1. From yesterday… What are the 4 basic elements that a circuit includes? ▫Source, conductor, load, control Draw a simple circuit which includes 1 light bulb, a battery and a switch. What is potential difference? ▫Difference in energy per unit of charge between one point in the current and another- referred to as voltage

2. Topic 2 Review: 1.Matching answers: Load- water wheel Switch-valve Electric current-flow rate Voltage-pressure Battery-pump Conductor (wire)-pipe 2. Drawing a circuit with a battery, a switch, a lamp, an ammeter, and conducting wires. 4. The current passing through the electric iron would be greater because an iron requires far more energy (E in joules) than the much smaller razor. Since V = E/Q (Q = E/V) the iron would require more coulombs of charge than the razor. If I = Q/t and Q is larger than I, the current would be greater

3. Resisting the Movement of Charge Topic 3 Pages 279- 291

4. Different Types of Circuits Series Circuit: ▫Only 1 current path! ▫All moving charges travel through each component in a circuit Parallel Circuit: ▫Several current paths ▫The total current is divided with charges travelling through each branch, or part of the circuit.

5. House Wiring Most circuits around the house are parallel ▫The voltage across each load in a parallel circuit is the same ▫Problem:  Current through wires connected to the source increases whenever another branch in the circuit is closed.  Increases temperature and can cause fires!

6. What is resistance? Is a property of a substance that hinders motion of electric charge and converts electric energy into other forms of energy. ▫Example: light bulb with tungsten filament vs. light bulb with copper filament. ▫Electrons (-) force their way through solids, overcoming resistance caused by the attraction of positively charged atomic nuclei.

7. Remember: ▫Current is movement of electrons through conductors ▫Voltage is what makes electrons move ▫Resistance is what opposes the motion of the electrons. ▫A good conductor has LOW resistance ▫A poor conductor has HIGH resistance

8. The unit for resistance is ohm (Ω) ▫Measured using an ohmmeter or ▫Multimeter

9. Measuring Resistance Resistance affects current flow and potential difference in a circuit Resistance= voltage (potential difference) current This is called Ohm’s Law: R= V I

10. Let’s try some problems! Together: What is the resistance of an electric heater, if a current of 12.5A runs through it when it is connected to a 120V wall outlet?

11. To Do: 1.What is the resistance of a light bulb if a 12V battery sends a current of 2.4A through it? 2.A toaster with a resistance of 145Ω is connected to a 120V source. What current will flow through the toaster? 3.What is the potential difference across a 1500Ω resistor carrying a current of 0.075A (74mA)?

12. Read page 283: Resistors: ▫What are resistors? ▫What is one problem that is encountered with resistors? ▫What is a major use of them? ▫What materials are resistors commonly made of? Variable Resistors: ▫What changes with variable resistors? ▫Where are variable resistors used? Give examples

13. Resistors: control current or voltage to suit the specific needs of the loads in a circuit. Problems? Can be single-use, expensive, or hard to replace. Common use: circuit boards Made of: metal oxides, metal film, resistance wire Variable resistors don’t have a fixed resistance ▫Changes with temperature, light, voltage, etc. Types: rheostats, thermistors, varistors ▫Examples: Thermostat, dimmer-switch, surge protector

14. To Do: Read page 291 about the cross-section of a wire. Resistance Calculations Worksheet Topic 3 Review ▫Pg. 291, #1-5