What's the difference between amps and watts?

amps, volts, watts.

• I am confused about what exactly wattage is. ON THIS PAGE: http://science.howstuffworks.com/electricity3.htm IT SAYS: In an electrical circuit, the number of electrons that are moving is called the amperage or the current, and it is measured in amps. The "pressure" pushing the electrons along is called the voltage and is measured in volts. ... 1 amp physically means that 6.24 x 10^18 electrons move through a wire every second, and the voltage is the amount of pressure behind those electrons. ON THIS PAGE: http://science.howstuffworks.com/electricity5.htm IT SAYS: Volts * Amps = Watts ON THIS PAGE: http://science.howstuffworks.com/electricity6.htm IT SAYS: Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden. What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow. As I understand it, this is saying that if you double voltage (and resistance is the same) you also double the current. And, since volts * amps = watts - doubling both volts and amps, increases the watts by 4 times. How is this possible if you are only doubling voltage and resistance dosen't change? I assume there is a missing element here, like maybe I'm not accounting for any load. Or maybe the amount of current drawn has an inverse affect on the voltage, so that voltage only remains doubled if the current remains the same, and voltage actually drops some as the current increases, such that wattage remains only doulbed. Is there a good example, such as with water hoses, that can illustrate the difference between current and wattage?

• Answer:

  Hi paulshanks!! Simple mathematics can help you to understand this. Let me start with the Ohm's law: "The potential difference (voltage) across an ideal conductor is proportional to the current (amperage) through it. The constant of proportionality is called the "resistance", R. Ohm's Law is given by: V = I.R" Note: if you doubled V and R remains constant, to mantain the equality I must double also. To find any one of the three variables if the other two are known you can manipulate the original equation. The three forms of the Ohm's law are: 1) V = I.R 2) R = V/I 3) I = V/R You also know that the formula to calculate Power is: P = V.I = = V.(V/R) = by eq. 3) = V^2.R So if V is doubled and R remains constant, then P increases 4 times. See the following to understand the difference between current and power: "In electricity, current is the rate of flow of electrons, usually through a metal wire or some other electrical conductor." From "Current (electricity) - Wikipedia": http://en.wikipedia.org/wiki/Current_(electricity) Current is the flow of charge and the unit of current is the ampere. We say that the current in a conductor is one ampere when a charge of one coulomb passes through a cross section of the conductor each second. From this definition I = Q/t (amount of charge over time...) [a] "The potential difference is defined as the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the amount of work that unit charge flowing from the first point to the second can perform." From "Potential difference - Wikipedia": http://en.wikipedia.org/wiki/Electric_Potential_Difference#Electrical_definitions From this definition V = W/Q (amount of work per charge...) [b] "Power is a measure of how much work can be performed in a given amount of time. Work is generally defined in terms of the lifting of a weight against the pull of gravity. The heavier the weight and/or the higher it is lifted, the more work has been done. Power is a measure of how rapidly a standard amount of work is done... The power of a mechanical engine is a function of both the engine's speed and it's torque provided at the output shaft... Neither speed nor torque alone is a measure of an engine's power. A 100 horsepower diesel tractor engine will turn relatively slowly, but provide great amounts of torque. A 100 horsepower motorcycle engine will turn very fast, but provide relatively little torque. Both will produce 100 horsepower, but at different speeds and different torques... In electric circuits, power is a function of both voltage and current... In this case, however, power (P) is exactly equal to current (I) multiplied by voltage (E), rather than merely being proportional to IE. When using this formula, the unit of measurement for power is the watt, abbreviated with the letter "W". It must be understood that neither voltage nor current by themselves constitute power. Rather, power is the combination of both voltage and current in a circuit. Remember that voltage is the specific work (or potential energy) per unit charge, while current is the rate at which electric charges move through a conductor. Voltage (specific work) is analogous to the work done in lifting a weight against the pull of gravity. Current (rate) is analogous to the speed at which that weight is lifted. Together as a product (multiplication), voltage (work) and current (rate) constitute power. Just as in the case of the diesel tractor engine and the motorcycle engine, a circuit with high voltage and low current may be dissipating the same amount of power as a circuit with low voltage and high current. Neither the amount of voltage alone nor the amount of current alone indicates the amount of power in an electric circuit." Extracted from "An analogy for Ohm's Law - Chapter 2: OHM'S LAW - Volume I - DC": http://www.allaboutcircuits.com/vol_1/chpt_2/2.html Then P = W/t (power is defined as the rate at the work W is done) [c] Combining [a], [b] and [c]: P = W/t = (V.Q)/t = V.(Q/t) = V.I --------------------------------------------------------- For additional references see the followings pages: At "Basic Car Audio Electronics" you will find nice pages with examples, visit the pages 3 through 13 at the directory to the right of this page: http://www.bcae1.com/ PHYSCHEM: At this site visit the following modules: "Resistors and Ohm's Law": http://www.physchem.co.za/Current%20Electricity/Resistors.htm "Heating effects of currents": http://www.physchem.co.za/Current%20Electricity/Heating.htm "Ohm's Law" at the12volt.com: http://www.the12volt.com/ohm/ohmslaw.asp "Energy Through Our Lives - 3. Watts, Volts, and Amps, Oh My!": http://www.uwsp.edu/cnr/wcee/keep/Mod1/Flow/watts2.htm ---------------------------------------------------------- Search strategy: ohm law watt "electric power" watt current I hope that this helps you. If you find something unclear or incomplete, fell free to request for an answer clarification. I will gladly give you further assistance on this topic if you need it. Best regards. livioflores-ga