Misconceptions about Electricity and Magnetism

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There are lots of misconceptions about electricity and magnetism, perhaps because it is something you can't see directly.  You can observe its effects, such as watch an electric light bulb being lit, or a electric motor turn in response to the current flowing through the wires, but you can't see that current directly.  Indeed, it wasn't until the twentieth century that scientists figured out there is a discrete values of charge (which we now know corresponds to the charge on a single electron or proton).

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1.  A battery stores charge

A common misconception is that a battery holds charge.  After all, do we not "recharge" some batteries?

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In fact, a battery stores energy, generally in chemical form.  It doesn't hold charge.  After all, the electrons that most typically move in a circuit are found in all atoms.  Those substances that are conductive, simply have electrons that are loosely bound, are readily bumped along to other atoms.  Although in everyday speech we do say that we can "recharge" a battery, a more correct term would be raising the batteries chemical potential energy by forcing current "backwards" through it.

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When we use the battery; for example to light a flashlight, the chemical energy simply pushes the electrons around.  How much energy is added depends on the voltage of the battery.  Voltage is an expression of the Electric potential energy per unit charge.

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2.  The best conductor is gold

Gold is a good conductor, but certainly not the best.  The best conductors of both heat and electricity are silver, copper, and aluminum.  That said, gold is important because it doesn't react with oxygen readily so it doesn't corrode.  Thus audio connectors and some others are sometimes gold plated to protect the copper interior, which would otherwise corrode if exposed to the air.  Since the layer of gold needed is so thin, it doesn't impede the flow of electrical current significantly.   The resistance of wire can be measured with an ordinary multimeter, but because it is such a good conductor, you may need a long roll of it!  A simpler way is to Google it!

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3.   Current is the flow of electrons

Not necessarily.  electrons are certainly what flows in conductive metals, like copper, but protons or positively or negatively charged particles can move too, resulting in electrical current flow.  This might happen, for example, when current flows through a salt-water solution. Try it!

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4.  Electrical current flows at the speed of light.

When, for example, you switch on a light, electrons don't have to travel from the switch to the lightbulb before it lights.  Electrons, donated by the conductive material in the wire (such as Copper) are already present in large quantity throughout the wire.  The electric potential gradient changes abruptly, causing all these electrons to start moving along the wire.  (Imagine a hose full of water, then you turn on the tap.)  The electrons already present in the lightbulb start to move and it lights.  Since the electrons have little mass (much less than water molecules), the flow does start nearly instantly, but it takes much longer for any one electron to move very far along the wire.

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