Electronics Engineering

In a PN junction diode, the reverse current is due to the diffusive flow of minority electrons from the p-side to the n-side and the minority holes from the n-side to the p-side. Hence IS, reverse saturation current depends on the diffusion coefficient of electrons and holes. The minority carriers are thermally generated so the reverse saturation current is almost unaffected by the reverse bias but is highly sensitive to temperature changes. so , as the temperature increases the density of minority charge carriers increases creating a slight increase in the amount of IC.

so, the inference is reverse current is directly proportional to temperature

In the reverse biased condition the PN diode is least dependent on voltage till certain limit called breakdown voltage, till that voltage the increase in V is not actually increasing the current it is just increasing the heat at the junction which in turn raises the temperature and so the minority charge carriers.

But if the voltage increases the breakdown voltage the pn junction is lost and all the holes and electrons will start acting like charge carriers , such avalanche of charge carriers increases the current sharply to several hundred times. This phenomena is called as zener or avalanche breakdown

so if applied voltage less than breakdown voltage

no significant change in reverse current(only due to minority charge carriers)

and if applied voltage greater than breakdown voltage

the pn junction break and current increases sharply (both due to minority and majority charge carriers)

its 44000

Source:

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Electromagnetic waves, such as radio waves and light waves, travel in a vacuum at 300,000,000 meters per second so the wavelength of a radio wave at any particular frequency can be calculated by using the formula:

[Wavelength in meters (m)] =

300,000,000 / [Radio frequency in cycles per second (Hz)]

AM (Medium and long wave) broadcasts:
Frequencies: 300 to 3,000 kilohertz (KHz)
Wavelengths in air: 1,000 meters to 100 meters

FM (UHF radio and television broadcasts):
Frequencies: 300 to 3,000 megahertz (MHz)
Wavelengths in air: 100 centimeters to 10 centimeters

by using the step down transformer we can easily reduce the voltage.if we step down means the current(amps) icrease its vry useful for us

As transformers are a.c. machines, you cannot use a transformer for this purpose. You will need to create a voltage dividercircuit -essentially a pair of resistors, of appropriate value, connected in series across the supply.

A short circuit is one that is characterized by extremely low resistance. This will result in the extremely dramatic increase of current. High current will flow until a safety device opens the circuit, or the weakest link in it burns out. And one of the two usually occurs in a moment or two.

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Short Circuit happens when the cables of the electrical appliances are worn out or it's not connected properly,a short circuit may occure.A short circuit has a very low resistance that almost all electric current flow through it.It'll affect the operation of the electrical appliances.Owing to the heating effect,the excess electric current would produce a large amount of heat,wihout a fuse or a circuit breaker,a fire may be occured when there's a short circuit.

Reactive power is an odd topic in AC (Alternating Current) power systems, and it's usually explained with vector mathematics or phase-shift sinewave graphs. However, a non-math verbal explanation is possible.

Note that Reactive power only becomes important when an "electrical load" or a home appliance contains coils or capacitors. If the electrical load behaves purely as a resistor, (such as a heater or incandescent bulb for example,) then the device consumes "real power" only. Reactive power and "power factor" can be ignored, and it can be analysed using an AC version of Ohm's law.

Reactive power is simply this: when a coil or capacitor is connected to an AC power supply, the coil or capacitor stores electrical energy during one-fourth of an AC cycle. But then during the next quarter-cycle, the coil or capacitor dumps all the stored energy back into the distant AC power supply. Ideal coils and capacitors consume no electrical energy, yet they create a significant electric current. This is very different from a resistor which genuinely consumes electrical energy, and where the electrical energy flows continously in one direction; moving from source to load.

In other words, if your electrical appliance contains inductance or capacitance, then electrical energy will periodically return to the power plant, and it will flow back and forth across the power lines. This leads to an extra current in the power lines, a current which heats the power lines, but which isn't used to provide energy to the appliance. The coil or capacitor causes electrical energy to begin "sloshing" back and forth between the appliance and the distant AC generator. Electric companies must install heavier wires to tolerate the excess current, and they will charge extra for this "unused" energy.

This undesired "energy sloshing" effect can be eliminated. If an electrical load contains both a coil and capacitor, and if their resonant frequency is adjusted to exactly 60Hz, then the coil and capacitor like magic will begin to behave like a pure resistor. The "energy sloshing" still occurs, but now it's all happening between the coil and capacitor, and not in the AC power lines. So, if your appliance contains a large coil induction motor, you can make the motor behave as a pure resistor, and reduce the current in the power lines by connecting the right value of capacitance across the motor coil.

