Science: An Elementary Teacher’s Guide/Electricity and magnetism
Overview[edit | edit source]
Electricity lights up our homes, cooks our food, powers our computers, television sets, and other electronic devices. We interact with electricity every day, but may not understand what is happening when we turn on the TV or answer our phone. This chapter explains various concepts related to the electromagnetic force, including static electricity, current electricity, electrical circuits, and creating electricity with use of magnets.
All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles making up an atom are the proton, the neutron and the electron. Electrons are in a constant state of motion, spinning around the center (nucleus) of each atom. The nucleus is made up of neutrons and protons. Electrons contain a negative charge, protons a positive charge (neutrons are neutral – they have neither a positive nor a negative charge). Electricity that we use in our appliances is a controlled flow of electrons, or an electric current. Within a copper wire, for example, electrons can be forced from one atom to the next by applying a charge (a voltage) to the wire. As those electrons pass through a light bulb, for example, the potential energy of the voltage can be converted to another form of energy, such as light or heat. Here is an external link with a good lesson about electricity. Also, if you wonder the differences between volts, watts, and amps, here is a good explanation.
Static Electricity[edit | edit source]
Static electricity is the build up of an electrical charge on the surface of an object. It's called "static" because the charges remain in one area for a while rather than moving or "flowing" to another area. We see static electricity every day, and it can even build up on us. For example, when we rub our feet on the carpet we collect a static charge. When we then zap something (or someone) we release the static charge (it becomes a current for a brief moment). We also see it when our hair gets charged and sticks straight up or when our pant legs keep sticking to our legs no matter what we try and do. Another way to think of static electricity is a charge difference between two objects that are separated by an insulator (such as air). When enough of a charge has built up, or the objects are close enough together, then the static can discharge quickly, creating a spark. A car's spark plug can produce a spark thousands of times per second, as seen in this video.
So what exactly is static?
In our study of atoms we learned that atoms are made up of neutrons, protons, and electrons. The electrons are spinning around the outside. A static charge is formed when two surfaces touch each other and the electrons move from one object to another. One object will have a positive charge and the other a negative charge. Rubbing the items quickly, like when you rub a balloon fast over something or your feet on the carpet, will build up a large charge. Items with different charges (positive and negative) will attract, while items with similar charges (positive and positive) will push away from each other. Sort of like a magnet.
As clouds move, the small particles of ice bump into each other, creating static. Entire regions of the cloud begin to build up charges (usually negative at the bottom and positive at the top). When the attraction between negative and positive areas is strong enough it overcomes the insulation of the air and discharges in an explosive lightning bolt! Most lightning is cloud-to-cloud or within-cloud, but the cloud bottom's large negative charge repels electrons from the surface of the earth, creating an overall positive charge beneath the cloud--hence lightning can travel from the cloud to the ground, taking the crooked path of least resistance. Cloud-to-ground lightning is only about 20% of the total lightning that we see, but it is what we worry about because it is dangerous (lightning is about 6 times hotter than the surface of the sun and carries 5,000 to 50,000 amps of electricity, at thousands of volts). At any moment it is estimated that there are 2,000 lightning storms around the world, and approximately 100 bolts of lightning per second hitting someplace on the earth. A large thunderstorm carries enough electric potential that it is equivalent to all the electricity used in the United States during a 20-minute period! Thunder is a supersonic shock wave caused by super-heating the air directly around a bolt of lightning. Since sound travels much slower than light we hear the thunder after we see the lightning (unless we are very close). It takes sound about 5 seconds to travel 1 mile, so counting the number of seconds between the flash of lightning and the clap of thunder, then dividing by 5, will give you the approximate distance from the lightning.
Videos on Static Electricity Experiments for students:
The Law of Electrostatic Attraction and Repulsion[edit | edit source]
Coulomb's law states that: The magnitude of the electrostatic force of interaction between two point charges is directly proportional to the scalar multiplication of the magnitudes of charges and inversely proportional to the square of the distance between them.
What are Attraction and Repulsion?
- Unlike charges attract each other (+) (-)
- Like Charges repel each other (+) (+) or (-) (-)
This means that two positively charged things will repel each other and two negatively charged things will repel each other.One positively charged thing and one negatively charged thing will attract each other.The further apart the charged things are, the weaker the forces of attraction and repulsion are.
You can show whether something is charged or not by using a gold leaf electroscope.
Current Electricity[edit | edit source]
Current electricity is a flow of electric charge. For all of our electronic gadgets we rely on a constant flow of electrons through a pathway, or circuit. In electric circuits this charge is almost always carried by moving electrons in a copper wire. It can also be carried by ions in an electrolyte (such as in a battery), or by both ions and electrons (such as in a plasma). If there is a gap or insulator in a circuit, we say that it is an "open" circuit, and the electrons cannot flow. Once the circuit is closed (for example, but flipping a switch), the electrons will once again flow. Examples of current electricity include charging the phone or using it, turning on a light, cooking on an electric stove, starting a car, playing a video game and so on.
