0
Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
Why do you put a diode across a relay coil?
If the current through a coil is interrupted, the coil generates a high voltage (such as in the old car ignition coils). The diode provides a path for the current to decay naturally, thus avoiding the high voltage.
How can a simple electromagnet be made?
first, you have to have a ferromagnetic core, like an iron bolt.
then, you wind a magnetic wire around it. the thicker the winding, the stronger the magnet.
the tips of the wire should be protruding so you can connect it to a source. skin the tips of the wire, too.
connect the wire to a dc source and you got an electromagnet.
What is maximum safe voltage for portable electrical tools?
There's no set answer to that, it's always a tradeoff between how well insulated the tool is, and what voltage it uses.
What are the 3 types of lever?
THREE CLASSES OF LEVER There are three classes of lever and each class has fulcrum, load and effort which together can move a heavy weight. CLASS 1 The workman uses a trolley to move the large packing case. The fulcrum is the wheel. CLASS 2The gardener uses a wheel barrow to lift tools and garden waste. The load is in the centre of the barrow CLASS 3 The fisherman catches the fish which becomes the load at the end of the lever.
What is a device that increase or decreases voltage in a power line?
A transformer. A small example is the coil in a motorcar. A transformer, in a power line, only changes voltage in one direction under normal usage. At distribution voltages, about 8360 VAC, the voltage is monitored by a regulator. A regulator either increases or decreases the voltage automatically to insure the desired voltage is steady. This regulated voltage is then fed to Transformers to provide customers with a regulated voltage at the desired voltage.
What engineering applications use second order derivatives?
Second order derivative is used in many fields of engineering. One of its application is used in solving problems related to dynamics of rigid bodies and in determination of forces and strength of materials.
What are the advantages of using fiber optic cable?
1. Immunity to Electromagnetic Interference
Although fiber optics can solve data communications problems, they are not needed everywhere. Most computer data goes over ordinary wires. Most data is sent over short distances at low speed. In ordinary environments, it is not practical to use fiber optics to transmit data between personal computers and printers as it's too costly. Electromagnetic Interference is a common type of noise that originates with one of the basic properties of electromagnetism. Magnetic field lines generate an electrical current as they cut across conductors. The flow of electrons in a conductor generates a magnetic field that changes with the current flow. Electromagnetic Interference does occur in coaxial cables, since current does cut across the conductor. Fiber optics are immune to this EMI since signals are transmitted as light instead of current. Thus, they can carry signals through places where EMI would block transmission.
2. Data Security
Magnetic fields and current induction work in two ways. They don't just generate noise in signal carrying conductors; they also let the information on the conductor to be leaked out. Fluctuations in the induced magnetic field outside a conductor carry the same information as the current passing through the conductor. Shielding the wire, as in coaxial cables can reduce the problem, but sometimes shielding can allow enough signal leak to allow tapping, which is exactly what we wouldn't want.
There are no radiated magnetic fields around optical fibers; the electromagnetic fields are confined within the fiber. That makes it impossible to tap the signal being transmitted through a fiber without cutting into the fiber. Since fiber optics do not radiate electromagnetic energy, emissions cannot be intercepted and physically tapping the fiber takes great skill to do undetected. Thus, the fiber is the most secure medium available for carrying sensitive data.
3. Non Conductive Cables
Metal cables can encounter other signal transmission problems because of subtle variations in electrical potential. Electronic designers assume that ground is a uniform potential. That is reasonable if ground is a single metal chassis, and it's not too bad if ground is a good conductor that extends through a small building. However, the nominal ground potential can differ by several volts if cables run between different buildings or sometimes even different parts of the same building.
Signal levels in semiconductor circuits are just a few volts, creating a problem known as ground loop. When the difference in ground potential at two ends of a wire gets comparable to the signal level, stray currents begin to cause noise. If the differences grow large enough, they can even damage components. Electric utilities have the biggest problems because their switching stations and power plants may have large potential differences.
A serious concern with outdoor cables in certain computer networks is that they can be hit by lightning, causing destruction to wires and other cables that are involved in the network. Certain computer companies are aware of this problem and trying to solve it by having protective devices for wire circuits to block current and voltage surges.
Any conductive cables can carry power surges or ground loops. Fiber optic cables can be made non-conductive by avoiding metal in their design. These kinds of cables are economical and standard for many indoor applications. Outdoor versions are more expensive since they require special strength members, but they can still be valuable in eliminating ground loops and protecting electronic equipment from surge damage.