Why is reactive power so confusing? Well, the math is daunting if not entirely obscure. And the concept of "imaginary power" puts many people off. But this is not the only problem. Unfortunately most of us are taught in grade school that an electric current is a flow of energy, and that energy flows back and forth in AC power lines. This is completely wrong. In fact the energy flows constantly forward, going from source to load. It's only the charges of the metal wires which flow back and forth.

Imagine that we connect a battery to a light bulb. Electric charges already present inside the wires will begin to flow in the circle, and then electrical energy moves almost instantly to the light bulb. The charge flow is circular like a belt, but the energy flow is one-way. Now imagine that we suddenly reverse the connections to the battery. The voltage and current will reverse... but the energy still flows in the same direction as before. It still goes from battery to bulb. If we keep reversing the battery connections over and over, we'd have an AC system. So, in an AC system, only the voltage and current are "alternating," while the electrical energy flows one-way, going from source to load. Where AC resistive loads are concerned, electrical energy does not "alternate." To understand energy flow in AC systems, it's critically important that we understand the difference between charge flow (current, amperes) and energy flow (power, watts.)

What is imaginary power? Simple: it's the unused power which flows backwards and forwards in the power lines, going back and forth between the load's coil or capacitor and the distant AC generator. If your appliance was a pure capacitor or inductor, then it would consume no electrical energy at all, but instead all the flowing energy would take the form of "sloshing energy," and we'd call it "imaginary power." Of course it's not actually imaginary. Instead it's reflected by the load.

What is real power? Even more simple: it's the energy flow which goes continuously from the AC generator and into the appliance, without any of it returning back to the distant generator.

Finally, what is "apparent" power? It's just the combination of the above two ideas: it is the continous-forward-moving or "real" energy flow, combined with the sloshing or "imaginary" energy flow.

A tungsten filament does follow Ohm's Law at any instant of time. You may be confused in that the filament resistance changes from its "cold" state to its "hot" state. When cold the resistance is about 1/15 the resistance of what it is when the filament heats up, which happens very quickly. At any instant Ohm's Law holds. When the voltage is applied you have an initial current draw that exceeds the steady state current draw based on the change in resistance.

Ohm's Law either applies, or it does not. It cannot apply 'at an instant of time' -a change in current is either proportional to a change in voltage, or it isn't!

A tungsten filament does not obey Ohm's Law, because the current flowing through the filament does not increase in proportion to the applied voltage. This is because the resistance changes due to the filament's increasing temperature as the applied voltage increases. This is why Ohm's Law specifies that current is proportional to voltage, provided the temperature remains constant.

Although tungsten doesn't obey Ohm's Law, the so-called Ohm's Law equation applies whether a circuit obeys Ohm's Law or not. This is because the formula is really derived from the definition of the ohm, and not from Ohm's Law itself, which makes absolutely NO reference to resistance!

The simplest example of Ohm's Law is an old fashioned dimmer switch in your house. As you turn the dimmer switch up, the light gradually brightens until it reaches full intensity. Conversely, you can turn the dimmer switch down, and the light gradually darkens.

The dimmer switch is a variable resistor. That is, the electrical resistance of the dimmer switch changes as you rotate the knob. Ohm's Law tells us that the flow of current is directly proportional to the voltage, and inversely proportional to the resistance. Since the voltage across the switch doesn't change, the only thing that changes is the resistance when you turn the dimmer switch knob.

As you turn the dimmer switch down, you are actually increasing the resistance of the dimmer switch. The current is inversely proportional to the resistance, so as the resistance goes up, the current (flow of electricity) goes down, and the light gets darker. This is an example of Ohm's Law.

NOTE: This example applies to rheostat switches, and does not apply to modern current-clipping dimmer switches. Rheostat switches are seldom used now because they can overheat, but the illustration is still a useful example of Ohm's Law.

A more accurate answer is that silver is heavier than copper, softer, and has very similar conductivity. Silver is 10490 kg/m^3 while copper is only 8930 kg/m^3. Their bulk resistance is something on the order of 1.6 microOhm/cm for silver and 1.7 microOhm for copper.

Long story short, why would someone spend more money on a metal that doesn't hold up as well, is heavier and has slightly better conductive properties that most likely will never be used.