Electricity Workshop ©2008 ScienceScene Page 1
Table of Contents
I. Static Electricity
A. Teaching of Static Electricity
B. Wonderment of Producing Static Charge
1.Rubbing
a. The Fluttering Butterfly...... 5
b. The Static Mystery...... 6
2. Contact
a. Fickle Friends...... 7
b. The Repulsive Ball...... 8
3. Induction
a. Dancing Spheres in Captivity...... 9
b. The Attractive Yard Stick, Broom, and 2 X 4’s...... 10
C. Explanations - Developing A Model
1. How Do Materials Become Charged?...... 11
2. Using The Model To Illustrate the Static Charge?...... 12
3. Developing the Laws of Static Electricity
a. The Repulsive Golf Tube and Attractive Test Tubes...... 13
b. Sticky Tape Static Charges...... 14
4. The Electrostatic Series ...... 15
a. Where Should We Put Scotch Tape In The Series? ...... 16
b. Attractive Stuff...... 17
D. Applying the "Model" For Static Electricity
1. The Moving Soda Can(s)...... 18
2. Groovy Record...... 19
3. Electrophorus...... 20
4. Static Electric Doorbell ...... 21
5. Van De Graff Demo
II. Flowing or Current Electricity
A. Wonderment of Current Electricity ...... 22
B. Building The "Simply Super" Circuit Board...... 23
C. Parallel Circuits...... 24
D. Series Circuits...... 25
E. Combined Circuits...... 26
F. Conductors...... 27
G. Fuses...... 27
H. Diodes...... 27
I. Resistors...... 28
Static Electricity
A. Teaching of Static Electricity
Fundamental Forces and Static Electricity
All life depends upon energy, which allows us to interact with our environment. Energy is defined as the ability or capacity to do work. All energy originates from four fundamental forces: strong nuclear forces, weak nuclear forces, gravitational forces, and electromagnetic forces. We find that these fundamental forces act to produce common forms of energy in our environment such as thermal, light, sound, mechanical, electrical, magnetism, chemical, and nuclear. An investigation of electricity includes static electricity. Static electricity is found everywhere around us. Painting, printing, and copying industries use static electricity. Static electricity is found in our homes. Lightning is the result of static electricity discharging and can be quite harmful.
Goals to “Uncover”
a. The nature and occurrence of static electricity.
b. The production of static electricity by the action of friction.
c. Static electricity can be collected, but it is hard to hold on to.
d. Understand the atom through the use of models.
e. Water reduces or eliminates static electricity.
Background Concepts Concerning Static Electricity
Static electricity occurs when there is an excess of electrons in the material. In a material that is a poor conductor, the electrons are unable to move therefore the charges are unable to move in the material. That is, electrons can be grouped in one place and the atoms with fewer electrons in another place. The charge produced must be equal and opposite. Static electricity is produced in three ways:
a.friction • Objects can be charged by rubbing them together. As the two objects touch, one gives up loosely held outermost electrons to the other. Thus, the material that receives electrons becomes negatively charged and the material that loses electrons becomes positively charged. When you walk across a room on a rug on a cool dry day, you may gain a static electric charge by friction. The rubber soled shoes rub against the wool carpet and gain electrons from the carpet. When you reach for the metal door knob, these excess electrons are discharged to the knob, causing a shock.
b.contact• A material can be charged if electrons are transferred from one material to another by contact This generally happens when one material is charged and it touches either a neutral or oppositely charged material. If you have ever seen a person put his/her hand on a Van de Graaff generator, you have observed charging by contact.
c.induction •A material may be charged by induction when it is brought near a charged body. If the material is a conductor, it has electrons that are relatively free to move.
Difference between static electricity and current electricity; The only difference between static electricity and current electricity is that in current electricity the charges (electrons) move for a prolonged period of time. Current electricity requires a continuous source of electrons. In static electricity there is an excess of a charge on a material and that excess charge will flow to another charged material or to a neutral material. Once the excess electrons have been transferred, there is no flow of electricity.
The tenants of the atomic model related to Static Electricity are:
a.Atoms are made up of tiny electrically charged and non-electrically charged particles.
b. The nuclei of atoms are made up of protons and neutrons. Protons are positively charged. Neutrons are neutral.
c.Electrons are negatively charged and orbit around the positively charge nucleus.
d.The positive protons in the nucleus cancel out the orbiting negative electrons. Nuclear forces hold atoms together.
e.The protons and neutrons in the nucleus are “heavy” and stay together as a tight-knit group in the center of the atom.
f.The electrons of the atom are much “lighter” in mass than the nucleus. Electrons travel alone and far away from each other in separate orbits (as the planets do around the sun). The paths of the individual electrons do not meet because their like negative charges repel one another.
