Chapter 6, Section 5

1. Chapter 6, Section 5 Electric Power: Load Limit

2. April 18, 2011HW: 6.5 PTG, pg. 641, 1-13, Due Wed • LO • Explain why fuses and circuit breakers are important safety devices. • SC • Define power, insulator, and conductor • Use the equation P=IV • Calcuate the power limit of a 120-V household circuit • Differentiate between a fuse and circuit breaker • Identify the need for the circuit breakers and fuses in a home • Do Now: • 6.4 Quiz • Write LO and SC on new left side page • WDYS/WDYT pg. 631 • Agenda: • Do Now • Investigate • Physics Talk

3. Investigate • #1-complete set up as shown. Answer #1a in your notebook

4. Investigate • #2-6 Teacher Demo • http://its-about-time.com/physics/videos.html

5. Investigate #2 • Why do you think the fuse blew? • Why did the circuit require multiple appliances to blow the fuse? • Can you develop a model that explains why the fuse behaves the way it does?

6. Remember: • Voltage is the #Joules per Coulomb (# pretzels per person) • Current is the # Coulombs per second (people per second) • Power is the #Joules per second (# Pretzels per second) • P=VI • Power=Voltage x Current P I V

7. Investigate #3-6 • Complete table in your notebook

8. Investigate #3-5 • Create table in your log

9. Investigate 3-6 • Based on your calculations, if I have a 30A circuit breaker, what combinations of appliances would be needed to pop the circuit breaker? • List at least 3 combinations with 3 or more appliances • What is the total current and total power that cause the circuit to break?

10. April 19, 2011HW: 6.5 PTG, pg. 641, 1-13, Due Wed • LO • Explain why fuses and circuit breakers are important safety devices. • SC • Define power, insulator, and conductor • Use the equation P=IV • Calcuate the power limit of a 120-V household circuit • Differentiate between a fuse and circuit breaker • Identify the need for the circuit breakers and fuses in a home • Do Now: • Explain how a circuit breaker works • Agenda: • Do Now • Physics Talk • Summary

11. 6.5 Physics Talk • What is Power? • The rate at which energy is transmitted, or the energy used in a given amount of time • Joules (pretzels) per second • Determines the brightness of a bulb

12. 6.5 Physics Talk • Examples • 1 Volt battery, 1 Amp • 1 Joule per Coulomb • Turned on for 30 Seconds… • 30 Joules left the battery • 2 Volt battery, 2 Amp current • 2 Joules per Coulomb • Turned on for 30 seconds • 120 Joules left the battery

13. 6.5 Physics Talk • What happens to power as you increase Voltage and Current? • What is the equation for power? • Power will increase • Brighter bulb! • P=VI • Units Watt (W) or J/s P I V

14. 6.5 Physics Talk • What is a fuse? • Device placed in an electrical circuit that melts when too much current (amps) flow through it. Breaks the circuit and doesn’t allow the parts of the circuit to get damaged. • Fuses must be replaced in order to restore the circuit to normal operation

15. 6.5 Physics Talk • What is a circuit breaker? • Devices place in an electrical circuit that operates like an automatic switch to open the circuit when too much current flows through. • Can be reset when the current is reduced.

16. 6.5 Physics Talk • What are conductors? • A material that current can move through easily • Metals are good conductors • Copper is a good conductor and used for electrical wires • Outer electrons are loosely bonded and can be easily shared • Very low resistance

17. 6.5 Physics Talk • What is an insulator? • Do not allow electric current to flow easily • Outer electrons are tightly bonded • Examples: air, glass, plastic, rubber, wood • Used to provide protection from danger amounts of current. (rubber coating on electrical wires) • Very high resistance!

18. 6.5 Physics Talk • How can you blow a fuse or trip a circuit breaker? • Devices that generate lots of heat also use lots of energy • Devices with high power ratings (require a lot of power) are responsible for blowing a fuse or tripping a circuit breaker. • Examples: Hair dryer, toaster, things that heat up.

19. 6.5 Physics Talk • What happened in our experiment? • As we added more appliances, you increased current (amps) until the fuse burned out. • This opened the circuit and current flow stops.

20. 6.5 Physics Talk • Why do we need fuses and circuit breakers? • Safety devices • Usually 15 A or 20 A, depending on the wires • Electrical current generates heat • Prevents wires from melting/starting fires

21. 6.5 Physics Talk • How does all this work in our houses? • Home circuits provide 120V • You can find the Power Rating (Watts) on most appliances • You can then calculate Current (amps)

22. How does this all work in our houses ?(con’t) • 100 W bulb is brighter than a 60 W bulb because the 100 W bulb will pull more current • 20 W compact florescent bulb produces the same amount of light as a 100 W conventional bulb but uses less power! This saves energy and money!

23. What are power limits? • Voltage of the circuits in your house are 120 V • Fuse/circuit breaker is 15A • That means the power limit is 120V x 15A=1800 W • If a toaster is 1200 W and a hair dryer is 1000W, they cannot operate on the same line since they total 2200 W. They would trip the circuit

24. What are current limits? • Voltage of the circuits in your house are 120 V • Fuse/circuit breaker is 15A • Appliances are wired in parallel, total current of the circuit will be the sum off all individual currents • If the total current in the circuit is greater than 15, the fuse will blow/circuit will trip.

25. Practice Problems • Pg. 637-638 • http://webs.rps205.com/curriculum/science/files/A3874CAB2CB74F2B9EEEF914DB22E2EA.pdf

26. Reflection • Essential Questions: Pg. 640 • What does it mean? • How do you know? • Why should you care? • LO and SC reflection