Tag: electric power distribution

Where does the exact reversal occur in an alternating current circuit (where doe…

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Where does the exact reversal occur in an alternating current circuit (where does the energy diminish completely and then turn the opposite way)?

The reversal of the current in an alternating current (AC) circuit occurs everywhere in the circuit at once. The whole current gradually slows to a stop and then heads backward. At the moment it comes to a complete stop, the electric power company isn’t supplying any power at all and the circuit isn’t consuming any. Because the power delivery pulses on and off in this manner, devices that operate on AC power are designed to store energy between reversals. Motors store their energy as rotational motion. Stereos store energy as separated electric charge in devices called capacitors, or as magnetic fields in devices called inductors.

If current times voltage equals power, this makes it seem that high current time…

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If current times voltage equals power, this makes it seem that high current times low voltage would equal low current times high voltage; but this is not true because of resistance. How is resistance taken into account in the current times voltage equal power equation?

Your first observation, that high current times low voltage would equal low current times high voltage is true; it means that electricity can deliver the same power in two different ways: as a large current of low energy charges or as a small current of high energy charges. That result is critical to the electrical power distribution system. The resistance problem is a side issue: it makes the delivery of power as a large current of low energy charges difficult. If you could get this current to peoples’ houses without wasting its power, there would be no problem, but that delivery isn’t easy. The wires waste lots of power when you try to deliver these large currents. So the electric power distribution system uses small currents of high-energy charges instead.

Why are there danger signs around high voltage equipment?

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Why are there danger signs around high voltage equipment?

Your body is a relatively good conductor of electricity and it is easily damaged by currents flowing through it. Your body uses electricity to control its functions and an unexpected current of as little as a few hundredths of an ampere can interrupt those functions. In particular, your heart can stop beating properly. Fortunately, your skin is a pretty good insulator so it is hard to get any current to flow through you. But high voltages can push current so hard that it punctures your skin and begins to flow through you. While the current is actually what injures you, the high voltage is what breaks down your protective skin and allows that current to flow through you.

In what circumstances is a step-down transformer more advantageous than a step-u…

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In what circumstances is a step-down transformer more advantageous than a step-up transformer and vice versa?

The transformer moves power from the primary circuit to the secondary circuit, almost without waste. The main reason for using a transformer is to change the relationship between voltage and current. Whenever you need a large current of low energy, low voltage charges, you probably want a step-down transformer. Whenever you need a small current of high energy, high voltage charges, you probably want a step-up transformer. I have already described the issues in power distribution, but transformers are used in many other devices. Step-down transformers are used to power small electronic devices instead of batteries (those little black boxes you plug into the wall socket contain transformers and some electronics to convert the resulting low voltage AC into low voltage DC). Step-up transformers are used in neon signs and bug-zappers.

Why do north and south poles on magnets change back and forth?

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Why do north and south poles on magnets change back and forth?

Only electromagnets can change back and forth and then only when they are connected to a supply of alternating current. A permanent magnet, such as that used to hold notes to a refrigerator, has permanent poles that do not change. But an AC powered electromagnet, such as that found in a transformer, does have poles that change back and forth.

Is it true that if you double the current through a wire then you double the vol…

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Is it true that if you double the current through a wire then you double the voltage loss and if you halve the current then you halve the voltage loss?

Yes. When you try to push current through a wire, the voltage drop across that wire (i.e. the energy lost by each charge passing through that wire) is proportional to the number of charges flowing through that wire each second (i.e. the current through the wire). If you double the number of charges flowing through the wire each second, then each charge will lose twice as much energy (the voltage drop across the wire will double). If you halve the number of charges flowing through the wire each second, then each charge will lose half as much energy (the voltage drop across the wire will halve).

Why does a high voltage transformer make ozone?

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Why does a high voltage transformer make ozone?

High voltages involve large accumulations of like electric charges. These charges repel one another ferociously and can leap off into the air near sharp points and edges. They produce sparks and corona discharges. While these discharges are useful in some devices (e.g. copiers and air cleaners), they tend to transfer energy to air molecules and can break up those air molecules. When normal oxygen molecules (which each contain 2 oxygen atoms) break up, the resulting oxygen atoms can stick to other oxygen molecules to form ozone molecules (which each contain 3 oxygen atoms). That is why you can often smell ozone near electrical discharges, high voltage power lines, and after thunderstorms.