Welcome to Physical Science with Mrs. Brown

1. Welcome to Physical SciencewithMrs. Brown

2. Unit 8: Electricity and Magnetism You need to know about two forces: electricity and magnetism. You will learn about these forces in this unit.

3. Lesson 1: Electric Charge Electric charges,  which can be found in all materials, cause both lightning and static electricity. Let's take a look at electric charges–what they are and how you can observe their effects.

4. How Do Electric Charges Interact? Static electric charges come from specific parts of an atom. • Every atom has a nucleus containing positively charged protons. • This nucleus is surrounded by negatively charged electrons. • A positive charge is represented by a plus sign (+). • A negative charge is represented by minus a sign (–). • Electric charges always act in a certain way: • opposite charges attract each other • like charges repel each other. • Force of attraction-the force that pulls opposite electric charges together. • It is also the force that keeps negatively charged electrons around the positively charged nucleus of an atom.

5. In Short: • Electrical charges are symbolized by (+) and (-). • Electric charges always act in a certain way: opposite charges attracteach other, and like charges repel each other. • Force of Attraction-force that pulls opposite electric charges together.

6. Atomic Particles Have Electric Charges • Electronsare particles with a negative charge. • Protonshave a positive charge. Just as you add numbers in math, you can add charges. • Negative charges cancel out positive ones, so equal numbers of each charge…is neutral combination (it has no charge). • Therefore, atoms with the same number of protons and electrons are electrically neutral—they have no charge. • An atom that has unequal numbers of protons and electrons is a charged particle called an ion. • The charge of an ion is equal to the number of protons minus the number of electrons. • Ion with more protons than electrons, has a positive charge. • Ion with more electrons than protons, has a negative charge

7. In Short: • Charge of Atomic Particles: • Electrons have a negative charge. e- • Protons have a positive charge. p+ • Equal numbers of both p+ & e- equal a neutral charge. • An atom that has unequal numbers of protons and electrons is a charged particle called an ion.

8. Electric Fields • A particle that has an electric charge affects the space around it. • The electric influence around a charge is called its electric field. • The effect of a particle’s electric field on other objects depends on the objects’ distance from the charge. In other words: • The force between two charges depends on the amount of charge and the distance between them. • The amount of charge is shown by the number of plus (+) signs. • If the amount of charge increases, the force of attraction or repulsion between them increases. • If the distance between the charges increases, the force between the charges decreases. • This applies to both attraction and repulsion. An electroscope is an instrument for detecting static electricity.

9. Lesson 2: Electric Currents  Electricity powers everything from lights to trains because it can send power through wires, often over great distances. Let’s take a closer look at how electricity moves.

10. Electric Currents Static electricity is composed of charges, from an excess or shortage of electrons. • These static charges can be built up by rubbing different materials together so that the electrons move from one substance to another. Electric current occurs when there is a flow or movement of negatively charged electrons. • A quick discharge of static electricity is an example of such a current. • Ex. How lightning forms, or the shock you get from a doorknob. But appliances don’t run on quick static discharges. Usable electricity comes in a continuous current. To control and direct a continuous current, we use conductors, insulators, and resistors.

11. Conductors Carry Currents • If you take apart a wire, you will find the inside is made of one or more strands of metal, usually copper or aluminum. • In metals like these, many of the electrons are free to move throughout the metal…allowing them to carry an electric current. • Materials like these are called conductors, and they are used to carry electricity from place to place.  • Think of a conductor as a tube and electricity as water flowing inside it.

