Chapter 17 & 18 Discovery Notes

Chapter 17 – Questions 1-3 Describe how charged objects interact by using the law of electric charges. Positives are attracted to negatives. Describe 3 ways in which an object can become charged. Friction: rubbing electrons from one surface to another; Conduction: electrons move by direct contact; Induction: Electrons move and become charged WITHOUT touching! Compare conductors with insulators. Conductor allow electrons to move FREELY; Insulators prevent electrons from moving.

Chapter 17 - Questions 4-6 4. Give 2 examples of static electricity and electric discharge. Static Electricity: built up charges in clothing in a dryer and dragging your feet on the carpet. Electric discharge: Lightning and shocking yourself on a doorknob 5. What are the 2 types of charged particles in atoms? Protons and Electrons 6. What can you do with an electroscope? See if an object is charged.

Chapter 17 – Questions 7-9 7. What is electric discharge? The release of electricity moving from one object to another. 8. Why is it dangerous to be outside in an open area during a storm? Lightning usually strikes the highest object in an area. 9. Describe electric current. How quickly a charge passes through a wire; measured in AMPS!

Chapter 17 - Questions 10-12 10. Describe voltage and its relationship to electric current. The size of an electric current depends on how much voltage is applied. More voltage = more current! 11. Describe resistance and its relationship to electric current. More resistance = less current and vice versa! 12. Explain how a cell generates electrical energy. Converts chemical energy to electrical energy (like a battery).

Chapter 17 - Questions 13-15 13. Describe how thermocouples and photocells generate electrical energy. Thermocells change heat (thermal energy) into electrical energy; Photocell convert light energy into electrical energy. 14. What is the unit of measurement for electric current? Amperes (AMPS) 15. What are 2 kinds of electric current? AC (Alternating Current) and DC (Direct Current)

Chapter 17 - Questions 16-18 16. What is the unit of measurement for voltage? volts 17. What are the 2 kinds of cells? wet and dry 18. What device converts light energy into electrical energy? photocell

Chapter 17 - Questions 19-21 19. What is the formula for calculating Ohm’s Law? What do each of the letters represent? R (Resistance) = V (Voltage)/I (Current) or V(Voltage) = I (Current) X R(Resistance); unit is the ohm (Ω) 20. What is the formula for calculating electric power? What do each of the letters represent? P (Power) = V (Voltage) X I (Current); unit is watt or kilowatt 21. What are 2 common units for electric power? Watt or Kilowatt

Chapter 17 - Questions 22-24 22. What is the formula for calculating electrical energy? What do each of the letters represent? E (Electrical Energy) = P(Power) X t (Time) 23. What unit of measurement is usually used to express electrical energy? Kilowatt-hours (kWh) 24. A computer monitor draws 1.2 A at a voltage of 120 V. What is the power rating of the monitor? 144W

Chapter 17 - Questions 25-27 25. A light bulb draws a 0.5 A current at a voltage of 120 V. What is the power rating of the light bulb? 60W 26. How much electrical energy does a 100 W light bulb use if it is left on for 24 hours? 2.4 kWh 27. Name the 3 essential parts of a circuit. Energy source, wires, and a load

Chapter 17 - Questions 28-30 Parallel Circuit 28. Illustrate a series circuit and a parallel circuit. Series Circuit 29. Compare series circuits with parallel circuits. In a Series circuit all parts are connected in ONE SINGLE LOOP. In a Parallel Circuit parts are connected SIDE BY SIDE, so if part of the circuit stops working the charges still flow. Explain how fused and circuit breakers protect your home against short circuits and circuit overloads. A fuse has a thin strip of metal that expands and contracts in the presence of current. If the current is too high, the metal strip melts and the circuit is broken – preventing electrical fires. Circuit Breakers are switches that automatically open with the current is too high. If there is not a connection, current cannot flow. Therefore it prevents electrical fires as well. 30. How are loads connected in a series circuit? In a single loop or straight line. Parallel Circuit

Chapter 17 - Questions 31-32 31. How are loads connected in a parallel circuit? Side by side 32. What are 2 safety devices used in circuits? Fuses and Circuit Breakers

Chapter 18 - Questions 1-3 Describe the properties of magnets. 2 poles, exert magnetic force, surrounded by magnetic field Explain why some materials are magnetic and some are not. The arrangement of the atoms (called domains) determine whether an object is magnetic or not. Describe 4 kinds of magnets. Ferromagnets – made of iron, nickel, cobalt, etc. Electromagnets – magnet made by an electric current Temporary Magnets – made from materials that are easy to magnetize – lose magnetism easily Permanent Magnets – difficult to magnetize, but keep magnetism indefinitely

Chapter 18 - Questions 4-6 4. Give 2 examples of the effect of Earth’s magnetic field. Poles like a compass needle, Spinning electrons cause movement ; magnetic field 5. If 2 magnets push each other away, what can you conclude about their poles? They carry the same charge. 6. Why are copper and aluminum not magnetic? Their atomic structure does not allow for it.

Chapter 18 - Questions 7-9 7. Describe 2 ways a magnet can lose its magnetic properties. Striking it or heating it 8. What are ferromagnets? Magnets made with iron, nickel, or cobalt 9. What do scientists think causes Earth’s magnetic field? The movement of electric charges at Earth’s solid inner core (made of iron and nickel).

Chapter 18 - Questions 10-12 10. Identify the relationship between an electric current and a magnetic field. A current carrying wire causes a magnet to move. 11. Compare solenoids and electromagnets. Solenoids: a coil of wire with an electric current running through it. Electromagnet: a magnet that has an electric current attached that can be switched on and off. A solenoid is part of an electromagnet. 12. Describe how electromagnetism is involved in the operation of doorbells, electric motors, and galvanometers. An electric current moves in a solenoid that is attached to a magnetic material . This allows the electric current to move so your doorbell rings, motor runs, and galvanometer to measure the movement.

Chapter 18 - Questions 13-15 13. What is electromagnetism? The interaction between electricity and magnetism. 14. What happens to the magnetic field of an electromagnet if you increase the current in the wire? The field gets bigger or stronger. 15. Why does a current carrying wire cause a compass needle to move? The electric current creates a magnet field that exerts a force on the compass needle and causes it to move.

Chapter 18 – questions 16-18 16. What does a galvanometer measure? Current 17. Explain how a magnetic field can make an electric current. The movement in a magnetic field induces (makes it move without touching it) an electric current. 18. Explain how electromagnetic induction is used in a generator. Electromagnetic induction is used to change mechanical energy to electrical energy.

Chapter 18 – questions 19-21 19. Compare step-up and step-down transformers. Step- up increase voltage; Step-down decreases voltage. 20. What was Faraday trying to do in his experiment? Prove that an electromagnet could induce an electric current. 21. What energy change happens in an electric generator? Changes mechanical energy to mechanical energy.

Chapter 18 – questions 22-23 22. What are 3 sources of energy that are used to generate electrical energy? Nuclear reaction, fossil fuels, and wind. 23. What does a transformer do? Increases or decreases the voltage of an alternating current. 24. What is AC and DC? AC = Alternating Current – current travelling in both directions. DC = Direct Current – current travelling in one direction.