Electricity Chapter 17.3

Section 3 Electrical Calculations Ohm’s Law shows the relationship between resistance, voltage, and current. Ohm noticed that for each material the ratio between voltage and current was always the same.

Ohm’s Law Formula Resistance=Voltage/Current R=V/I OR Voltage= current x resistance V=I x R V R I

Ohm’s Law As voltage increases, current increases direct relationship As resistance increases, current decreases Inverse relationship Graphs on page 490 in you textbook illustrate these relationships

Electric Power Electric Power-the rate at which electrical energy is changed into other forms of energy The unit to measure power is the Watt (W). For larger numbers we use a kilowatt (kW) The brighter the light bulb is the more quickly it uses energy, therefore the more power it has.

Electric Power Formula Electrical Power= Voltage x Current P = V x I P V I

Measuring Electrical Energy You can save energy by using appliances with lower power ratings. The unit for energy is still the Joule (J) Often the power company will use Kilowatt-hour (kW-h) to measure the energy used. This makes sense, it is a unit of power x time and that equals energy.

Electrical Energy Formula Electrical Energy = power x time E = P x t E P t