12. Insulators Stop Currents • The outside of a wire is usually covered with plastic, although you might find fabric-wrapped wires in an old house. • In some materials, atoms hold onto their electrons. • Electrons are not free to move in materials are called insulators, so it’s difficult for an electric current to flow, stopping the movement of electricity. • Ex. Glass, porcelain, rubber, and many plastics are insulators. • Note: Do Not assume all non-metal materials will act as insulators. Water, wax, and many other substances may surprise you by conducting an electric current

13. Resistance and Electrical Currents • There are no ideal conductors or insulators. • Even the best conductors can slow down an electric current. • Insulators can be overwhelmed by so much electricity that the electricity will  begin to flow. • In addition to conductors and insulators, there are substances that allow some movement of electrons. • As the electrons are slowed down, some of their energy is converted to heat (thermal energy). • We call this slowing down of electrical current electrical resistance.

14. In Short: • Conductor-any material through which electricity can flow. A copper wire is a good conductor of electric charge as it flows through the circuit. EX. Copper & aluminum. • Insulator-substance that cannot conduct electricity very well. The rubber casing around the speaker wire serves as an insulator for the electrical current. EX. Glass, porcelain, rubber and many plastics.

15. What Makes Electrical Currents Flow? • In a previous lesson, you learned that rubbing different materials together moves electrons and builds up a static charge. • Chemical reactions in a battery, light falling on a photovoltaic (PV) cell, moving magnetic and electrical fields in a generator, or even stored up static electrons repel one another and are attracted to objects with a positive charge, they will flow from negative to positive charge in a device called a capacitor can all drive electric currents.

17. Can Electrons Be Used Up? It’s possible for the flow of electrical current to lead to a dead end. • Building and releasing static charges or charging and discharging a battery can lead to filled capacity or use up available electrons. • Electric currents that provide a continuous push to keep the electrons flowing are useful. (what powers the appliances your home)

18. Lesson 3: Electric Circuits  The energy for all of these things comes from an electric current–a stream of moving electrons–that flows through the computer.

19. Electrons, which all have negative charges, repel one another. If electrons are lined up in a conductor, such as in a copper wire, what do you think will happen when an extra electron enters the line? All the electrons shift forward due to the force of repulsion. • So, what happens if the force stops pushing the electrons, or the current reaches the end of the line? The current stops flowing. This is good if you’re standing in a line, but it’s bad if you’re relying on electric current to power your computer.

20. Circuits: Keeping the Flow • An electrical current can only exist if electrons are flowing. • The current needs a medium, or conductor, through which to flow…the conductor always has some resistancebut electrons continue to flow if a constant force is pushing on them. • If the conductor ends at the same place it begins, the force of repulsion will continue to keep the electrons moving…this continuous loop of electrical conductors is a circuit.

21. Circuits: Not Just a Bunch of Wires • Even though copper wire is an excellent conductor of electricity, you can’t just twist two ends of a copper wire together and expect electrons to flow…currents form when electrons repel one another. • To create an electric circuit, you need a source of electrons that will push into the loop and cause the current to flow. • Many labs use a battery for current since it is less dangerous. • Batteriescreate an electric field with chemical reactions. • One chemical in the battery has a tendency to lose electrons, while another has a tendency to gain them. • The difference in their tendencies to hold electrons establishes the electric field, with one pole being more negative and the other pole more positive

22. Resistors: Resisting The Flow • A resistor is anything that resists the flow of electrons. • If you add a light bulb to the circuit, the filament in the bulb will resist the flow of electrons and convert energy into light and heat. • You know the circuit is functioning because the bulb will glow. • Electric current will only flow in a circuit if the circuit is closed, meaning that there are no breaks in the circuit.

23. Switches Stop The Flow • An electric charge needs a closed circuit to flow. • Switches can be used to control the flow of electrons by opening and closing the circuit. • When the circuit is open…electrons cannot flow and the bulb will not light. • Some open circuits happen by accident. • When the filament of a light bulb burns out, it creates a break in the circuit…the circuit becomes open, and the flow stops. To close the circuit, the bulb must be replaced

