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## DC ELECTRICAL CIRCUITS

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**DC ELECTRICAL CIRCUITS**POWER**DC ELECTRICAL CIRCUITS**• Power is the rate at which electrical work is done in a specific amount of time. • Earlier you learned that a joule is equal to the amount of work done by one volt of EMF in moving one coulomb of charge with no regard to time. • Power is the measure of joules of work per unit of time, the unit of power is the Watt.**DC ELECTRICAL CIRCUITS**• The watt is equal to one joule per second. • The joule is equal to .738 foot pounds ( about ¾ of a pound), the watt is also equal to .738 foot pounds (one pound lifted one foot) of work per second.**DC ELECTRICAL CIRCUITS**• The unit of mechanical power is the horsepower, one horsepower is equal to 550 foot pounds per second, or 746 watts.**DC ELECTRICAL CIRCUITS**• Power is directly proportional to both current and voltage. • The symbol (P) is used to represent power in equations. • The formula for power is: P = I x E**DC ELECTRICAL CIRCUITS**• There are three formulas for every quantity in the expanded pie chart. • The center of the circle is the ohms law quantities; I, R, E & P, in this chart has its own color coded section.**DC ELECTRICAL CIRCUITS**• Here are the formulas to solve for amperage based on the values given. • If you have the wattage and voltage of a circuit, to solve for I which formula would you use?**DC ELECTRICAL CIRCUITS**• To solve for (R) you would use one of the three formulas in the pie chart depending on the values given. • P = 1000W, I = 5A what is the resistance?**DC ELECTRICAL CIRCUITS**• To solve for (E); • P = 200W, R = 25Ω, what is the voltage?**DC ELECTRICAL CIRCUITS**• To solve for (P); • E = 120V, R = 40Ω, what is the wattage?**DC ELECTRICAL CIRCUITS**• A HEATING UNIT IS RATED TO 1600 WATTS WHEN CONNECTED TO A 240 VOLT CIRCUIT, HOW MUCH CURRENT WILL THE UNIT DRAW?**DC ELECTRICAL CIRCUITS**• A CIRCUIT WITH A 100 OHM RESISTOR HAS A CURRENT OF 6.8 AMPS, WHAT IS THE VOLTAGE? • IS A RESISTOR RATED TO HALF A WATT LARGE ENOUGH FOR THIS CIRCUIT?**DC ELECTRICAL CIRCUITS**• Resistors are rated by wattage, and as you can see here the smaller the resistor the lower the wattage rating.**DC ELECTRICAL CIRCUITS**• As you know incandescent light bulbs are rated in wattage, fluorescent bulbs are also rated in wattage and now LED bulbs are becoming more and more popular. • Given that the voltage and current remain the same how do you select the right bulb for the desired illumination.