May 5th - Electricity II (Circuits)

We started our second electricity class by setting up solar cookers. We also spent a bit of time talking about how solar power works and the benefits of solar power.

Here's a link with directions to make a solar cooker. It's really easy and they really do work! :) Be sure to check it every 15-20 minutes so you can keep it in the sun. I think we would have had better results if we had checked ours.
We used the solar cooker to make s'mores but we finished toasting the marshmallows a bit using the flame from a candle.

As predicted, the smaller box made a more efficient solar cooker.

Gooey marshmallow fresh from the solar cooker!

Finishing the "toasting" process.

Yum!

Voltage - A volt is the measure of the difference in electrical charge across two points. I used a battery as an easy example. The students knew about the two battery terminals (positive and negative). In a battery, the voltage is the measure of the difference of charge across these two terminals. We looked at several types of batteries (D-cell, AA, AAA, 9 volt, etc.) and found the voltage for each one.

Current - We went back over Alternating Current (powers plug-in devices) and Direct Current (found in batteries). If you switch on a battery-powered flashlight, the terminals of the battery are connected through the light bulb. Electrons move through the bulb from the negative terminal to the positive terminal. When these charges are accelerated, a current is produced. Current, then, is the rate at which charges move through a conductor. Current is measured in amperes or amps.

Potato Circuit lab - We set this up at the beginning of class since it takes an hour to work. This lab required half of a potato, 2 pennies, a D-cell battery, 2 paper clips, masking tape, and a push pin. The students folded a piece of aluminum foil to create a long thin strip. They then cut this in half to make two thin strips. These strips became "wires." They cleaned the pennies with a little steel wool and then wrapped one end of each piece of foil around each of the pennies and used a paper clip to keep the foil in place. They stuck the edge of each penny into their potato half so the foil wire was on the outside of the potato. The students then used masking tape to attach the free end of the foil to the battery (one piece to each terminal). The push pin was inserted in the potato to help the students remember which penny was attached to the positive terminal of the battery. Once this is set up, leave the whole thing for one hour.

We removed the pennies at the end of class and found that the pennies that were attached to the positive terminal of the battery had left a green mark on the potato.
The copper in the pennies that were connected to the positive terminal took on a positive charge. These positive penny particles combine with negative particles in the potato to create a green copper compound.

The penny that was connected to the positive terminal left the green mark at the bottom of this potato.

Circuit - A fancy definition for a circuit is "a set of electrical components connected such that they provide one or more complete paths for the movement of charges." So, a circuit is a complete path that connects charges and allows them to be conducted.

An example of a basic circuit would be a battery, some wire, and a light bulb. If you connect them to create a complete path, the light bulb will illuminate.
When an electric current can travel through an entire circuit, the circuit is a closed circuit. If there are places where the electricity cannot pass or cross, the circuit is an open circuit.

Simple Circuits lab - Each student was given three pieces of wire, a lightbulb and bulb holder, a D-cell battery, and a battery holder. They then looked at the circuits pictured below and predicted which ones would allow the bulb to light up. The students then set up each of the five circuits and observed what happened.

Series Circuits - These have a single path for the current to flow. If one wire or connection in a series circuit is blocked or cut, the entire circuit is opened and it stops carrying the electrical current.
An example of a series circuit are the older holiday lights. If one bulb burned out or became loose or disconnected, the entire string of lights stopped working.

Parallel Circuits - These have multiple paths for current to flow. The electric current can follow two or more paths to form a circuit with a power source.
Newer strings of lights are an example of parallel circuits. Each bulb has its own complete/closed circuit connecting it to a power source. The lights continue to work even if one bulb burns out.

Parallel and Series Circuits lab - For this lab, the students predicted how series and parallel circuits would behave if one of the two light bulbs in each circuit was disconnected.
The students were given two bulbs and bulb holders, four pieces of wire, a D-cell battery, and a battery holder. They set up the series and parallel circuits as shown below and then unscrewed one bulb from each. We then observed what happened and discussed the results.

Switches - A light switch is probably the thing most people think of when they think of a switch. Switches can be found in all sorts of electrical appliances and machines to make them turn on or off. A switch is a gap in a circuit that can be opened or closed. When the switch is closed, the circuit is closed so this is the switch's "on" position. The "off" position opens the switch and the circuit.

Switching On and Off lab - The students set up a circuit using a bulb and bulb holder, a D-cell battery and a battery holder, a switch, and some wires. They then used the switch to open and close the circuit and observed what happened to the light bulb.
They also tried setting up other circuits with the switch by adding bulbs and batteries.

The students finished up class by checking on the solar cookers and enjoying s'mores.

To look forward to on May 12th:
We'll be studying magnets! We will experiment with different types of magnets, try extracting iron from cereal, and we'll make an electromagnet.

References
The lab "Potato Circuit" is from Physics for Every Kid.

VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

The labs "Simple Circuits," "Parallel and Series Circuits," and "Switching On and Off" are from a Lakeshore Learning Materials kit on Electricity.

I found the Solar Cooker instructions on the PBS Kids website.

More information on solar energy and how solar power works:
Energy Kids (from the US Energy Information Administration)

Solar Energy!

More information on circuits:
NASA Science Files - Circuits