Watt
The watt (W) is the SI unit for measuring power, which is defined as the rate of work done or energy transferred over time. One watt is equivalent to one joule of energy transferred per second. This derived unit is named after the Scottish engineer James Watt, noted for his significant enhancements to the steam engine. Wattage is commonly utilized to indicate the power consumption of electronic devices, with each device having a specific power rating that denotes the maximum wattage it can safely use without damage.
In electrical systems, power generation involves the movement of electrons, which flow between atoms along conductive materials, such as copper wires, driven by a potential difference, such as that provided by a battery. The relationship between current, voltage, and resistance is described by Ohm's law. Understanding wattage is crucial in modern electronics, particularly for high-performance devices with sensitive components, and is increasingly relevant as society becomes more dependent on electric power.
Watt
FIELDS OF STUDY: Classic Mechanics
ABSTRACT: The watt is the standard unit for measuring power, which is defined as work or energy transfer over time. One watt is equivalent to one joule of energy transferred or consumed per second. Everyday appliances such as toasters use wattage to indicate the power needed to operate the device, the power it outputs, or the maximum power it can utilize without damage.
PRINCIPAL TERMS
- derived unit: a unit created by combining two or more other units.
- displacement field: in electrodynamics, the electric field produced solely by free charges (e.g., free electrons).
- International System of Units (SI): a standardized set of units and measures used by scientists worldwide, based on and largely synonymous with the metric system.
- joule: the SI derived unit of energy, work, or heat.
- Ohm’s law: an empirical law stating that the current, or flow of electrical charge, between two points is directly proportional to the voltage, or difference in electric potential, between those points.
- power: the work done or energy transferred over time.
- power rating: the maximum electrical power a device can use without being damaged.
- revolution: describes circular motion wherein an object circles an internal axis (e.g. the moon spinning about its axis); contrast to rotation, wherein the axis is external (e.g. the moon orbiting the earth).
Quantifying Energy Transfer over Time
Watts (W) are the International System of Units (SI) unit for measuring power—that is, work done or energy transferred over time. The power rating of a device indicates the maximum wattage it can use without damage. One watt is equivalent to one joule (J) of energy transferred per second. Because it is based on a combination of two or more SI units, the watt is considered a derived unit. It is named after Scottish engineer James Watt (1736–1819), who famously developed radical improvements to the steam engine. Wattage is most commonly used to indicate the energy consumption of electronics.
How Electrical Power Is Generated
Electrical power is generated by the transfer of electrical energy, usually in the form of electrons, between atoms. Electrons flow down the atoms of a copper wire because there is a large difference between the electric potential of the source (e.g., a battery) and that of the destination (e.g., a light bulb). The energy carried by the electrons is either transferred or transformed in order to do work. An incandescent bulb works by transforming the energy carried by the electrons into light, which is a form of electromagnetic energy. The electric field generated by free electrons and other free charges moving through conductive materials is called a displacement field.
Calculating Wattage
Electric current, or the rate at which electric charge is transferred across a material, obeys Ohm’s law, named after German physicist Georg Ohm (1789–1854). The SI unit of electrical resistance, the ohm (Ω), is also named after him. Ohm’s law states that current (I) is directly proportional to the voltage (V), or difference in electrical potential across the material, divided by the resistance (R) of that material:
The term "wattage" simply means power (P) as measured in watts. Power can be expressed a variety of ways:
Given a nine-volt battery connected to itself by a loop of copper wire with a resistance of eighteen ohms, one can determine the amount of electrical power produced by the battery sending a current through the wire:
Wattage Today
Wattage is a vital parameter in the design and use of high-performance electronics, which often have very sensitive components. Understanding wattage and its relationship to voltage and resistance will only become more useful in an increasingly electric world.
Bibliography
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Gibilisco, Stan. Electricity Demystified. 2nd ed. New York: McGraw, 2012. Print.
Henderson, Tom. "Ohm’s Law." The Physics Classroom. Physics Classroom, n.d. Web. 1 June 2015.
Hughes, John M. Practical Electronics: Components and Techniques. Sebastopol: O’Reilly, 2015. Print.
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