Author: Lou Bloomfield

Is not the current used in Europe direct current? If so, do they use transformers or do their lines get very hot? Why do our appliances not work there?

Europe uses alternating current, just as we do, however some of the characteristics of that current are slightly different. First, Europe uses 50 cycle-per-second current, meaning that current there reverses directions 100 times per second. That’s somewhat slower than in the U.S., where current reverses 120 times per second (60 full cycles of reversal each second or 60 Hz). Second, their standard voltage is 230 volts, rather than the 120 volts used in the U.S.

While some of our appliances won’t work in Europe because of the change in cycles-per-second, the biggest problem is with the increase in voltage. The charges entering a U.S. appliance in Europe carry about twice the energy per change (i.e. twice the voltage) and this increased “pressure” causes about twice the number of charges per second (i.e. twice the current) to flow through the appliance. With twice the current flowing through the appliance and twice as much voltage being lost by this current as it flows through the appliance, the appliance is receiving about four times its intended power. It will probably burn up.

How come the flashlight works when you switch the batteries but my walkman or gameboy doesn’t?

The bulb in a battery doesn’t care which way current flows through it. The metal has no asymmetry that would treat left-moving charges differently from right-moving charges. That’s not true of the transistors in a walkman or gameboy. They contain specialized pieces of semiconductor that will only allow positive charges to move in one direction, not the other. When you put the batteries in backward and try to propel current backward through its parts, the current won’t flow and nothing happens.

Why are batteries so expensive?

They contain highly purified and refined chemicals and are actually marvels of engineering. It’s more surprising to me that they are so cheap, given how complicated they are to make.

If only electrons move around, why do you keep using positive charges in the demos?

It’s useful to describe moving electric charges as a current and for that current to flow in the direction that the charges are moving. Suppose that we define current as flowing in the direction that electrons take and look at the result of letting this current of electrons flow into a charge storage device. We would find that as this current flowed into the storage device, the amount of charge (i.e. positive) charge in that device would decrease! How awkward! You’re “pouring” something into a container and the contents of that container are decreasing! So we define current as pointing in the direction of positive charge movement or in the direction opposite negative charge movement. That way, as current flows into a storage device, the charge in that device increases!

How are you “shocked”?

Your body is similar to salt water and is thus a reasonably good conductor of electricity. Once current penetrates your skin (which is insulating), it flows easily through you. At high currents, this electricity can deposit enough energy in you to cause heating and thermal damage. But at lower currents, it can interfere with normal electrochemical and neural process so that your muscles and nerves don’t work right. It takes about 0.030 amperes of current to cause serious problems for your heart, so that currents of that size can be fatal.