Making Electricity[edit | edit source]
Electricity is the set of physical phenomena associated with the presence and flow of electric charge. Electricity gives a wide variety of well-known effects, such as lightning, static electricity, electromagnetic induction and electric current. In addition, electricity permits the creation and reception of electromagnetic radiation such as radio waves. In electricity, charges produce electromagnetic fields which act on other charges. Electricity occurs due to several types of physics:
electric charge: a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields, electric charges can be positive or negative.
electric field (see electrostatics): charges are surrounded by an electric field. The electric field produces a force on other charges. Changes in the electric field travel at the speed of light.
electric potential: the capacity of an electric field to do work on an electric charge, typically measured in volts.
electric current: a movement or flow of electrically charged particles, typically measured in amperes.
electromagnets: moving charges produce a magnetic field. Electric currents generate magnetic fields, and changing magnetic fields generate electric currents. Here is a tutorial on how electricity is generated on a commercial scale.
Using Electricity[edit | edit source]
Electrons can be made to move from one atom to another. When electrons move among the atoms of matter, a current of electricity is created. This is what happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to other.Electricity is conducted through some things better than others do. Its resistance measures how well something conducts electricity. Some things hold their electrons very tightly. Electrons do not move through them very well. These things are called insulators. Rubber, plastic, cloth, glass and dry air are good insulators and have very high resistance.
Closed and Open Circuits[edit | edit source]
Electricity must have a complete path from the power source. If this path is broken, the circuit is incomplete. An incomplete circuit is called an open circuit. Electricity can not flow unless the circuit is complete. A complete circuit is called a closed circuit.
Series and Parallel Circuits[edit | edit source]
Series wiring, the lights are connected in a way that current must pass through one bulb before it can get to the next. Parallel wiring, each bulb receives the current independent of the other bulbs. http://www1.curriculum.edu.au/sciencepd/electricity/images/elec_ill76.gif
Here is a link on series and parallel circuits: https://learn.sparkfun.com/tutorials/series-and-parallel-circuits
Magnetism[edit | edit source]
There are four well known strongly magnetic materials
Objects that are attracted to a magnet commonly contain one or more of these four materials.
Magnets[edit | edit source]
Magnets are either natural or manufactured. Natural magnets are commonly called lodestone. Manufactured magnets are made of special combinations of materials but must include one of the magnetic materials. Aluminum is often included because it is lightweight but still very effective. You can weaken a magnet by striking it with a hard object such as a hammer or by dropping it on a hard surface such as a concrete. Extreme heat, such as a torch, can effectively demagnetize a permanent magnet.
The Law of Magnetic Attraction and Repulsion[edit | edit source]
When the north-seeking pole of one magnet is brought near the south-seeking pole of another magnet, they attract each other. If they are brought together, they repel each other.
Conductors and Insulators
Materials that allow electrons to flow through them are called conductors. Other kind of materials that resist the flow of electrons are called insulators. Both are needed in using current electricity. Some good conductors are copper, silver, aluminum, iron, and most metals. Some good insulators are glass, rubber, wood, and dry air.
Magnetic Fields[edit | edit source]
Magnets are the strongest at the poles. Magnetic lines of force go out in all directions from the poles, and the space they occupy is called the magnetic field. For example, when laying a card or sheet of glass over a magnet and sprinkling iron filings on the card.
Examples of positive magnetic fields that one may experience on a day-to-day basis include: - Televisions Computers, cell phones, alarm clocks, motors, office equipment, electrical wiring, microwave ovens, electric blankets, power lines, radio and cell phone towers, fluorescent lights, smart meters, Wi- Fi
Finding Directions with a Magnet[edit | edit source]
- The earth as a magnet
Consists of a small magnetic material suspended in a place allowed to freely rotate.
Can be used to detect the north and south seeks poles of any magnet including the Earth.
Caring for Magnets[edit | edit source]
- Avoid striking or dropping them
- Keep away from extreme heat
- Store them properly
- To help them store their strength
Conductors and Insulators[edit | edit source]
The behavior of an object that has been charged is dependent upon whether the object is made of a conductive or a nonconductive material. Conductors are materials that permit electrons to flow freely from particle to particle. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. The distribution of charge is the result of electron movement. Since conductors allow for electrons to be transported from particle to particle, a charged object will always distribute its charge until the overall repulsive forces between excess electrons is minimized. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. The transfer of charge between objects occurs more readily if the second object is made of a conducting material. Conductors allow for charge transfer through the free movement of electrons.
In contrast to conductors, insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons; subsequently charge is seldom distributed evenly across the surface of an insulator.
While insulators are not useful for transferring charge, they do serve a critical role in electrostatic experiments and demonstrations.
Closed Circuits and Open Circuits[edit | edit source]
In order for electricity to flow, there must be a continuous, conducting path between the negative "pole" and the positive pole of the power source (battery, electricity outlet, etc.). A broken wire or an "open" (off) switch both leave gaps in a circuit preventing electrons from traveling from one side of the power source to the other. Thus, electrons will not flow. This situation is called an open circuit.
A closed (on) switch means that the circuit through the switch is connected. Thus, you have a closed circuit (a circuit with no gaps in it). Current flows from the positive side of the power source (for example, the battery) to the loads (lightbulbs, fans, and etc.) wired into the circuit and back to the negative side of the power source.
Quiz[edit | edit source]
Try this quick quiz and test what you have learned by reading this chapter!
A proton is a subatomic particle with a positive electric charge that lies within the atomic nucleus of atoms. The number of protons in the atomic nucleus is that which determines the atomic number of an element.
An electron is a negatively charged subatomic particle. It can be either free not attached to any atom or bound to the nucleus of an atom.