Electricity and magnetism

1. CHAPTER 7 Electricity and magnetism

2. Section 1 Electric Charge and Forces

3. Electric Charges • Atoms are made of electrons moving around a nucleus (protons and neutrons). • Protons have a positive charge. • Neutrons have a neutral or no charge. • Electrons have a negative charge. • Atoms are electrically neutral in charge having equal protons and electrons. • Losing an electron makes the atom positively charged. • Gaining an electron makes the atom negatively charged.

4. Forces Between Charges • Like charges repel and unlike charges attract • Distance and amount of charge determines the force between objects • Greater distance = less force • Greater amount = greater force

5. Electric Field and Forces • Objects do not have to touch to exert electric forces on each other • Electric fields surround every proton and electron • Electric fields are invisible and at every point in space surrounding a charge.

6. Electrically Charging Objects • Charging by contact – objects must come into direct contact with each other • Electrons are gained by one object and lost by the other • Charging by induction – rearranging electric charges due to the presence of an electric field • One part of the object is positively charged while another part is negatively charged

7. Conductors and Insulators • Conductors hold electrons so loosely that they can move through the material easily • Silver, gold, copper • Insulators hold electrons so tightly that they cannot move through the material easily • Plastic, glass, rubber, wood

8. Static Charge • The imbalance of electric charges on an object is called static charge. • Occurs during charging by contact • The movement of static charge from one place to another is called electric discharge. • Lightning – may occur between cloud and ground, within cloud, or between clouds

9. Electrostatic potential • 30,000 volts removing sweater • 10,000 volts using a comb • 3,000 volts walking on carpet • 1,000 volts putting on coat • LUCKY FOR US, these high volts have very low amperage.

10. Lightning Safety • 30-30 rule • If there is 30 seconds between thunder and lightning, seek shelter and stay away from metals. • Wait 30 minutes after last lightning strike before leaving shelter. • Storm clouds need not be present for lightning to strike. • Grounding is providing a path to drain excess electric charges into Earth • Lightning rods

11. FUN FACTS • 50-100 lightning bolts hit the ground every second on Earth. • Lightning discharge 100 million volts of electricity, heating the air to 60,000 degrees F. • Bolts can be up to 100 miles long • Steel turns into a magnet if struck be lightning.

12. Section 2 Electric Current

13. Electric Current • The flow of electric charges • Electrons in a wire moving along the wire • Equal numbers of protons and electrons in wire making it electrically neutral • Equal numbers of electrons entering wire and exiting the other end • Measured in amperes (A) = the amount of electrons flowing in and out of wire every second [about 6 billion billion]

14. Simple Electric Circuit • Electricity is either static or current • Static - electrons accumulate and "stand" on the surface • Current - electrons must "flow" through something • Direct current (DC) - flow in one direction (battery) • Alternating current (AC) - reverses its flow many times a second (household power) • Electric current will flow continually on a closed path known as an electric circuit • Broken wires, opened switch, broken filament will stop current flowing

15. Flowing Electric Charges • A force must be exerted on electric charges to make them flow • An electric field in the circuit will move electrons in a single direction • A battery will produce an electric field when a chemical reaction in the battery occurs. • Charges terminals of battery – and + • Electrons flow from – to +

16. Electrical Resistance • Electrons have trillions of collisions every second inside batteries changing their direction and speed • The electric field keeps the electrons flowing in the direction of the current • The measure of how difficult it is for an electron to flow in an object is known as electricresistance. • Measured using ohms (Ω)

17. Electrical Energy Transfer • Electrons flowing through a circuit have kinetic energy • Every collision causes some energy to be converted into heat and light • As the strength of the electric field increases so does the kinetic energy of the flowing electrons

18. Voltage • The measure of electrical energy transferred by an electron as it moves from one point to another in a circuit • Measured using a voltmeter • Battery voltage indicates that there is more electrical energy transferred in higher voltage

19. Ohm’s Law • Shows relationship between voltage, current, and resistance • As voltage increases, current in the circuit increases. • Increasing resistance slows down the current flow • voltage(V) = current(A) X resistance(Ω) V = IR

20. Series and Parallel Circuits • Devices connected so there is only one closed path for current to follow is a series circuit. • Any part of path broken, current will not flow. • Devices connected so there is more than one closed path for current to follow is called a parallel circuit. • If one path is broken, current will continue to flow through another path.

21. Electric Cost • Companies charge by the kilowatt-hour (kWh) • That is the amount of energy equal to 1kW of power continuously for 1 hour • About ten 100-W light bulbs for 1 hour

22. Section 3 Magnetism

23. Magnetic Poles • Every magnet has a north and a south pole. • Magnetic poles are like electric charges. • Like poles repel; unlike poles attract. • Forces are stronger the closer they are to each other. • Magnetic fields are like electrical fields. • Fields are stronger at the poles of magnets.

24. Magnetic Materials • Metals that contain iron, nickel, cobalt and a few other rare-earth elements • Objects that do not contain the above elements are not effected by magnetic fields.

25. Magnetic Domain • A group of atoms that have their magnetic poles pointing in the same direction has magnetic domain. • With magnetic domains aligned in a single direction, the magnetic field is stronger. • Materials become magnetized when magnets exert forces on the materials magnetic domains.

26. Electromagnetism • Discovered in early 1800s, a wire carrying an electric current is surrounded by a magnetic field • Magnetic fields can be made stronger by wrapping the wire around an iron core. • Increasing current, increases the magnetic field. • Electromagnets are temporary and can be controlled.

27. Generating Electric Current • Moving a magnet through a wire loop that is part of a circuit makes an electric current flow – electromagnetic induction • Generators convert mechanical energy to electrical energy. • Power plants use steam or moving water to convert mechanical energy to electrical energy.