4. Eliminating Spark Hazards
In some cases, transmitting signals electrically can be extremely dangerous. Most electric potentials create small sparks. The sparks ordinarily pose no danger, but can be really bad in a chemical plant or oil refinery where the air is contaminated with potentially explosive vapours. One tiny spark can create a big explosion. potential spark hazards seriously hinder data and communication in such facilities. Fiber optic cables do not produce sparks since they do not carry current.
5. Ease Of Installation
Increasing transmission capacity of wire cables generally makes them thicker and more rigid. Such thick cables can be difficult to install in existing buildings where they must go through walls and cable ducts. Fiber cables are easier to install since they are smaller and more flexible. They can also run along the same routes as electric cables without picking up excessive noise.
One way to simplify installation in existing buildings is to run cables through ventilation ducts. However, fire codes require that such plenum cables be made of costly fire retardant materials that emit little smoke. The advantage of fiber types is that they are smaller and hence require less of the costly fire retardant materials. The small size, lightweight and flexibility of fiber optic cables also make them easier to be used in temporary or portable installations.
6. High Bandwidth Over Long Distances
Fiber optics have a large capacity to carry high speed signals over longer distances without repeaters than other types of cables. The information carrying capacity increases with frequency. This however, doesn't mean that optical fiber has infinit bandwidth, but it's certainly greater than coaxial cables. Generally, coaxial cables have a bandwidth parameter of a few MHz/km, where else the fiber optic cable has a bandwidth of 400MHz/km. (These figures are just approximations and do vary from cable to cable!) This is an important factor that leads to the choice of fiber for data communications. Fiber can be added to a wire network so it can reach terminals outside its normal range.
The three main advantages are:
Speed - Fibre-optic cable is capable of transmitting data at a MUCH faster rate than copper cable.
Signal - Copper cable loses signal readily with length, and has to be boosted at regular intervals. The signal in Fibre-optic cable doesn't deteriorate nearly as much over distance and requires less boosting.
Capacity - Copper cable (using analogue signals) can only carry ONE signal at a time. Fibre-optic cable (using digital signals) can carry many data 'streams' as you just encode each stream so it gets to the right destination.
What is the difference between transistor and transformer?
A transistor in the right circuit, contributes a POWER GAIN by taking energy from an external power supply.
A transformer actually has losses but is primarily used for Impedance Matching. This is very useful in establishing the most efficient arrangements for transmitting power from the source to the load.
Impedance matching is an important function of all power transfer systems.
How does a capacitor store energy?
The energy stored in a capacitor is almost entirely in the electric field produced between the plates. It takes energy from a battery or some other power source to move electrons to one of the plates and away from the other. This makes one plate positively charged and the other negatively charged. Electric field is produced in proportion to the charge per unit area on a plate, and this electric field is said to originate on positive charges and terminate on negative charges.
Energy stored in electric fields is proportional to the square of the electric field strength and the volume of the field.
The energy is transferred from the power source to the electric field through the rearrangement of electrical charges.
What is tertiary winding of a transformer?
A third winding - primary, secondary, and tertiary. The third winding is typically sized much smaller than the primary and secondary, and is very often a lower voltage; it can be used for stabilization, removal of 3rd harmonics, power factor correction injection (lower voltage inductors are cheaper), and station service.
What would be the resistance of an ideal voltmeter?
The theoretical resistance (idea resistance) of an ammeter is zero. With a voltmeter, it's infinitely high.
In some analog meters the full scale deflection is produced by only about 50 microamps. Actually that does not change from ammeter to voltmeter, just the configuration of the meter's external "connection circuit"changes.
Simple ammeters are 'connected in series' devices. The resistance of such an ammeter must be kept very low because, if it were a high resistance, that would seriously limit the current allowed into the circuit and would impair the circuit's function.
Voltmeters are 'connected in parallel' devices. The theoretical resistance of a volt meter is very high, the higher the better. It is checking the potential between two points, so, to have the least effect on the circuit it is measuring, it must draw as little current as possible.
A generator transforms mechanical energy into electrical energy.
acceptor circuit is the circuit which accepts only one frequency and reject the others
What is the current in a 12volt circuit that has 9 ohms of resistance?
