This document discusses power in single path DC circuits. It defines power as the rate at which energy is converted, measured in watts. It explains that power ratings indicate how quickly a device converts energy. Formulas show that power is equal to voltage times current or current squared times resistance. Heat produced during energy conversion can cause problems for some devices like motors and transformers but not others like lamps. Examples are provided for calculating current drawn with different voltages and resistances.

1. UEENEEE003B Solve Problems in Single Path DC Circuits Power

2. Power Power is the RATE that energy is converted.(unit watts W) Or Power is a measure of the amount of energy converted in 1 second. The POWER RATING of a device tells the rate that energy is converted: 75W lamp 750kW motor 8/9/2011 Revision02 2

3. 8/9/2011 Revision02 3 Formula for PowerP =V x IP = V2RP =I2R

4. During the conversion some input energy(electrical) is changed to heat within the device. The heating of the electrical device may produce a problem: motors transformers cables In other electrical devices this is rarely a problem: lamps 8/9/2011 Revision02 4 Power cont.

5. Your turn to think What would the current be if the voltage is increased to 3V? What would the current be if the voltage is increased to 10V? What would the current be if the resistance is increased to 2W (V = 1V) 8/9/2011 Revision02 5

6. Calculate the current drawn for a car battery. Allow 140W for the spark and pump. Allow 100W for the radio and dash panel. Allow 96W for the alternator field. Allow for: head lights (low and high beam) tail lights park lights 8/9/2011 Revision02 6