Power & Energy

Power

IVPsecond / Joule (W) Watt :in Measured

-Rate at which energy is used or alternatively, the rate at which work

is done.

•Using Ohm’s Law, you can state the above formula in a number of ways:

P = I2 * RP = V2 / R

Energy• Energy is the fundamental capacity to do

work.• Note that energy can neither be created

or destroyed, only transformed.• Energy is the amount of power

consumed over time

Energy

Energy (E) lost or gained by any system is determined by:

E = Pt

Since power is measured in watts (or joules per second) and time in seconds, the unit of energy is the watt-second (Ws) or joule (J)

Going Back to Power

tW

P

second / joule 1 (W)Watt 1

Power is an indication of how much work (the conversion of energy from one form to another) can be done in a specific amount of time; that is, a rate of doing work.

Example:• Two resistance of 10 and 15 ohms,

each connected in parallel. The two are then connected in series with a 5 ohm resistance. If then connected across a 12 volt battery. What are the current and power?