1. INTRODUCTION TO ELECTRIC CIRCUITS All you need to be an inventor is a good imagination and a pile of junk. -Thomas Edison What we’ll cover today: 3 characteristics of a circuit How we draw a circuit & some symbols used. Ohm’s Law- The way to calculate 1 characteristic if you know the other 2. Tomorrow: Circuit types (Series vs. Parallel)

2. How you should be thinking about electric circuits: Voltage difference, voltage potential, or just voltage: a force that pushes the current through the circuit (in this picture, it would be equivalent to the height difference that forces the water to flow) Symbol = VUnits = volts (V)

3. A 12-V battery would be analogous to a 12-meter waterfall. A 6-V battery would be a 6-meter waterfall. A greater voltage is a greater “push” on the current.

4. Voltage is supplied by The CELL The cell stores chemical energy and transforms it to electrical energy when a circuit is connected. When two or more cells are connected together, we call this a Battery. The cell’s chemical energy is used up pushing electrons around a circuit.

5. Current: the actual “substance” that is flowing through the wires of the circuit (electrons!) How you should be thinking about electric circuits: Symbol = I Units = ampheres, amps (A)

6. What is a current? An electric current is a flow of electrons through wires and components. + - In which direction does the current actually flow? From the Negative terminal to the Positive terminal of a cell. (Think of where an electron would go if you released it near the battery.)

7. Check your understanding Use the diagram to complete the following statements: a. A current of one ampere is a flow of charge at the rate of _______ coulomb per second. b. When a charge of 8 C flows past any point along a circuit in 2 seconds, the current is ________ A. c. If 30 C of charge flow past point A in 10 seconds, then the current is _________ A. d. If the current at point B is 2.0 A, then the current at point D is ______. Consider this: Current = charge’s velocity So…Amps = Coulombs per second A = C/s

8. Check your understanding Use the diagram to complete the following statements: True or False: The current at point E is considerably less than the current at point A since charge is being used up in the light bulbs.

9. Resistance: friction that impedes flow of current through the circuit (like rocks in the river) How you should be thinking about electric circuits: Symbol = R Units = ohms (Ω)

10. Resistance Resistance is the hindrance to the flow of charge. For an electron, the journey around a circuit is not a direct route. Rather, it is a zigzag path that results from countless collisions with fixed atoms within the conducting material. The electrons encounter resistance - a hindrance to their movement. What do you think this does to the current? Will this have an effect on the total voltage?

11. Factors that affect resistance- First, the total length of the wires will affect the amount of resistance. The longer the wire, the more resistance that there will be. After all, if resistance occurs as the result of collisions between charge carriers and the atoms of the wire, then there is likely to be more collisions in a longer wire. More collisions mean more resistance. Second, the cross-sectional area of the wires will affect the amount of resistance. Wider wires have a greater cross-sectional area. Water will flow through a wider pipe at a higher rate than it will flow through a narrow pipe. In the same manner, the wider the wire, the less resistance that there will be to the flow of electric charge. A third variable that affects the resistance is what the material that a wire is made of. Not all materials are created equal in terms of their conductive ability. Some materials are better conductors than others and offer less resistance to the flow of charge. Silver is one of the best conductors but is never used in wires of household circuits due to its cost. Copper and aluminum are among the least expensive materials with suitable conducting ability to permit their use in wires of household circuits. For example…

12. simple circuits Here is a simple electric circuit. It has a cell, a lamp and a switch. To make the circuit, these components are connected together with metal connecting wires. cell lamp switch wires

13. Can you define the following terms? 1.Voltage 2.Current 3.Resistance What 3 things can affect resistance? Try answering the following questions without yesterday’s notes, and then check if you’re right.

14. simple circuits Closed Circuit- When the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around. Open Circuit- If there were any breaks in the circuit, the current could not flow.

15. circuit diagram cellswitchlampwires Scientists usually draw electric circuits using symbols;

16. More symbols: In circuit diagrams components are represented by the following symbols; cell battery switch lamp Ammeter (measures current) Voltmeter (measures voltage)

17. Ohm’s Law Georg Simon Ohm (1787-1854)- As a school teacher, Ohm began his research with the new electrochemical cell, invented by Italian scientist Alessandro Volta.Ohm electrochemical cellAlessandro Volta I= Current (Amperes, A) (amps) V= Voltage (Volts, V) R= Resistance (ohms, Ω)

18. Ohm’s Law Consider the formula to fill-in-the blank: The greater the battery voltage (i.e., electric potential difference), the ____________the current. And the greater the resistance, the ____________the current. Charge flows at the greatest rates when the battery voltage is ______and the resistance is __________. I = Current (Amps) V = Voltage (Volts) R = Resistance (ohms) Quick thought: Will Ohm’s Law work if there’s no resistance?

19. Practice Problems: 1. What is the current in a 10V circuit if the resistance is 2Ω? 2. What voltage is required to move 2A through 5Ω? 3.What is the resistance of a circuit with 20V and 2A? Ready to tackle some problems solo?