2.0- Transfer and Controlling Electrical Energy

1. 2.0- Transfer and Controlling Electrical Energy

3. A. Controlling Current Review: 1) What is the difference between current, voltage and resistance? 2) What are each measured in? Voltage – the energy of each electron Current – how fast the electrons are flowing Resistance – how much energy is stripped from the electrons; is how hard it is for electrons to flow

4. A. Controlling Current 3. What is the difference between an insulator and conductor? Insulators - Resist or preventsthe flow ofelectrons; tightly hold onto electrons Conductors –Allow the flow of e-; Electrons are not as tightly bound to the nucleus and are free to move

5. A. Controlling Current 4. What is the difference between: • Wet cell vs. dry cell? • Primary vs. secondary cell? • cell vs. battery • electrorefining and electrolysis? • Galvanizing and electroplating

6. A. Controlling Circuit • Review: • Insulators - Resists or prevents the flow ofelectrons • Electrons are tightly bound to the positive nucleus of the atoms

7. A. Controlling Current II. Conductors - Allow the flow of electrons • Electrons are not as tightly bound to the nucleus and are free to move

8. A. Controlling Current I. Resistors • Are conductors which provide SOME resistance (slowing) to the flow of electrons, in order to reduce current • Resistors will gain energy from each electron that passes through as light or heat

9. Ex. Tungsten light bulbs and space heaters are both resistors (light and heat are produced)

10. A. Controlling Current 1) Resistors • Every conductor resists the flow of electrons slightly so….. • The longer and thinner the wire, the higher the resistance is • The larger in diameter (thickness) the lower the resistance is

11. Draw a quick diagram to remember this by!

12. A. Controlling Current 2. Switches • Open and close a circuit to control current 3. Rheostat / Variable Resistor • Increase or decrease the current in a circuit by adjusting the resistance Ex. Volume control, Dimmer switches, thermostats

15. A .Controlling Current • Microelectronic circuits are tiny circuits found in microchips, iPod’s etc. • These use transistors, instead of switches to control the current.

16. B. Safety with Current

17. B. Safety with Current I. Current vs. Voltage • What should you be more concerned about…..current or voltage?? Why? Current – since it is how many electrons will be flowing through your body! A small current has a dramatic effect!

18. B. Safety with Current II. Safety Features • Circuit breakers – flip a switch if the current drawn from an appliance is too high • Fuses- melt causing an open circuit when current drawn is too high

19. Brainstorm…… How does an outlet work? Why are there 3 holes? Hint: Consider what a circuit needs in order for electricity to flow…

20. B. Safety with Current What is the purpose of a 3-pronged plug? Third prong supplies a ground wire to the building as a safety against a short circuit

21. C. Measuring Electricity I. Ohm’s Law • Relates current, voltage and resistance • As long as temperature is constant: • Resistance stays constant • Voltage and current are directly proportional ( V increases = I increases)

22. C. Measuring Electricity • Ohm’s Law R = V I V- voltage (V) I – current (A) R – resistance ()

23. Required Steps to Solving Problems 1. Write down what you know 2. Write down unknown 3. Choose formula 4. Substitute with units 5. Solve – make sure there are units!

24. C. Measuring Electricity Ex. What is the current of a circuit with a 9.0V battery and a 5  resistor?

25. C. Measuring Electricity • Ex. What is the resistance of a circuit with a 1.5 V battery which outputs 0.70A?

26. C. Measuring Electricity • Ex. What is the voltage of a circuit which has a resistance of 24  and current of 4.0A?

28. What is the resistance of this circuit? Hyperlink to practice qs.

29. C. Measuring Electricity II. Using Test Meters • Voltmeters – measure voltage drop across a circuit (connected in parallel ) • Ammeter – measures current by being connected in series • Galvonometers – test very small currents • Multimeter– tests multiple measurements such as voltage, current and resistance

30. Connected as an additional path in the circuit Connected in the same path as the circuit

31. D. Building/Analyzing Circuits Types of Circuits • Series – where only 1 path is present for electricity to flow Key Ideas: 1. If interrupted, the circuit will not work 2. Adding more loads causes: -an increase in total resistance -a decrease in current (but current is the same through each load) -Total voltage is the same, but drops over loads *Used in older Christmas lights - all lights go out when one goes out

32. Ex. Draw a series circuit with two lightbulbs that are controlled by the same switch. What happens to the brightness of the lights as you add more lightbulbs to the circuit?

33. D. Building/Analyzing Circuits 2) Parallel – where a separate path is present for each load/switch Key Ideas: 1. Circuit WILL work if interrupted (multiple paths) 2. Adding loads will not effect resistance 3. Adding loads draws higher current from the source (current is split between pathways) *House wiring is in parallel

34. Parallel vs. Series Circuit explained

35. Ex. Draw a picture of a circuit with two light bulbs that can be turned off and on separately from each other.

38. Ex. If both of the previous circuits have 100V sources, which would have the most resistance? The most current?

39. ACTIVITY: Connect a circuit with one source where two light bulbs (lamps) can be shut off independently of each other.

40. Build a circuit where a light switch can be turned on/off by either two switches (such in a room with two entry doors or a hallway).Draw a schematic diagram to represent this.

45. A. Controlling Current Try: Set up the following circuit. What occurs when both, one or no switches are closed?

46. http://www.youtube.com/watch?v=20Vb6hlLQSg creation of electricalenergy