![]() For example, in an open-circuit condition, voltage is present but there is no current flow I = 0 (zero), therefore V*0 is 0 so the power dissipated within the circuit must also be 0. Power within an electrical circuit is only present when BOTH voltage and current are present. To help us understand the the relationship between the various values a little further, we can take all of the Ohm’s Law equations from above for finding Voltage, Current, Resistance and of course Power and condense them into a simple Ohms Law pie chart for use in AC and DC circuits and calculations as shown. So for example, a two-horsepower motor has a rating of 1492W, (2 x 746) or 1.5kW. The relationship between horsepower and watts is given as: 1hp = 746W. A light bulb converts electrical energy into both light and heat.Īlso, we now know that the unit of power is the WATT, but some electrical devices such as electric motors have a power rating in the old measurement of “Horsepower” or hp. So for example, an electrical motor will covert electrical energy into a mechanical force, while an electrical generator converts mechanical force into electrical energy. For example, a 1/4W resistor, a 100W light bulb etc.Įlectrical devices convert one form of power into another. Electrical Power RatingĮlectrical components are given a “power rating” in watts that indicates the maximum rate at which the component converts the electrical power into other forms of energy such as heat, light or motion. But if the calculated power is negative, (–P) in value the component produces or generates power, in other words it is a source of electrical power such as batteries and generators. If the calculated power is positive, (+P) in value for any formula the component absorbs the power, that is it is consuming or using power. So we can see that there are three possible formulas for calculating electrical power in a circuit. Then by using Ohm’s law and substituting for the values of V, I and R the formula for electrical power can be found as: To find the Power (P) ![]() Prefixes are used to denote the various multiples or sub-multiples of a watt, such as: milliwatts ( mW = 10 -3W) or kilowatts ( kW = 10 3W). The quantity symbol for power is P and is the product of voltage multiplied by the current with the unit of measurement being the Watt ( W ). The higher their value or rating in watts the more electrical power they are likely to consume. Light bulbs and heaters for example, absorb electrical power and convert it into either heat, or light, or both. A source of energy such as a voltage will produce or deliver power while the connected load absorbs it. ![]() Electrical Power in CircuitsĮlectrical Power, ( P ) in a circuit is the rate at which energy is absorbed or produced within a circuit. Any Electrical device or component that obeys “Ohms Law” that is, the current flowing through it is proportional to the voltage across it ( I α V ), such as resistors or cables, are said to be “Ohmic” in nature, and devices that do not, such as transistors or diodes, are said to be “Non-ohmic” devices. Then by using Ohms Law we can see that a voltage of 1V applied to a resistor of 1Ω will cause a current of 1A to flow and the greater the resistance value, the less current that will flow for a given applied voltage.
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