Janice VanCleave's Physics for Every Kid. Janice VanCleave

      1 Fold the paper in half three times, once from top to bottom, and then from side to side, and last fold along a diagonal line so that the top folded edge meets the side fold as shown in Figure 1.FIG 1

      2 Draw five curved lines on the top layer of the folded paper.

      3 Cut along each of the five curved lines. Keep the three indicated sections as shown in Figure 2.FIG 2

      4 Unfold the three sections; write “6p+” and “6n” in the circle, which represents the six protons and six neutrons in the nucleus of the atom.

      5 In the smaller ring, draw two electrons (e−) on opposite sides, and in the largest ring, draw four electrons (e−) randomly spaced and as far apart as possible.

      6 Connect the three parts by taping the string to each as shown in Figure 3. Secure the end of the string to a surface so that the atom model can hang freely.

FIG 3

What Happened?

      This Bohr model is of the element carbon (C). The carbon atom model is neutral because it has six positively charged protons (p⁺) in its nucleus and six negatively charged electrons (e⁻) in the rings, which represent energy levels. In the Bohr model, atoms may hold up to two electrons in the first ring and up to eight electrons in the second ring. Since there are only a total of six electrons in a neutral atom of carbon, two electrons are in the first energy level and the remaining four electrons spread out in the second energy level, which is the outer ring. The electrons in the outer energy level of an atom are called valence electrons. The atom model of carbon has an overall charge of zero; thus, it is a neutral atom.

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.