May 12th - Magnets

Class started with the students discussing what they already know about magnets. We also went over the idea that magnets can attract or repel each other, just like electrical charges and the subatomic particles. In magnets, opposite poles (North and South) attract while like poles repel.

Close Encounters Lab – Each student was given two balloons, a marker, and some string. The students blew up each balloon then tied a piece of string to the end of each one. They labeled one balloon “A” and the other “B.” The free ends of each string was then taped in an open door frame.

The students charged Balloon A first and then observed the balloons. They then charged both balloons and observed.

We got really good results with the two charged balloons and were able to see them repel each other. We really didn’t see Balloon A attract Balloon B in the first part of the experiment but the students did understand this was supposed to happen.

Fun Fact – Magnets got their name from the region of Magnesia, which is now part of modern-day Greece. The first naturally occurring magnetic rocks, or lodestones, were found in that area almost 3,000 years ago. A lodestone is composed of an iron-based material called magnetite.

Iron from Cereal Lab – Prior to starting this lab we spent a few minutes discussing iron in foods. I asked the students if they knew reasons why humans need to consume iron and we spoke a little about the functions of iron and sources of iron.

Iron primarily functions as an oxygen carrier in the blood. It also assists with the immune system, cognitive development, temperature regulation, and energy metabolism.

Each student had a bowl of Corn Flakes that we added water to. We started out using a fork to make the cereal mushy but decided a blender would do a better job. Once the cereal was soggy, the students stirred a magnet through the cereal and then wiped it on a paper towel. We were able to find some small amounts of iron (it looks like black fuzz).

A few weeks ago, we went over Coulomb’s Law. This law states that the attraction or repulsion of two electrical forces becomes greater as the two charged objects get closer together. This same effect can be demonstrated with magnets. We used two bar magnets and found that as they were moved closer together, the attraction or repulsion became stronger.

Magnetic Domains – Magnetic materials contain magnetic domains. These are clusters of atoms that behave like tiny magnets. Objects are not magnetic when the magnetic domains are randomly arranged. However, if they do all line up, the object takes on magnetic properties. This explains how a nail or paper clip can become magnetized.

Permanent and Temporary Magnets – Some metals are permanent magnets due to the fact that their magnetic domains are permanently lined up. Fridge magnets and the magnets we had in class (horseshoe magnets, bar magnets, ring magnets) are all examples of permanent magnets.

Temporary magnets are metals that can be made into a magnet by lining up the magnetic domains. These include iron and nickel. Rubbing a paper clip or nail on a magnet will cause the magnetic domains to line up, creating a temporary magnet. An electromagnet is another example of a temporary magnet.

Suspended Airplane Lab – The students each created a small “wing” by folding up a piece of crepe paper. They inserted a pin through the center of the paper wing and then tied a piece of sewing thread to the head of the pin.

Each student placed a bar magnet on the edge of the table and then held the wing out in front of the magnet. The students observed as the wing was attracted to the magnet.

The magnetic field surrounding the magnet exerted the attracting force on the pin/wing. The pin and magnet both have magnetic properties. The two objects pulled on each other with enough force to overcome gravity, allowing the wing to remain suspended in the air.

Compasses and Earth’s Magnetic Field – The students all know Earth has a North Pole and South Pole. We are able to use compasses because the Earth acts like a giant bar magnet. The needle of the compass aligns with Earth’s magnetic field. The needle will point in a direction that lies along the magnetic field line at that point.

An interesting fact about Earth’s poles: Earth’s North Pole is actually at the south end of its magnetic field while its South Pole is at the north end of its magnetic field.

Swinger Lab – Each student was given a compass, a piece of sewing thread, a small paper clip, a ruler, some tape, a heavy book, and a magnet. They taped one end of the thread to the paper clip and then taped the other end to the ruler. The students then placed the ruler inside the book and placed the book on the edge of the table. They magnetized the paper clip by holding it on the bar magnet for several seconds. The students removed the paper clip from the magnet then let the clip swing freely. The compasses were placed on the table next to the book and the students observed the movement of the compass needle and where it stopped. The compasses showed that the paper clip pointed North-South once it stopped swinging.

The north poles of all magnets are attracted to the Earth’s north magnetic pole. Magnets are all north-seeking poles. As long as the paper clip is magnetized (its magnetic domains are lined up in a north-south direction), one end will point toward Earth’s magnetic north pole.

Electromagnet Lab – We attempted to make electromagnets using both insulated wire and bare copper wire. We didn’t have any luck with the insulated wire and only one student was able to get the electromagnet with the copper wire to work.

For this, the students wrapped the wire around a nail. They attached the free ends of the wire to a D-cell battery in a battery holder (one end to each battery terminal). They then tried to use the electromagnet to attract paper clips.

The Direct Current running through the battery should have caused the magnetic domains within the nail to line up causing it to become magnetic.

This is an easy one to try at home. Experiment with different types of wire or different nails. You can use electrical tape to attach the wires to the battery terminals.

Uses of electromagnets – Electromagnets are used in motors, CDs, computer hard drives, and alarms. I showed the class a transparency with a diagram of an alarm bell and asked them to locate the electromagnet. We also discussed how the electromagnet causes the alarm’s hammer to vibrate and create the alarm’s sound.

We finished up class by using magnets to move iron filings. The iron filings were attracted to the magnet that was moved over or under the plate the filings were on. The students were able to make patterns and also observed the filings “jump” up to stick onto the magnets. The filings are pulled toward the magnet when they enter the magnet’s magnetic field.

Next week:

Next week will be our last class session for the year. We'll study balance and flight. The students will review center of gravity (a topic we covered back at the beginning of the school year). We'll also learn about lift, thrust, and drag and how these forces, along with gravity, affect planes. 

References:

The labs "Close Encounters," "Swinger," and "Suspended Airplane" are all 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.

I found the "Iron from Breakfast Cereal" lab on this website: http://chemistry.about.com/cs/howtos/ht/ironfromcereal.htm

The idea to make electromagnets came from a Lakeshore Learning Materials kit on Electricity.

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