1. Chapter 20 Electric Current Electricity and Energy Song Video

2. Solids: Conductors, Insulators and Semiconductors Conductors: mostly metals Conductors: mostly metals Insulators: mostly nonmetal materials Insulators: mostly nonmetal materials Semiconductors: metalloids Semiconductors: metalloids

3. 3 Bonding in Metals The electron-sea model is a simple depiction of a metal as an array of positive ions surrounded by delocalized valence electrons. The electron-sea model is a simple depiction of a metal as an array of positive ions surrounded by delocalized valence electrons. –Metals are good conductors of electricity because of the mobility of these delocalized valence electrons. –A metal also conducts heat well because the mobile electrons can carry additional kinetic energy.

4. 4 Bonding in Metals

5. Semiconductors Metalloids: semiconducting elements Metalloids: semiconducting elements Low electrical conductivity at room temperature Low electrical conductivity at room temperature Electrical conductivity increases with temp. Electrical conductivity increases with temp.

6. Semiconductors Semiconducting elements form the basis of solid state electronic devices. Semiconducting elements form the basis of solid state electronic devices. Metalloids (such as silicon or germanium) are semiconducting elements whose electrical conductivity increases as temperature increases. Metalloids (such as silicon or germanium) are semiconducting elements whose electrical conductivity increases as temperature increases.

7. Shocking! If you reach for a metal doorknob after walking across a carpet, you might see a spark. If you reach for a metal doorknob after walking across a carpet, you might see a spark. The spark is caused by electrons moving from your hand to the doorknob. The spark is caused by electrons moving from your hand to the doorknob.

8. Conductor! A material in which electrons are able to move easily is a conductor. A material in which electrons are able to move easily is a conductor. The best electrical conductors are metals. The best electrical conductors are metals.

9. Not a Conductor! A material in which electrons are not able to move easily is an insulator. A material in which electrons are not able to move easily is an insulator. Most plastics are insulators Most plastics are insulators

10. Charging Objects Rubbing two materials together can result in a transfer of electrons. Rubbing two materials together can result in a transfer of electrons. Then one material is left with a positive charge and the other with an equal amount of negative charge. Then one material is left with a positive charge and the other with an equal amount of negative charge. The process of transferring charge by touching or rubbing is called charging by contact. The process of transferring charge by touching or rubbing is called charging by contact.

11. INDUCTION! Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction. The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction.

12. Induction The balloon on the left is neutral. The balloon on the right is negatively charged. It produces a positively charged area on the sleeve by repelling electrons.

13. Current and Potential The net movement of electric charges in a single direction is an electric current. The net movement of electric charges in a single direction is an electric current. In a metal wire, or any material, electrons are in constant motion in all directions. As a result, there is no net movement of electrons in one direction. In a metal wire, or any material, electrons are in constant motion in all directions. As a result, there is no net movement of electrons in one direction.

14. Current and Voltage When an electric current flows in the wire, electrons continue their random movement, but they also drift in the direction that the current flows. When an electric current flows in the wire, electrons continue their random movement, but they also drift in the direction that the current flows. Electric current is measured in amperes. Electric current is measured in amperes.

15. Voltage difference In a similar way, electric charge flows from higher voltage to lower voltage. In a similar way, electric charge flows from higher voltage to lower voltage. A voltage difference is related to the force that causes electric charges to flow. Voltage difference is measured in volts. A voltage difference is related to the force that causes electric charges to flow. Voltage difference is measured in volts.

16. Electric Circuits This figure shows an electric current doing work by lighting a lightbulb. This figure shows an electric current doing work by lighting a lightbulb. A closed path that electric current follows is a circuit. A closed path that electric current follows is a circuit. If the circuit is broken by removing the battery, or the lightbulb, or one of the wires, current will not flow. If the circuit is broken by removing the battery, or the lightbulb, or one of the wires, current will not flow.

