# Currents and Circuits - Midland Independent School District

What you need: Notebook Calculator Writing utensil Ohms Law, Power, &

Energy 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 Ohms Law Resistance = Voltage/ Current R = V / I Units Resistance (R) = ohms ()

Voltage (V) = volt (V) Current (I) = ampere (A) Ohms Law Increasing voltage increases resistance Increasing current decreases the resistance

Resistors Any device that changes electrical energy into another form Example #1: A 30.0 V battery is connected

to a 10.0 resistor. What is the current in the circuit? I = V/R I = 30.0 V / 10.0 = 3.00 A Power Measures the rate at which

energy is transferred Power = Current x Voltage P = IV The unit of power is the Watt 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 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. 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

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 kilowatthours.

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 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?

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