Ohm's Law: Current equals voltage divided by resistance
If the two 3 ohm resistors are in series, then 12 volts divided by 6 ohms is 2 amperes.
If the two 3 ohm resistors are in parallel, then 12 volts divided by 1.5 ohms is 8 amperes.
WARNING: In the first case, this is 24 watts or 12 watts per resistor. In the second case, this is 96 watts or 48 watts per resistor. Exercise great care if you intend to duplicate this in the lab, i.e. do not think for even a split second that a 1/4 watt resistor is going to be able to handle this power without burning up and causing a fire.
What is the voltage if the current is 0.4 and the resistance is 3?
If the current is 0.4 and the resistance is 3 the voltage is 1.2 V
Can a motor work as a generator?
Turn the shaft ;)
A brushed-commutator dc motor can be turned into a generator by connecting its shaft to another source of power to make it turn at the correct speed.
A diesel or gas engine - or another type of electric motor, such one that runs on 120V or 240V single phase ac - could be suitable.
The current of the earth fault.
is appox 1.7amp please verify this with book concepts of physics by h.c. verma
because i read it few year back and at present i don't have that book
A current that flows from phase conductors to earth or protective conductors etc from the point of an insulation breakdown.
Can you run 480v 60hz motor on 440v 50hz system?
As long as they're the same voltage, yes it will, but probably not for long. A lot depends on what type of appliance you're using. For instance, if it's an electric stove, you'd probably be OK, but if it has a clock, expect it to run slow. And even that too, dependfs on what type of electric stove it is. The problem is that at the lower frequency, the device has to draw more power in able to do the same amount of work that it would at 60 Hz. Because of that, some motors, electronically controlled devices and the like, tend to overheat as a result. For a window fan, it's probably no big problem (although I'd keep an eye on it until I knew for sure) but for something that's `frequency dependent', like a refrigerator compressor, I'd think you'd just be asking for problems. Usually during the day, voltages and frequency of the U.S. system varies in both frequency and voltage. A `brown-out' usually happens when the voltage falls below 80 volts, as compared to the nominal 117 volts. But too, so does the frequency. Tis is mainly because of industrial usage during the day, along with air conditioners and the like. Late at night though, it's usually closest to where it's supposed to be. Does it work? Will it work? Yes. The question is: For how long.
What is the significance of ohm's law?
Answer: Ohm's law is the most basic and most useful electrical equation. It explains the relationship between voltage (E) measured in volts, current (I) measured in amps, and resistance (R) measured in ohms. Without going into too much detail, Ohm's law plays a key PC role in Parallel versus Series Wiring. Parallel wiring is connecting components to a source so that they share the same voltage while Series wiring is connecting components to a source so that they share the same current.
What are the three main function of the multimeter?
A typical multimeter can measure:
* AC & DC voltage (volt)
* AC & DC current (amp) * resistance (ohm)
Can the transformer work on direct current?
No. It need an alternating current to induce current into the secondary winding. It needs an expanding and collapsing magnetic field to bring about this induction. The only time you get this phenomena in DC is when the current is turned on and again when the current is turned off.
What is the peak value of a 115V rms sin wave?
RMS*SQRT(2)=V(peak)
or
115V*1.414= 162.63V(peak)
Source: What_is_the_conversion_for_rms_voltage_to_peak_to_peak_voltage
Is mutual flux in transformer constant for all loads?
The flux is set by the voltage applied to the transformer. In most applications, the voltage is constant, and therefore the flux is constant also.
Why the core of the transformer is made laminated?
The alternating current flowing through transformer windings changes its polarity with each reversal of the current polarity, simultaneously changing the orientation of the induced magnetic poles within the core material. This constant fluctuation creates heat and other undesirable effects within the transformer, reducing its efficiency. Transformer cores are made of laminated steel or iron to minimize the effects of this electromagnetic phenomenon, which is known as hysteresis.
AnswerThe alternating current flowing through a transformer's primary winding induces voltages into the transformer's core, as well as in the secondary winding. The voltages induced into the core create currents that circulate within the core -these are called 'eddy currents'. Laminating the core reduces the effective cross-sectional areas through which the eddy currents circulate, thus increasing the resistance to those currents, and reducing the associated losses (eddy-current losses). In addition to this, laminations allow the transformer core to be assembled much more easily than using solid cores.