17. Resistance As the electrons flow through the filament in a lightbulb, they bump into the metal atoms that make up the filament. As the electrons flow through the filament in a lightbulb, they bump into the metal atoms that make up the filament. In these collisions, some of the electrical energy of the electrons is converted into thermal energy. In these collisions, some of the electrical energy of the electrons is converted into thermal energy. Eventually, the metal filament becomes hot enough to glow, producing radiant energy that can light up a dark room. Eventually, the metal filament becomes hot enough to glow, producing radiant energy that can light up a dark room.

18. Electric Current Electrons in motion. Electrons in motion. Current: The number of electrons that pass a specific point in a circuit in one second Current: The number of electrons that pass a specific point in a circuit in one second I = Q/t I = Q/t Circuit: electric current flows through a closed, continuous path. Circuit: electric current flows through a closed, continuous path.

19. HIGH LOW Electric Current The reason electric charge flows from one place to another is voltage. a. Voltage is the difference in electrical potential between two places where e¯ are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V).

20. Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells

21. Generating Electric Current Electrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell. Electrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell. Thermocouples: a tool that uses differences in temperature to generate electric currents. Thermocouples: a tool that uses differences in temperature to generate electric currents. Generator- next chapter but make alternating current Generator- next chapter but make alternating current

22. Types of current Direct current: electrons that flow in the same direction in a wire. (DC) Direct current: electrons that flow in the same direction in a wire. (DC) From batteries From batteries Alternating current: electrons that flow in different directions in a wire. (AC) Alternating current: electrons that flow in different directions in a wire. (AC) From Generators From Generators Used in your home Used in your home Transformers change AC to DC Transformers change AC to DC

23. Measuring Electricity Current: Measured in Amperes or amps (A) Current: Measured in Amperes or amps (A) Voltage: Measured in volts (V) Voltage: Measured in volts (V) Higher voltage, the more work the electrons can do. Higher voltage, the more work the electrons can do.

24. Measuring Electricity Resistance: the force opposing the flow of electrons. Resistance: the force opposing the flow of electrons. Measured in ohms Measured in ohms Symbol is Greek letter omega  Symbol is Greek letter omega  Thicker wire- less resistance Thicker wire- less resistance Longer wire- more resistance Longer wire- more resistance Conductors- low resistance Conductors- low resistance Insulators- high resistance Insulators- high resistance

25. Ohm’s Law The relationship among current, voltage, and resistance. The relationship among current, voltage, and resistance. Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance I = V R I = V R V I R

26. Do the Math A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? V I R

27. Do the Math A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? R =V / I R =V / I R = 12 V / 10 amp R = 12 V / 10 amp R =1.2  R =1.2  V I R

28. Do the Math Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? V I R

29. Do the Math Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? I = V / R I = V / R I = 120 V / 20 ohm I = 120 V / 20 ohm I = 6 amperes (A) I = 6 amperes (A) V I R

30. Electric power and energy Power: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance. Power: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance. P = V x I P = V x I (P) power = (V) voltage x (I) current in the circuit. (P) power = (V) voltage x (I) current in the circuit.

31. Energy Formula for energy Formula for energy E = P x t E = P x t (E) energy used = (P) power x (t) time (E) energy used = (P) power x (t) time The SI unit for energy is a joule. The SI unit for energy is a joule. Kilowatt-hour meters measure the electricity used in your home. Kilowatt-hour meters measure the electricity used in your home. (kWh) (kWh) Electricity and Energy Song Video

32. Write a Paragraph: (Ch 20) Investigate and explain the relationships among: Investigate and explain the relationships among:  current  Voltage  Resistance  power

33. Grade the paragraph Current – Current –  number of electrons that pass a specific point in a circuit in one second.  Reason it flows is due to voltage. Voltage – Voltage –  is the push that makes the electric charge move Resistance – Resistance –  force opposing the flow of electrons (or current) Power – Power –  rate electricity does work. The amount of work is determined by its resistance.