24. Series Circuits Did you ever see a string of holiday lights all go dark even though only one bulb has stopped working? • This happens when bulbs are wired in a series circuit--the current flows through one bulb to a conductor that leads to the next bulb, all the way down the line. • In a series circuit, the electrons can follow only one path. • With only one wire connecting all the bulbs, if there is a break in the circuit between any two bulbs, all the bulbs go dark…or if the filament of any of the bulbs burns out, the circuit is opened and again, all the bulbs go dark

25. Parallel Circuits These days, most strings of holiday lights stay lit even though one bulb may be out. • Bulbs are not dependent on each other to stay lit…this is called a parallel circuit. • The current can follow multiple paths past the resistors. • There are multiple, intertwined wires going from bulb to bulb. • Those multiple wires are alternate paths for electricity. • The current flows from the electrical source through each possible path, lighting all the lights. • If one of the wires breaks, or if the filament in a bulb burns out, all the other paths are still closed circuits. • Only the one light bulb goes dark

26. In Short: • Parts of an electrical circuit: • a source of electrons • a wire • a resistor (like a light bulb) • Switches to turn off and on the current • Series circuit-one wire connects all the bulbs • Parallel circuit-multiple wires connect the bulb to the circuits • Take Note of the Circuit Diagrams in this lesson.

27. (Electricity source) resistor

28. Series circuit vs. Parallel circuit

29. Lesson 6: Magnetism In this lesson, you will learn how magnets work and how the force exerted by magnets is related to the force exerted by an electric charge.

30. Magnets Magnets behave in predictable ways: • Magnets can exert a force of repulsion…they push other magnets away. • Magnets can also exert a force of attraction.

31. Bar Magnets • Bar magnets are simply pieces of magnetized metal. • All bar magnets have two ends that either attract or repel other magnetic materials. • These ends are called poles, and are normally referred to as the north pole and the south pole. • Every magnet has both a north pole and a south pole, these are called magnetic poles. • An electrically charged particle can occur with a single positive or negative charge. • But no matter how you might slice up a magnet, if it has a south pole, it will also have a north pole. • Magnetic poles always occur in pairs, which is why magnets are said to be dipolar.

32. Opposites Attract, Likes Repel • If you have two bar magnets, the north pole of one will attract the south pole of the other, but repel the north pole. • The same thing happens when two south poles meet—they repel one another. • In other words, unlike poles attract one another, and like poles repel one another…opposite charges attract, while like charges repel.

33. Domains What makes magnets magnetic? • Within certain metals, such as iron, nickel, and cobalt, tiny parts called domains are magnetic—they have poles that attract unlike poles of other magnets. • A material that contains magnetic domains but is not a magnet, the poles of the tiny magnetic domains are pointed in different directions. • An object only becomes a magnet when the domains align more in some particular direction than other directions.

34. How Are Magnets Made? Anything containing magnetic material can behave like a magnet…some magnets stay magnetic, while others do not. • Permanent magnets, such as bar magnets, are made in a factory with all their magnetic material aligned more in one direction than in others. Their overall magnetic force is strong, so they are unlikely to revert back to non-magnets, unless they are kept in close contact with other magnets. • Temporary magnets, such as a nail or the front of your refrigerator, contain magnetic domains. They behave like magnets only when in the presence of magnets. When you stick a magnet to your refrigerator door, the fridge behaves like a magnet temporarily. But you’d have a tough time trying to stick a nail to your fridge, or sticking two fridges together. These items alone do not exert a discernible magnetic force.

35. Magnets Exert Force • Magnets exert a force on other magnets and on magnetic materials around them. • The effect of a magnet on the space around it is known as a magnetic field. • magnets do not have to touch an object to exert a force on it • the magnetic field around a magnet is similar to the electric field around an electric charge • the force is strongest near the poles and becomes weaker further away from the poles

36. Earth Is a Magnet • If you hang a bar magnet from a string tied to its center and allow it to swing freely, its north pole will turn toward the geographic north pole of earth. • The reason for this is that earth behaves like a giant bar magnet. • Centuries ago, sailors realized that if they marked one end of a magnetized rock and allowed it to float on some wood, it would always turn toward the north. • This is how compasses were invented.

