 is squared to become 1600 and then the square root of 1600 is taken to become 40 (a negative number becomes a positive number).If this wasn't done then the average value of AC power would be zero.
How are resistor connected in series?
when we want maximum resistance they are connected in series.
when resistors are connected in series total resistance is maximum
when resistors are connected in parallel total resistance is minimum
for series total R=R1+R2+R3.........
for parallel R1 in parallel to R2 total 1/R=(1/R1)+(1/R2) ie R=(R1*R2)/(R1+R2)
What are the factor affecting capacitances of capacitance?
The area of the sheets, the distance between them, and the material between them.
Simply put, a single phase supply has one or two hot wires, may have one neutral wire, and (hopefully) one ground wire. A three phase supply has three hot wires, and may (wye connection) or may not (delta connection) have a neutral. It also will have a ground wire. A more complex explanation involves the phase difference between hot wires. For three phase there is a 120 degree phase difference between each of the three possible pairs of hot conductors A-B, B-C, C-A. For single phase, since there is only one possible pair of hots, there can be no difference.
How does electricity affect human life?
Without electricity the human society goes back to stone age. Almost everything what human does today is with the help of electricity.
People who stay with out electricity are either completely backward and in a state poverty or they are saints in Himalaya.
Can you hook up a delta to delta transformer to be a delta to wye transformer?
The open Delta or V-Connection transformer is an improvement of the 1 three-phase transformer. The open Delta transformer can restore power in a Delta-Delta three-phase bank when one of the three single-phase transformers, which can be individually disconnected and replaced in case of failure, breaks down. The open Delta transformer then allows functionality to be restored, but at a reduced power of 57.7 of the original power.
Why earth fault current is less than short circuit current?
A short circuit occurs when the current pass through earth directly or the current returns to its source without passing the load. It is caused by a very low or zero impedance wire that may be connected line to line or line to ground.
A fault current can be a short circuit but the wire have an impedance that may still give current to the load. the protective device operates when the current exceeds the rating of circuit breaker, by load current + fault current.
Why is dielectric constant for metals is infinity?
It is not infinite. At some extreme values electron-positron pairs will start forming rapidly what will result current flow.
However from practical standpoint vacuum dielectric strength is limited by field emission from electrodes. Best results are about 40MV/m , what is far worse than some good dielectrics can provide.
The amperage rating of a copper wire is related to its resistance and to the type of insulation used (i.e., what temperature the insulation can handle) and the ambient temperature. The fatter the copper wire, the more amps it can handle, everything else being equal. A mineral-insulated wire, buried underground, would handle more amps than a similarly sized copper wire in thermoplastic insulation in air.
There are electrician charts available to determine the MINIMUM size of copper (or aluminum) wire necessary for a particular load.
Consider also that longer the wire, the more resistance there is, so a very long wire would need to be larger to handle the same load safely.
What happens if resistance decreased in earthing?
It will work properly! The resistance and impedance of the earth lead must be low, though the corollary is that it must be capable of passing any likely fault current safely.
A UV air purifier along with a HEPA and carbon filter will help clean the air, not only from airborne particles and smoke, but also from germs.
The UV light is normally added to combat/kill floating fungus and bacteria. If you live in a damp place (near swamp, leaking pipe etc) you'll probably be inhaling spores from molds. This is where a UV light air purifier would be useful.
One of the best known UV air purifier is the Alen A375UV
How would you measure voltage passing through a light bulb using a digital multimeter?
Simply set the multi meter on DC voltage, which is denoted by a line with dotted lines under it. Then place the red lead on the positive side of the bulb and the black lead on the negative side. If you do this incorrectly it will be a negative number but the same number if the leads are reversed.
If you have a bad bulb the meter will show all zero´s. Otherwise you´ll get something like 0.01 which is a good indicator for a working bulb.
The voltage across the light bulb will be the same voltage as the supply. Regardless of whether the bulb is good or bad the voltage potential will still be there. You are measuring voltage not amperage.
How much can you power on a 2.5kva generator?
It can supply 2.5 kW to a load with a power factor of 1. Otherwise the power available must be multiplied by the power factor which is always less than 1. If uncertain assume 0.8 which makes it 2 kW.
How do you calculate actual power factor?
The power factor of a circuit is defined as the cosine of the phase angle -which is the angle by which the supply current lags or leads the supply voltage in AC circuits.
Power factor is always expressed as either a 'lagging power factor' or as a 'leading power factor'.
The terms 'lagging' or 'leading' describe the relationship of the supply current to the supply voltage. Since current lags voltage in an inductive circuit, 'lagging power factors' describe inductive circuits; since current leads voltage in capacitive circuits, 'leading power factors' describe capacitive circuits. In practice, lagging power factors are more common than leading power factors, because most practical loads are inductive (e.g. motors, etc.).
Power factors are normally expressed as a decimal (e.g. '0.8 lagging') although, in the past they were often expressed as a percentage (e.g. '80% lagging'). 'High' power factors tend towards unity, whereas 'low' power factors tend towards zero.
In terms of power, the cosine of a circuit's phase angle and, therefore, its power factor is the ratio of that circuit's true power (expressed in watts) and its apparent power (expressed in volt amperes).
Power factor has no effect whatsoever upon the energy consumed by a load, but it does effect the amount of current drawn from the supply. 'Low' power factors result in unnecessarily-large load currents for any given load, which mean that the supply utilities need to use larger than necessary conductor sizes (expensive!). For industrial or commercial (but not residential) loads, therefore, it is often desirable to 'improve' the load's power factor towards unity, which acts to reduce the load current. This is most-usually done by installing capacitors close to the load, and is termed 'power-factor correction' or 'power-factor improvement'. Capacitors used in this way are rated in reactive volt amperes, rather than in microfarads.
