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Chapter 6, Section 5 . Electric Power: Load Limit. April 18, 2011 HW: 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

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chapter 6 section 5

Chapter 6, Section 5

Electric Power: Load Limit

april 18 2011 hw 6 5 ptg pg 641 1 13 due wed
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
investigate
Investigate
  • #1-complete set up as shown. Answer #1a in your notebook
investigate1
Investigate
  • #2-6 Teacher Demo
  • http://its-about-time.com/physics/videos.html
investigate 2
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?
remember
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

investigate 3 6
Investigate #3-6
  • Complete table in your notebook
investigate 3 5
Investigate #3-5
  • Create table in your log
investigate 3 61
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?
april 19 2011 hw 6 5 ptg pg 641 1 13 due wed
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
6 5 physics talk
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
6 5 physics talk1
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
6 5 physics talk2
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

6 5 physics talk3
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
6 5 physics talk4
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.
6 5 physics talk5
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
6 5 physics talk6
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!
6 5 physics talk7
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.
6 5 physics talk8
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.
6 5 physics talk9
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
6 5 physics talk10
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)
slide22

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!
slide23

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
slide24

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.
practice problems
Practice Problems
  • Pg. 637-638
  • http://webs.rps205.com/curriculum/science/files/A3874CAB2CB74F2B9EEEF914DB22E2EA.pdf
reflection
Reflection
  • Essential Questions: Pg. 640
    • What does it mean?
    • How do you know?
    • Why should you care?
  • LO and SC reflection