37. Magnetic Domains and Electric Charges By now, you may have begun to notice that magnetic domains have a lot in common with electric charges:   • Opposites attract, likes repel • Both act on other objects at a distance. 

38. Lesson 7: Electricity and Magnetism In this lesson, we will learn how the force exerted by magnets is related to the force exerted by an electric charge and how the forces are used to accomplish work.

39. Electromagnets • Electricity and magnetism are related. • In fact, you can actually use moving electric charges to produce a magnetic field in the space around them. • You can also use a changing magnetic field to generate an electric current. Let’s see how this is done

40. A Temporary Magnet • A temporary magnet called an electromagnet. • Thick electrical wires wrapped around a large piece of iron produce a strong magnetic field. • As long as electric charges are flowing through the wires, the electromagnet holds the metal tightly. • The electric current stops flowing through the wire, and the magnetic field disappears. • K12 Ex. Salvage Yard Crane

41. Parts of an Electromagnet Simply put, electromagnets are temporary magnets that use electricity to produce a magnetic field. • A simple electromagnet consists of 3 main parts: • electricity source: such as a battery • metallic core: such as an iron nail or screw • wire: coiled around the metal core, and connected to the battery to carry the electric current

42. Making Electromagnets • Electromagnets are simply magnets produced by passing an electric current through coils of wire. • Electromagnets work because every moving electric charge produces a magnetic field. • The more moving charges there are, the greater the magnetic field.

43. How Are Stronger Electromagnets  Made? To pick up more metal, you need to increase the strength of the electromagnet. The strength of an electromagnet depends on two factors: • the amount of electric current •the size of the wire coil

44. Strengthening Current • One way to increase the strength of an electromagnet is to increase the rate at which electrons are flowing through the wire. • Each moving charge is surrounded by a magnetic field, so increasing the rate of flow of charges increases the strength of the field. • You could also increase the current by using a different battery that produces a higher voltage

45. Adding More Coils • The second way to increase the strength of the electromagnet is to increase the number of wire coils around the nail. • As electric charges move through the wire, they form a magnetic field around the wire coil. • The electromagnet becomes stronger because of the overall increase in the number of wire coils

46. Measuring Current: Galvanometers • You can use the magnetic field around an electric current to detect and measure the current. • An instrument called a galvanometer uses a movable permanent magnet to detect the temporary magnetic field around an electric current. • The permanent magnet reacts to the presence of the magnetic field generated by an electric current. • When there is a current through the galvanometer, the magnetic field it produces causes the permanent magnet to change its direction. • A dial on the galvanometer connected to the magnet can show the strength of the current.

47. Making Electric Currents • You now know that a moving electric charge creates a magnetic field. • You may be surprised to learn that the opposite is also true. • A magnetic field can cause an electric charge to move. • The direction of flow of the electrons depends on which way the magnet moves

48. Lesson 9: Motors and Generators In this lesson, you will learn how engineers harness the power generated by the interaction between moving electric charges and magnetic fields to provide power to motors and generators.

49. Simple Electric Motors What makes the blades spin on an electric fan? • The combined effect of electric currents and magnetic forces turn electrical energy into mechanical energy. • Any time an electric current flows through a wire, the current produces a magnetic field. • Engineers use this phenomenon to build motors, such as the ones powering a fan. • These motors rely on the forces of magnetic attraction and repulsion to transform electrical energy into the mechanical energy of movement

50. Electric Motors in Action • Although their basic components are the same as the simple, battery-powered motors, larger motors provide more power, doing more work each second. • A wide variety of electric motors is used to power any number of mechanical movements. • The motions of these tools are limited only by their mechanical soundness and by their need for electrical current. • To maintain an electric supply, most electric motors are simply plugged into a wall outlet, while battery-operated motors can be run on rechargeable batteries