1. Current Electricity

2. Let’s review what we know about electric charges: Objects are made of negative and positive charges Objects are made of negative and positive charges Like charges repel and opposite charges attract Like charges repel and opposite charges attract Negative charges (electrons) are free to move from atom to atom Negative charges (electrons) are free to move from atom to atom Positive charges (protons) cannot move Positive charges (protons) cannot move

3. Current Electricity Until now, we have only been looking at charges that were static (not moving on an object). Until now, we have only been looking at charges that were static (not moving on an object). If these charges are allowed to move in a controlled way, (say in a conductor) it is now called current electricity. If these charges are allowed to move in a controlled way, (say in a conductor) it is now called current electricity. In current electricity, large groups of electrons continuously move around a path. In current electricity, large groups of electrons continuously move around a path. Each electron is forced through the path by charges elsewhere in the circuit. Each electron is forced through the path by charges elsewhere in the circuit.

4. In all cases of current electricity, energy is required to move the charges around the path (called a circuit). In all cases of current electricity, energy is required to move the charges around the path (called a circuit). A cell phone uses a battery; a calculator uses a solar cell; a lamp uses the wall plug. A cell phone uses a battery; a calculator uses a solar cell; a lamp uses the wall plug.

5. Types of Current Current electricity comes in two different types: Current electricity comes in two different types: Direct Current (DC)Direct Current (DC) Alternating Current (AC)Alternating Current (AC)

6. DC Current In DC, the electrons flow around the circuit in one direction, from the negative end to the positive end. In DC, the electrons flow around the circuit in one direction, from the negative end to the positive end. Electrons flow negative to positive because they are negatively charged. Electrons flow negative to positive because they are negatively charged. Electrons are attracted to the positive end of the battery and repelled from the negative end. Electrons are attracted to the positive end of the battery and repelled from the negative end. All batteries produce DC electricity. All batteries produce DC electricity.

7. Electrochemical Cells Often mis-called ‘batteries’ Often mis-called ‘batteries’ Converts chemical energy to electrical energy Converts chemical energy to electrical energy Made up of two electrodes (conductors made of different materials) in an electrolyte (a conduction solution) Made up of two electrodes (conductors made of different materials) in an electrolyte (a conduction solution) A chemical reaction occurs with the materials to negatively charge one electrode and positively charge the other A chemical reaction occurs with the materials to negatively charge one electrode and positively charge the other

8. So What Is a Battery? A Battery is more than one cell connected together A Battery is more than one cell connected together A battery can provide more energy than a single cell A battery can provide more energy than a single cell Connecting them in different orientations gives you different amounts of energy for different amounts of time Connecting them in different orientations gives you different amounts of energy for different amounts of time

9. Primary vs Secondary Cells There are two main types of cells: There are two main types of cells: PrimaryPrimary Chemical reactions are not reversible Chemical reactions are not reversible Once all of the chemicals are used up, they are useless Once all of the chemicals are used up, they are useless SecondarySecondary Chemical reactions are reversible Chemical reactions are reversible Once the chemicals are used up, electricity (from a charger) can be used to reverse the chemical reaction Once the chemicals are used up, electricity (from a charger) can be used to reverse the chemical reaction There is a limit to how many times they can be charged and discharged There is a limit to how many times they can be charged and discharged

10. Fuel Cell A fuel cell works much like a regular electrochemical cell A fuel cell works much like a regular electrochemical cell The main difference is that the waste chemicals are constantly removed from the reaction so that only the desired chemicals are present The main difference is that the waste chemicals are constantly removed from the reaction so that only the desired chemicals are present Fuel cells can last much longer than conventional cells Fuel cells can last much longer than conventional cells

11. AC Sources

12. AC Generators All AC generators work on the same principle All AC generators work on the same principle They convert mechanical energy (motion) into electrical energy They convert mechanical energy (motion) into electrical energy A coil of wire is spun in between two powerful magnets A coil of wire is spun in between two powerful magnets Due to ‘electromagnetic induction’, electricity is produced in the coil Due to ‘electromagnetic induction’, electricity is produced in the coil

13. Ways to spin the coil… All generators need ways to spin the coil of wire All generators need ways to spin the coil of wire Hydroelectricity uses falling waterHydroelectricity uses falling water Wind turbines use windWind turbines use wind Nuclear plants use steam to turn turbinesNuclear plants use steam to turn turbines

14. How does AC work? http://www.youtube.com/watch?v=h P1r7sRVgas&feature=fvwrel http://www.youtube.com/watch?v=h P1r7sRVgas&feature=fvwrel http://www.youtube.com/watch?v=h P1r7sRVgas&feature=fvwrel http://www.youtube.com/watch?v=h P1r7sRVgas&feature=fvwrel

15. Homework Read p432-6 Read p432-6 Answer Questions 1-5 on p 436 Answer Questions 1-5 on p 436 Read p437-8 Read p437-8 Answer Questions 1-5 on p 438 Answer Questions 1-5 on p 438