Electric charges can be positive or negative. A positive charge is caused when atoms lose electrons and has a force. The force makes it possible for paper to stick to a wall or for items that are electrically charged to “stick together.” A negative charge is caused when atoms gain electrons, or when electrons are knocked free of an atom and remain loose. The negative charge also has a force that causes it to push or pull, thus causing materials to “stick together.” A neutral material has an equal number of positive and negative electric charges, therefore does not have a force or charge.
Electron transfer occurs when two different dry materials are rubbed together.
a.The atoms of the two dry materials are jostled through the friction action of vigorous rubbing. The heat from friction and the collisions of electrons caused from jostling, cause the outer orbiting electrons to separate from their atoms.
b.One of the two materials will have temporarily lost electrons and will carry a positive charge. The other material will have temporarily gained electrons and carry a negative charge.
c. Rubbing two different, dry, “electrically neutral” materials together does not produce electric current. It merely creates a temporary imbalance in the number of electrons possessed by the atoms of each material.
Note: A law of static electricity, as in magnetism, like electrical charges repel and unlike electrical charges attract. Positive attracts negative. Positive repels positive. Negative repels negative.
Note: The study of static electricity reveals certain concepts about electricity. It is easy to collect on a dry day, but hard to hold on to. Moisture shortens the time span of a charge’s force. Moisture helps a charge neutralize itself. Only separated or “free” electric charges (+ or —) carry force. When an electron is no longer separated or “free” from its atom, it is neutral and carries no force (charge).
Conductors are materials that allow electric charges to pass and spread through them easily (like metal and water or moisture). Static electricity cannot accumulate and collect on things when electrons flow easily. If there is no conduction path to remove a charge, then static electricity stays at rest and a static force (charge) results.
Induction of a static charge can occur on a conductor by bringing an object with a charge on it near the conductor. Because opposites attract, one charge on the normally neutral conductor is attracted to the charged object, and the other charges move as far away as possible.
Insulators are materials that do not allow electric charges to pass through them easily (like rubber, glass, and plastic). Electrons cannot move easily through an insulator. Insulators help keep a charge in place. Electric wires are covered with insulation to keep the electric charge concentrated in the wires and to protect materials that the live electricity could hurt or damage. The insulation around electric wires also helps to prevent live electrical wires from touching each other and causing a short circuit.
Grade Level Appropriate Concepts
As in the teaching of any area of science it is important to carefully consider the appropriate grade level for the concepts intended to be taught. According to the National Science Education Standards (NSES), it may be premature to introduce atoms in the early grades as a means to explain the properties of elements and compounds, focusing, instead, on the macroscopic features of substances. This may be the reason that electricity is confined to the study of circuits without mention of the charges that produce the currents. In the middle grades fundamental particles can be used to explain how materials become charged. In the high school, students develop the ability to relate the macroscopic properties of substances to the microscopic structure of substances. The idea that matter is made of minute particles called atoms, which are composed of even smaller particles, is introduced along with the measurable properties of mass and charge. Use of technology and mathematics assume a greater role in investigations.
Naïve Ideas
1.After a material acquires a positive charge, it has more positive charges (protons) than it did.
2.When a material has positive charge, the missing negative charges (electrons) have been destroyed.
3.Whenever a material becomes charged, the charges have been newly created in the process.
4.Positively charged atoms give a positive charge; negatively charged atoms give a negative charge.
5.Static electric forces are always attractive.
6.In order for an object to act like it is charged, electrons must be added or removed.
7.All wires must be coated with an insulating material or the electricity will leak out.
B. Wonderment of Producing Static Charge
1. Rubbing
The Fluttering Butterfly
Objective: To produce a static charge by friction and observe the effect on butterfly wings.
Materials: colored pencils or crayons, tissue or other lightweight paper, stick glue, construction paper, balloon or comb, wool cloth
Procedure
1.We have prepared the activity by:
a.Drawing a butterfly onto a 8-cm square piece of tissue or lightweight paper
b.Cutting out the butterfly design. We put a small amount of glue on the body, being extra careful not to get any glue on the wings and glued the butterfly on the paper.
c.Allowing the glue to dry.
2.You should crease the wings next to the body so they will bend up and down easily.
3.Hold the uncharged balloon or comb NEAR the wings, then move away and observe.
4.Charge a balloon or comb by rubbing it with the wool. (Your hair works, too!)
5.Hold the charged balloon or comb NEAR the wings, then move away. Repeat several times.
Notes: The type of electricity made when you rub a rubber comb with a piece of woolen cloth is called “static” electricity. “Static” means “standing” in Greek. Static electricity is produced when two things are rubbed together. The butterfly overlay was produced using an Ellison Decorative Die, which was available at our local IntermediateSchool District.
