Month: December 1969

Can you explain power surges?

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Can you explain power surges?

Sometimes lightning strikes a power line and deposits a large amount of charge on it. This charge has considerable electrostatic potential energy so its voltage is very large (a large positive voltage if the lightning carried positive charge, a large negative voltage if the lightning carried negative charge). A the charge flows outward along the wires, it raises the local voltages of the wires. This sudden, brief increase in the local voltages is what you mean by a power surge. Many devices (e.g. computers and televisions) can be damaged by such a surge in voltage. Even a light bulb can be damaged because the extra voltage pushes too much current through the filament and can burn it out.

What happens when a battery dies?

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What happens when a battery dies?

A battery uses its chemical potential energy to pump electric charges from its negative terminal to its positive terminal. Eventually it runs out of chemical potential energy. In an alkaline battery, the chemical potential energy is mostly contained in zinc powder and this powder oxidizes as the battery operates; in effect, it burns up in a very controlled manner. By the time the battery is dead, there just isn’t much pure zinc metal left.

What exactly are fuses and why do people change them or blame them if something …

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What exactly are fuses and why do people change them or blame them if something short circuits?

A fuse is a weak link inserted into a circuit to break the circuit if too much current flows through it. The electric resistance of the fuse is large so that the current deposits a fair amount of thermal energy into it as it passes through. When the current exceeds the designated amount, the fuse melts and burns out. A short circuit usually blows out the fuse because it causes an enormous increase in the current flowing through the circuit. When that happens in your house, you should be thankful for the fuse because it saved you from the fire that might occur if it weren’t there. You sure don’t want the wires in your wall to melt and burn out because they might take the whole building with them. A circuit breaker is just an electromagnetic variation on the fuse. As the current through the circuit break increases, an electromagnet inside the circuit breaker becomes stronger and stronger until it eventually flips a switch that opens the circuit.

If you keep batteries in your car-where it gets really hot on a summer day-will …

Lou Bloomfield Leave a comment

If you keep batteries in your car-where it gets really hot on a summer day-will the batteries “die” faster? (I got brand new batteries and have them in a flashlight in my car and they are almost dead, yet I never really used the flashlight but for a couple of minute.)

Yes. Thermal energy spoils everything and the hotter you heat an object, the more thermal energy it contains. Keeping batteries or photographic film cool preserves them against aging.

How do collisions with tungsten atoms in the filament of a flashlight convert th…

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How do collisions with tungsten atoms in the filament of a flashlight convert the current’s electrostatic and kinetic energies into thermal energy?

When the electrons moving through the tungsten filament collide with the tungsten atoms, they do work on those tungsten atoms. Although the atoms are very massive and the electrons bounce off of them like Ping-Pong balls from bowling balls, the atoms do jiggle about after being struck. Bombarded by a steady stream of electrons, the atoms in the tungsten begin to vibrate harder and harder and soon become white hot. The electrons leave the tungsten filament with relatively little energy left-they use almost all of their kinetic and electrostatic potential energies to get through this gauntlet of tungsten atoms.

How can a battery lose energy when it’s not being used (like when it sits in a f…

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How can a battery lose energy when it’s not being used (like when it sits in a flashlight that’s not turned on for months or years)?

The battery maintains a steady positive charge on its positive terminal and a negative charge on its negative terminal, month after month. These opposite charges attract one another and they do manage to get back together occasionally. They usually travel right through the battery itself, assisted by thermal energy. When that happens, the battery has to pump additional charge from the negative terminal to the positive terminal to make up for the lost charge and consumes a little more of its chemical potential energy. You can slow down this aging process by refrigerating the batteries. With less thermal energy available, the accidental movements of charge through the battery become less frequent.

What materials are magnets made of?

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What materials are magnets made of?

They are mostly iron, cobalt, or nickel, which are intrinsically magnetic metals. But to help them retain their magnetic alignments, permanent magnets have other elements in them, too. Iron is magnetic at the microscopic scale, but that magnetism is broken up into lots of tiny regions that all point in random directions. To make a whole piece of iron magnetic, something must help those tiny regions stay pointing in the same direction. The good permanent magnets have structures that keep all the tiny regions pointing in one direction.

What is the difference between fields and charges (magnetic and electric)?

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What is the difference between fields and charges (magnetic and electric)?

Electric charges themselves push and pull on one another via electrostatic forces. Magnetic poles push and pull on one another via magnetostatic forces. We can also think of the forces that various electric charges exert on one charge that you’re hold as being caused by some property of the space at which that one charge is located. We call that property of space an electric field and say that the charge is being pushed on by the electric field. We could do the same with magnetic poles and a magnetic field. But these two fields are more than just a useful fiction. The fields themselves really do exist. You can see that whenever moving electric charge creates a magnetic field or when a moving magnetic pole creates an electric field. Light consists only of electric and magnetic fields.

What is the difference between current and voltage?

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What is the difference between current and voltage?

Current measures the amount of (positive) charge passing a point each second. If many charges pass by in a short time, the current is large. If few charges pass by in a long time, the current is small. Voltage measures the energy per charge. If a small number of (positive) charges carry lots of energy with them (either in their motion as kinetic energy or as electrostatic potential energy), their voltage is high. If a large number of charges carry little energy with them, their voltage is low.

What is the dangerous part of electricity: charge, current, voltage, or what?

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What is the dangerous part of electricity: charge, current, voltage, or what?

Current is ultimately the killer. A current of about 30 milliamperes is potentially lethal when applied across your chest. But your body is relatively insulating, so sending that much current through your chest isn’t easy. That’s where voltage comes in. The higher the voltage on a wire, the more energy each charge on the wire has and the more likely that it will be able to pierce through your skin and travel through your body. Thus it’s a combination of voltage and current that is dangerous. Current kills, but it needs voltage to propel it through your skin.