1. Electrical Calculations
Unit 10
Section 3

2. I. How are electric current, voltage, and resistance related?
a Ohm studied resistance and found that the ratio of voltage (V) to current (I) is a constant for all materials. The ratio is the resistance (R) of the material.
b R = V / I OR V = I x R
c. This means that as resistance goes up, current goes down. As resistance goes down, current goes up.

3. II. Electric Power
a. Electric power is the rate at which electrical energy is converted into other forms of energy. This is the current in your house.
b. We use this formula to find electric power:
Power = voltage x current OR
P = V x I

4. III. Watts and Kilowatts
a. Watts are a unit of power. The higher the wattage, the more energy that is used.
b. Kilowatts (kW) are another unit of power. One kilowatt is equal to 1,000 watts.

5. IV. Measuring Electrical Energy
a. The formula for finding electrical energy used in your home is:
Electrical energy = power x time OR
E = P x t

6. V. Electric Meters
a. Electric meters are used to determine how many kilowatt hours of energy are used in a house.
b. Example: If 2 kW of power are used for 3 h, the total amount of energy used is 6 kWh.

7. How to Save Energy
a. You can save energy by running appliances for less time, or by replacing old appliances with energy efficient appliances that use less energy.

8. Quickie Quiz Which of the following is Ohm’s law? E = P x t I = V x R
P = V x I
V = I x R

9. Quickie Quiz
2. How much electrical energy does a 40 W light bulb use if it is left on for 12 h?

10. 3. How many watts are in 10 kilowatts?
Quickie Quiz
3. How many watts are in 10 kilowatts?

11. Quickie Quiz
4. Circuit A has twice the resistance of Circuit B. The voltage is the same in each circuit. Which circuit has the higher current of electricity?