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Ohm’s Law and Electrical Power

Ohm’s Law and Electrical Power. Reminders. Resistance ( R ): “Electrical friction”, opposition to current Measured in ohms Current ( I): How fast the electricity is traveling Measured in amps. How do resistance( R ) & current (I) relate to each other?.

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Ohm’s Law and Electrical Power

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  1. Ohm’s Law and Electrical Power

  2. Reminders • Resistance ( R ): “Electrical friction”, opposition to current • Measured in ohms • Current ( I): How fast the electricity is traveling • Measured in amps

  3. How do resistance( R ) & current (I) relate to each other? • Inverse relationshipAs resistance increases, current decreasesAs resistance decreases, current increases

  4. Formulas for Ohm’s Law • Resistance = Voltage/ current • R = V/I • Voltage = Current X Resistance • V = I X R

  5. Practice Problems • A flashlight has 1.5 ohms of resistance and uses 5 amps of current. How many volts does the flashlight need? • 1. Write the equation V = I X R • 2. Fill in the numbers and units • V = 5 amps X 1.5 ohms • 3. Solve: • V = 7.5 volts

  6. Practice on Your Own • If a lightning bolt has 1000 ohms of resistance and a current of 150 A how much voltage of electricity does it have?

  7. Solved • 1. Write the equation V = I X R • 2. Fill in the numbers and units • V = 150 amps X 1000 ohms • 3. Solve: • V = 150,000 volts

  8. Electrical Power • The rate at which electrical energy is changed into other forms of energy • Formula for calculating power • Power = voltage X current • P = V X I • Unit for power is Watts (W) and Kilowatts (kW) • 1 kW = 1000 W

  9. Practice Problems • A toaster draws about 10 A of current. A home receives 120 V at each outlet. What is the power of the toaster? • 1. Write the equation P = V X I • 2. Fill in the numbers and units • P = 120 V X 10 A • 3. Multiply to solve: • P = 1,200 W

  10. Practice on Your Own • An overhead projector draws about 4.5 A of current from a 120 V outlet. What is the power needs for the overhead projector?

  11. Solved • P = V X I • P = 120 V X 4.5 A • P = 540 watts

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