2. OHM’S LAW Charge-volt-current-resistance Ohm’s law

3. Circuits An electric circuit is an external path that charges can follow between two terminals using a conducting material. For charge to flow, the path must be complete and unbroken. An example of a conductor used to form a circuit is copper wire. You can think of a wire as a pipe for charge to move through.

4. Charge  Charge- is measured in coulombs-(C)  1 COULOMB -AMOUNT OF ENERGY CARRIED BY 6.25 X10 8 ELECTRONS  Two kinds of charge positive and negative  Like charges repel and opposite charges attract  Charge is a basic property of matter  Electrical forces are forces between charges ie: static electricity

5. So do positive or negative charges flow through the circuit? Historically, positive charges were identified as the ones that flowed in the circuit. It was not until a later time that we understood that it was the negative charge (electrons) which were free to move. In reality, electrons flow from the negative terminal of the battery, through a conductor, to the positive terminal. This is the actual current. Circuits

6. Current While actual current is the flow of electrons from the negative terminal to the positive terminal, we use conventional current to model electric circuits. Conventional current is the flow of positive charges flowing from the positive to the negative terminal. Going forward, we will use conventional current to discuss electric circuits. Both conventional current and actual current lead to the same predictions but flow in opposite directions.

7. Current Th e letter "I" is the symbol for current. It is defined as the amount of charge that flows past a location in a conductor per unit time. ΔQ is the amount of charge, and Δt is the time it flowed past the location. ΔQ Δt I =

8. The current, has the units Coulombs per second. The units can be rewritten as Amperes (A). 1 A = 1 C/s Amperes are often called "amps". ΔQ Δt I = Current

9. CURRENT  Current(I) – measured in amperes or amps(A)  Current is the flow of charge  1 amp is the flow of 1 coulomb per second  current flows from plus to minus or high to low  charge is what actually flows in a wire not electrons  current carries energy and does work  a voltage difference (battery) supplies energy to make charges flow 

10. ALTERNATING CURRENT  In a DIRECT CURRENT (dc) circuit the current flows in one direction only. Normally batteries  In an ALTERNATING CURRENT (ac) circuit the direction of current flow through the circuit changes at a particular frequency (f). Flows in both directions Normally house  The frequency used in the United States is 60 cycles per second or 60Hz.

11. CURRENT http://www.youtube.com/watch?feature=pla yer_detailpage&v=8gvJzrjwjds

12. 1 12 C of charge passes a location in a circuit in 10 seconds. What is the current flowing past the point? answer

13. 2 A circuit has 3 A of current. How long does it take 45 C of charge to travel through the circuit? answer

14. Batteries Positive Terminal Negative Terminal A terminal is a conductor that allows for the movement of charge. Batteries convert chemical energy to electrical energy which maintains the potential difference. The chemical reaction acts like an escalator, carrying charge up to a higher voltage. Click here for a Battery Voltage Simulation from PhET

15. VOLTAGE  Voltage (V)– measure in Volts(V)- potential difference  Measure of energy in a circuit  Energy flows from high energy to low energy  Batteries add energy or voltage to a circuit  Voltage is reduced when energy is used  Bulbs and electric devices use energy

16. VOLTAGE  http://www.youtube.com/watch?v=g287MugJC9E http://www.youtube.com/watch?v=g287MugJC9E

17. Reviewing Basic Circuits The circuit cannot have gaps. The bulb had to be between the wire and the terminal. A voltage difference is needed to make the bulb light. The bulb still lights regardless of which side of the battery you place it on. W hat is going on in the circuit? What is the role of the battery?

18. The battery pushes current through the circuit. A battery acts like a pump, pushing charge through the circuit. It is the circuit's energy source. Charges do not experience an electrical force unless there is a difference in electrical potential (voltage).Therefore, batteries have a potential difference between their terminals. The positive terminal is at a higher voltage than the negative terminal. Batteries and Current How will voltage affect current? click here for a video from Veritasium's Derek on current

19. Conductors So me conductors "conduct" better or worse than others. Reminder: conducting means a material allows for the free flow of electrons. The flow of electrons is just another name for current. Another way to look at it is that some conductors resist current to a greater or lesser extent. We call this resistance, R. Resistance is measured in ohms which is noted by the Greek symbol omega (Ω) Click here to run another PhET simulation How will resistance affect current?

20. Current vs Resistance & Voltage Raising resistance reduces current. Raising voltage increases current. We can combine these relationships in what we call "Ohm's Law". Another way to write this is that: OR V = IR V R I = V I R = You can see that one Ω = V A click here for a Veritasium music video on electricity

21. Resistance –Ohm’s law  RESISTANCE – measure in Ohms (  )  low resistance – a lot of current flows  high resistance – a little current flows  Devices that use electrical energy have resistance  Light bulbs,TV Etc.   RESISTANCE = VOLTAGE  CURRENT   R= V  = V  I A 

22. RESISTANCE  The resistance of electrical devices ranges from very small (0.001 Ω) to very large (10×10 6 Ω).  Each device is designed with a resistance that allows the right amount of current to flow when connected to the voltage the device was designed for.

23. Resistance

24. OHM'S LAW TThe magnitude of the electric current that flows through a closed circuit depends directly on the voltage between the battery terminals and inversely to the circuit resistance. The relationship that connects current, voltage and resistance is known as OHM'S LAW and is written as follows:

25. OHM’ S LAW-  http://www.youtube.com/w atch?feature=player_detailp age&v=J4Vq-xHqUo8 http://www.youtube.com/w atch?feature=player_detailp age&v=J4Vq-xHqUo8

26. Current vs Resistance & Voltage Raising resistance reduces current. Raising voltage increases current. We can combine these relationships in what we call "Ohm's Law". Another way to write this is that: ORV = IR V R I = V I R = You can see that one Ω = V A click here for a Veritasium music video on electricity

27.  Ohm’s Law states – relationship between  Current (I) measured in amperes (A)  Voltage (V) measured in Volts(V) potential difference  Resistance (R )measured in Ohms( )   Ohm’s law  Current (amps) I = V – voltage (volts)  R- resistance (Ohms)   Can also be stated as V = I x R

29. 4 A flashlight has a resistance of 25 Ω and is connected by a wire to a 120 V source of voltage. What is the current in the flashlight? answer

30. 5What is the current in a wire whose resistance is 3 Ω if 1.5 V is applied to it? answer

31. 6 How much voltage is needed in order to produce a 0.70 A current through a 490 Ω resistor? answer

32. 7 What is the resistance of a rheostat coil, if 0.05 A of current flows through it when 6 V is applied across it? answer

33.  A BATTERY OPERATED CD PLAYER USES 12V FROM THE WALL SOCKET AND DRAWS A CURRENT OF 2.5 AMPS CALCULATE THE RESISTANCEOF THE CD PLAYER.

34. answer  12V/2.5= 4.8A  Work on problems