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11 Electric Current

An electric current is the movement of electrons. The faster the electrons move, the more kinetic energy they have. Kinetic energy of moving electrons can be called electrical energy. The strength of the current, or flow rate, is a measurement of the number of electrons moving past a point each second and is measured in amperes (A). One ampere is equal to 6.24 quintillion (=6.24 million million million) electrons each second. You can model the flow rate of current electricity using grains of sand. Just as the flow rate of an electric current is measured in electrons per second, the flow rate of sand can be measured in the number of ounces of sand that flows per second.

See for Yourself

Materials

 pencil

 paper cup, 7 oz (210 mL)

 masking tape

 small grain sand

 ruler

 small bowl

 timer

 helper

What to Do

Note: This experiment works best on a dry day, because moist sand tends to stick together when the weather is humid.

1 Use the pencil to punch a hole in the center of the paper cup's bottom. The hole should equal the circumference of the pencil

2 Place a piece of tape over the hole in the cup.

3 Fill the cup to the top with sand. Rub the edge of the ruler across the top of the cup to make sure the surface of the sand is level.

4 Hold the cup 6 inches (15 cm) above the bowl.

5 Ask your helper to start the timer as soon as you remove the tape from over the hole in the cup. Stop the timer the instant the sand stops flowing from the cup.FIG 1

6 Repeat the experiment four times, and then average the times taken from all the tests.

7 Calculate the flow rate of the sand using the following equation:

Note: The volume of the sand is equal to the volume of the cup used.

What Happened?

The flow of sand passing through the hole can be described as the volume measured in ounces (mL) of sand that passed a given point in one second. The flow rate of sand is not an exact model of the flow rate of electrons, but it does model measuring the flow rate of the material. The larger the hole in the cup, the greater will be the flow rate of sand. The same is true with an electric wire: the larger the diameter of the wire, the greater will be the current of electricity flowing through.