The Static Mystery
Objective: To produce a charge on a balloon and observe that the charge does not spread equally over its entire surface.
Materials:balloons, piece of wool, small pieces of paper or Styrofoam, permanent marker
Procedure
1.Inflate a balloon, then use marker to make three lines, evenly spaced around the balloon. (See diagram). Number the lines 1, 2, and 3.
2.Try the small pieces of paper or Styrofoam to determine if there is a charge on the balloon.
3.After the marks have dried on the balloon, give the marked balloon and the wool cloth to another person. That person should, without you seeing, rub the balloon along only one of the three lines being careful to handle the balloon by the knot.
4.The person should then return the balloon to you and challenge you to use the small pieces of paper or Styrofoam to discover which line was rubbed.
Notes: objects can be charged by rubbing them together. As the two objects touch, one gives up loosely held outermost electrons to the other. Thus, this transfer of electrons produces a static charge.
2. Contact
The Fickle Friends
Objective:To demonstrate that a charged object can transfer charge to a neutral object.
Materials:hard-rubber comb, piece of woolen cloth, pepper or Styrofoam spheres or powdered cork
Procedure
1. Sprinkle some of the pepper over the uncharged comb.
2. Notice the movement of the pepper as it moves toward and reaches the comb.
3. Rub the comb with the wool.
4. Sprinkle some of the pepper over the charged comb.
5. Notice the movement of the pepper as it moves toward and reaches the comb.
6. Repeat the above steps using Styrofoam spheres.
7. Repeat the above steps using powdered cork.
Notes: The small pieces are neutral, and when they come near the negatively charged comb they are attracted to it. But they won’t remain “friends” for long. As soon as they get a negative charge too, they jump away from the comb.
A material can be charged if electrons are transferred from one material to another by contact. This generally happens when one material is charged and it touches either a neutral or oppositely charged material. Since the comb transfers some of its electrons to the pepper the comb and the pepper have the same charge and repel one another.
The Repulsive Ball
Objective: To observe the effect of charging an object by contact.
Materials:balloon, Styrofoam ball, aluminum foil, piece of wool, packing "peanut"
Procedure
1. Attach a piece of string to a ping pong ball.
2. Cut a piece of aluminum foil into a square 10-cm. on a side and cover the ping pong ball with the foil.
4. Bring a uncharged balloon near the suspended ball and observe the reaction of the ping pong ball.
3. Charge a balloon by rubbing with a piece of wool.
4. Bring a charged balloon near the suspended ball and observe the reaction of the ping pong ball.
5. Attach a string to a packing "peanut".
6. Bring the charged balloon near the "peanut" and observe the reaction.
Notes: The ping pong ball is attracted toward to the balloon and will touch the balloon. Upon touching the balloon the ping pong ball jumps away after being charged by contact.
A material can be charged if electrons are transferred from one material to another by contact. This generally happens when one material is charged and it touches either a neutral or oppositely charged material. Since the balloon transfers some of its electrons to the ping pong ball the balloon and the ping pong ball have the same charge and repel one another.
3. Induction
Dancing Spheres In Captivity
Objective: To observe that a neutral object can be attracted to a charged object by induction.
Materials:clear acrylic or cellulose packing tube. two lids, so that the tube can remain closed, tiny candy balls (the kind used to decorate cakes and cookies) wool cloth.
Procedure
1. Place about 30 or 40 candy balls inside the plastic tube. Cap both ends closed. If you have little children, you might want to glue the caps onto the ends.
2. Rub the closed tube vigorously with the cloth.
3. Observe how the balls interact with each other.
4. Move your finger along the tube and observe what happens.
Notes: Fine points to discuss
What makes the beads/balls move?
Is there a pattern to their movement?
How can you control their movement?
What happens if you rub the tube with (or on) different materials?
What happens to the tube if you leave the tube undisturbed for awhile?
What happens to the beads/balls if you rub one end of the tube?
Can you make the beads/balls move without sticking to the tube or to each other?
How can you get rid of the static charge inside the tube?
What happens when you bring two static tubes next to each other?
Do the beads/balls behave the same way inside of other plastic containers?
Do other particles behave the same way as beads/balls inside a plastic tube?
Flex Tubes (clear cellulose packing tubes) can be ordered from Brockway-Flex Products, 445 Industrial Road, Carlsadt, N.J.07072. Tel. #800-526-6273. Wendy and Kim Nichols in their book Wonder-science suggest putting tiny Styrofoam beads inside the tube. You might want to compare how the force of static effects both materials.
When the tube is rubbed with the wool a negatively charge is produced both on the tube and on the candy balls. When your finger is brought near the tube it induces a positive charge near the surface of the candy and the small candy balls move in the tube.