What you need:

1
What you need

• Notebook
• Calculator
• Writing utensil

2
Ohms Law, Power, Energy
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Currents and Circuits

• Current - the flow of charged particles
• Circuit - a closed continuous path through which
  current flows
• - requires a voltage source to maintain the
  potential difference

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Ohms Law

• Resistance Voltage/ Current
• R V / I
• Units
• Resistance (R) ohms (O)
• Voltage (V) volt (V)
• Current (I) ampere (A)

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Ohms Law

• Increasing voltage increases resistance
• Increasing current decreases the resistance

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Resistors

• Any device that changes electrical energy into
  another form

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Example 1

• A 30.0 V battery is connected to a 10.0 O
  resistor. What is the current in the circuit?
• I V/R
• I 30.0 V / 10.0 O
• 3.00 A

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Power

• Measures the rate at which energy is transferred
• Power Current x Voltage
• P IV
• The unit of power is the Watt

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Example 2

• A 6.0 V battery delivers a 0.50 A current to an
  electrical motor. What power is consumed by the
  motor?
• P IV
• P (0.50 A)(6.0 V)
• P 3.0 W

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Electrical Energy

• Energy Power x time
• E Pt
• If you are using Watts, use seconds for time. In
  this case, energy is measured in Joules.

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Continue Example 2

• Using the information from the Example 2, how
  much electric energy is delivered if the motor
  runs for 5.0 minutes?
• E Pt
• E (3.0 W)(300 s)
• E 9.0 x 102 J

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The Kilowatt-Hour

• The joule (a watt-second) is a relatively small
  amount of energy too small for commercial sales
  use.
• For that reason, electric companies measure their
  energy sales in kilowatt-hours.

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The Kilowatt-Hour

• A kilowatt-hour is equal to 1000 watts delivered
  continuously for 3600 seconds (1 hour).
• 1 kWh (1000 J/s)(3600 s)
• 3.6x106 J

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Example 3

• A plasma tv draws 2 A when operated on 120 V.
• How much power does the tv use?
• If the tv is operated for an average of 7 hr/day,
  what energy in kWh does it consume per month (30
  days)?
• At 11 per kWh, what is the cost of operating the
  tv per month?