Electricity and Magnetism SPS10. Students will investigate the properties of electricity and magnetism. Investigate static electricity in terms of: friction, conduction, and induction. Explain the flow of electrons in terms of: Alternating and direct current. The relationship among voltage, resistance, and current. Simple series and parallel circuits. Investigate applications of magnetism and/or its relationship to the movement of electrical charges as it relates to: Electromagnets, simple motors, and permanent magnets.

Electricity Protons and Electrons

Electricity Everything in the world is made up of atoms. Each atom has smaller parts in it. One of those parts is called electrons. Electrons can move from atom to atom. When an electron moves to a different atom, it causes another electron to have to move. When electrons move quickly from one atom to another it is called Electricity!

Electricity (continued) When you talk to your friends on the telephone, the microphone inside of the phone’s handset changes your sound waves into electric signals. The light shines throughout your homes when you flip a switch. And if you stump your toe, your nerves send signals between your brain and muscles. All of these everyday occurrences are powered by electrical pulses. A charge is a measure of the extra positive or negative particles that an object has.

Rules of Electric Charge Opposite charges attract. Like charges repel.

Static Electricity

Static Electricity Static electricity is the study of the behavior of electric charges, including how charge is transferred between objects. The only reason that we are able to use electricity in our modern world is that it is possible to separate positive and negative charges from each other. Electric charge can be transferred by friction, conduction, and induction.

Friction Conduction Induction Transferring Charge Friction Conduction Induction Transfer of charge by rubbing two different materials together. Transfer of charge when two objects come into direct contact with each other (touching). Transfer of charge without direct contact. Rubbing a balloon in your hair. Walking across a carpet with socks on. Touching a metal sphere that has been charged by a Van de Graff generator. Being struck by lightning b/c you are standing near a tree.

Charging by Friction Example 1 Example 2

Charging by Conduction

Charging by Induction

Alternating Current Direct Current Electric Current Alternating Current Direct Current

The continuous flow of electric charge is an electric current The continuous flow of electric charge is an electric current. There are 2 types of electric current: direct current and alternating current. Direct current Flow of charges that regularly reverses direction Flow of charges in only one direction

Current Voltage Resistance Ohm’s Law Current Voltage Resistance

Ohm’s Law Most of the electrical appliances that you use in your homes each day are designed for 120 Volts (V). Light bulbs however are sold in several varieties, from dim 40 Watt light bulbs to bright 100 Watt light bulbs. These bulbs shine differently because they have different amounts of current in them. The difference in their current is because of their resistance. In other words, 40 W light bulbs have a greater resistance (less current than the 100 W bulbs) and therefore give off less light.

Ohm’s Law (continued) You have probably noticed that electrical devices such as video games or radios become warm after they have been on for a long amount of time. As the electrons collide, with the atoms of the material, some of their kinetic energy transfers. This transfer of energy causes the atoms to vibrate, and then the material warms up. As the electrons are slowed by a resistor, energy is lost in the form of heat. This means that current, resistance and voltage must be linked.

Calculating Resistance Ohm’s Law (continued) Did you know that resistance depends on the material used as well as the material’s length and temperature? Longer pieces of material have greater resistance (less current) than shorter pieces. Calculating Resistance The SI unit of resistance is the ohm, Ω, which is equal to volts per ampere. Resistance, R is measured in ohm’s Ω. Current, I is measured in amperes, A. Voltage, V is measured in volts, V.

Calculating Resistance (continued)   The SI unit of resistance is the ohm, Ω, which is equal to volts per ampere. Voltage = Resistance x Current Voltage (V) is measured in volts, V. Resistance ® is measured in ohm’s Ω. Current (I) is measured in amperes, A.

Practice Ohm’s Law Wire A has a resistance of 2 ohms. Wire B has a resistance of 2.5 ohms. Both wires have the same current. Which wire has a greater voltage? What is the current in an electric field in which voltage is 12 volts and resistance is 1.5 ohms?

Series Circuits Parallel Circuits Electric Circuits Series Circuits Parallel Circuits

Electrical Circuits If you’ve ever seen a house being built, you know that wires hidden inside the walls connect to every electrical outlet and to every light switch. The steady flow of electricity is called an electric current. A current will move along a wire or a path called a circuit. Circuit means to “go around.” There are 2 types of circuits: series circuits and parallel circuits.

Series Circuit vs. Parallel Circuit A series circuit is a circuit that has only one path for the current. A parallel circuit has two or more paths for current to travel. Series Circuit Old Christmas lights were once wired in series. If one bulb went out, they all went out. Parallel Circuit Lights in our homes are wired in parallel circuit. That is why we are able to have lights on in one room, but off in another.

Series Circuit vs. Parallel Circuits Has two or more paths for electrons to flow through Current is shared between the branches Series Parallel  Has a single loop for electrons to travel around Components are connected one after another Current has to travel through all components

Circuit Symbols

Guards/Safety Devices Against Overheating An electric fuse contains a small piece of metal that melts if the current becomes too high, opening the circuit and stopping the flow of current. A circuit breaker contains a small piece of metal that bends when it gets hot, opening the circuit and stopping the flow of current.

Magnetism

The History of Magnets Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons. Magnets have been known for centuries. The Chinese and Greeks knew about the “magical” properties of magnets. The ancient Greeks used a stone substance called “magnetite.” They discovered that the stone always pointed in the same direction. Later, stones of magnetite called “lodestones” were used in navigation.

Opposite poles: Attract Magnetic Poles Like Poles: Repel The ends of a magnet are where the magnetic effect is the strongest. These are called “poles.” Each magnet has 2 poles: 1 North & 1 South. If you cut a magnet in half, you get two magnets. Opposite poles: Attract

Permanent Magnets vs. Temporary Magnets Some magnets occur in nature. These magnets are called natural magnets. Natural magnets maintain their magnetic properties and therefore are permanent magnets. (ex. lodestone).   Some materials that are not natural magnets are easy to magnetize (ex. Iron). A material that is easily magnetized tends to lose its magnetism quickly, and is called a temporary magnet.

Electromagnetic An electric current passing through a wire causes a magnetic field. An electromagnet is a temporary magnet made by wrapping a current-carrying wire around an iron core. The center of an electromagnet is called the core, and it is often made of iron. As long as current is flowing, an electromagnet has a magnetic field. When current is turned off, there is no longer a magnetic field.

Electromagnets There are two ways to make an electromagnet stronger: increasing the number of coils increasing the amount of current Electromagnets are useful because they can be turned on and off. Electromagnets have many important uses: ex. radios, telephones, computers

Electric Motors vs. Generators An electric motor is a device that changes electrical energy into mechanical energy. An electric motor is made up of an electromagnet and a permanent magnet. So, what do windshield wipers, CD players, VCR's, blenders, ice makers, computers, and talking toys all have in common? They all contain electric motors!

Electric Motors vs. Generators A generator is a device that changes mechanical energy into electrical energy. Most of the energy we use every day comes from generators. Mechanical energy for many generators is supplied by turbines. A turbine is a large wheel that is turned by moving steam or water.

Electric Motors vs. Generators Motor or Generator? Motor or Generator?