Electronics Engineering

I think your question could be rephrased as:

"When viscous friction increases, why does currentdecrease?". Though the latter is not directly dependent on the former, or vice versa, in most motors this is the case. To understand exactly why this happens we need to look into the constructional features of a motor.

All motors have a rotor (the spinning part) and a stator (the stationary part). In linear motors the part the slides along can be thought of as the 'rotor', and the non-moving base, as the 'stator'. The motor spins by causing like poles on the stator and rotor to oppose each other (different motors - AC, DC, brushless - do this in different ways). Read up about this on Wikipedia, HowStuffWorks, or just Google around. For maximum efficiency it is desirable to build the rotor and stator in such a way that there is very little space between the two. This allows a high degree of magnetic flux linkage/concentration between the rotor and stator. Between the rotor and stator is a small air gap. Air, like all fluids, has viscosity (a sort of 'stickyness', if you will). Viscous force appears between two sliding objects which have a liquid in between them. The closer the sliding surfaces, the greater is the viscous force. Viscous force also depends on the area of the surfaces, their relative velocity, and the liquid's properties. For a detailed derivation please refer to any text on fluid dynamics.

Another important motor characteristic is back EMF (BEMF), which is induced in motor coils due to magnetic interaction. The faster a rotor spins, the greater the magnitude od back EMF. Back EMF, as its name suggests, has a polarity opposite to the applied (battery/power source) EMF. It is the back EMF which causes a reduction in motor current, since it partially cancels out the applied EMF : (Applied EMF-Back EMF)=(Effective EMF). Since the coils in the motor have unchanging resistance, a lower apparent EMF imples lower current.

Now let us link these two phenomena:

low speed-->low BEMF-->high current

also;

low speed-->low viscous friction

but:

higher speed-->higher BEMF-->lower current

and:

higher speed-->higher viscous friction

I hope this clears things up.

Rohit de Sa,

Engineer,

Mercedes-Benz,

INDIA

The biggest difference is the types of transistors used: TTL (transistor transistor logic) uses bipolar junction transistors, MOS (metal oxide semiconductor) uses metal oxide semiconductor field effect transistors.

For a very long time TTL operated at much higher speeds than MOS logic, but also used much more power. However several improvements in MOS over time eventually allowed it to operate at higher speeds than TTL could do without consuming so much power that it could not be properly cooled.

The actual circuits used to construct logic gates is very different, but these details cannot be addressed on this site.

Because it uses N-type and P-type semiconductor, usually silicon.

The construction will either be NPN or PNP, with the different types in a "sandwich" construction.

Relation is

F=pi*i*L*sin theta

But T= r*f

so T= pi*i*r*L*sin theta

pi(flux) and i (current) are changeable while all others are constant.

so

T= k pi * i

Dc servomotor Under Feild Control:

** Armature Current is Kept Constant

** Flux can be varied

The armature current can be kept constant by applying a constant current source at armature winding of DC servoMotor

Torque generated by the dc servo motor is controlled by feild current..

This mode of operation is called Feild Control

Circuit boards do not have to be assembled in a germ free environment.

You may be thinking of the manufacture of integrated circuits, which must be processed in a "clean room". In general "clean rooms" have only had to be dust free, not germ free. However as feature size keeps reducing on integrated circuits eventually the feature size will get smaller than the size of germs, at which point "clean rooms" will need to be germ free.

I once heard a story about a special type of vacuum tube that a company was manufacturing many years ago. After the old employee that was in charge of that production line retired. suddenly they could not make these tubes work anymore and the line shutdown. So they brought the employee back (figuring something was not properly documented in the procedure) and had him show them what he did to make one of these tubes and that tube worked perfectly. For a while they were baffled as he had done nothing different than what the procedure said, until they realized he chewed tobacco and always had residue on his hands. Examining the tubes he made and the tubes others made they found tobacco mosaic virus inside the tubes he made. When they started adding a tiny amount of tobacco mosaic virus to each tube before sealing it up, every tube they made worked perfectly from then on!

There has been some speculation that someday genetically engineered viruses will be used to "grow" the features on integrated circuits when they get too small for current methods to work anymore.

Number of turns

I assume that you have a phasor diagram of a transformer, and wish to identify the primary phasors and the secondary phasors?

For a three-phase transformer, this is fairly straightforward, provided the usual procedure for drawing a phasor diagram has been followed. Whenever you start to draw anysort of phasor diagram, you usually start by selecting a phasor of reference and draw that in the horizontal positive direction. For a three-phase transformer, the phasor of reference is usually the primary phase voltage A (or however else it is identified: R, red, or whatever). The remainder of the primary phase voltages are then drawn, enabling the primary line voltages to be constructed (which, in the case of a primary delta are the same as the primary phase voltages!). So if you can identify the phasor of reference, then you have identified the primary-winding phasor diagram. As the primary and secondary voltages are not usually drawn to scale, relative to each other, you can't assume a turns ratio from the phasor diagram. The labelling might also help, as high-voltage phase and line voltages are identified by upper-case letters, while low-voltage phase and line voltages are identified using lower-case letters -but, remember, these identify high- and low-voltages, not which is primary and which is secondary (primary winding is connected to supply/secondary winding is connected to load).

For single-phase transformer, the phasor of reference is the flux set up in the magnetic circuit, and voltages/current phasors are drawn relative to this. In this case, the primary line and induced voltages are usually identified as V1 and E1, and the secondary induced voltage as E2 (sometimes, the Es and Vs are interchanged). Again, the lengths of the primary and secondary voltages are not necessarily to scale relative to each other.

I don't know in detail why it happens, but your question is what happens. This is what happened to me. I failed to notice that a 22,000µF TOSIN power cap (that's quite a large, powerful and expensive Aluminium electrolytic can) was the wrong way round in circuit. The 500W transformer powering it (via a 25A rectifier) started buzzing on switch-on and during the time it took for me to get my multimeter on and measuring the outputs, both the transformer and the cap seemed to be getting quite hot, so I switched off the power.

In spite of the power being off, the cap started to bulge, most obviously at the end with the connections. It continued to be quite hot and bulged further until there was a mighty bang, the end of the can shot off and some evil-smelling brown fluid exploded all over my kitchen (range of about 10 feet). I take away the lesson that paying closer attention to polarity is probably a good idea.

Read more: If_you_connect_electrolitic_capacitor_with_oposite_polarity_what_happens

Georg Ohm first discovered his law empirically. Later he generalized it significantly and formalized it better. It seems that it got a rather cold welcome, which caused his withdrawal from the Academic world for six years. This wrong was later corrected, when he got the Copley medal. More about this is in the link about Georg Ohm. The well known law of the mathematical equation that describes the relationship

V = I * R

was later called "Ohm's law" to remember Georg Ohm. Ohm's own idea was more another equation:

Resistance R = rho * length / area.