Watt is a physical quantity that everyone has to deal with every day without even knowing it. What does it measure, when did it arise and by what formula can it be found? Let's find answers to all these questions.
What is watt
First of all, it is worth knowing the definition of this term. So, watt is a unit used in the International SI System.
It can be of three types:
- Mechanical.
- Electric.
- Thermal.
History of appearance
Watts were first used as a quantity to measure power in Great Britain in 1882. Before that, horsepower was in use, and their understanding differed in individual countries.
The inventor of this unit of measurement (watt) was the “father” of the industrial revolution - James Watt (sometimes spelled Watt). By the way, it was named after him. For this reason, both joule (named after the British scientist James Prescott Joule) and watt are always abbreviated with a capital letter - W (in English W).
Since 1960, the watt has been a unit of power used throughout the world. After all, it was then that he was recognized
Power formula
Having understood the definition and history of the appearance of the watt, it is worth finding out its formula. It looks like this: N = A/t. And this stands for work divided by time.
Sometimes, in order to find out the number of watts, a slightly different power formula is used: N = F x V. V in this example the desired quantity is calculated not using work and time, but using force and speed data.
In fact, the second formula is a kind of adaptation of the classic one. It is simply taken into account that work is equal to the derivative of force by distance (A = F x S), and speed is the quotient of distance divided by time (V = S/t). If we put all this data: we get the following example: N = F x S/t = F x V.
Watts, Volts and Amps
In addition to the formula discussed in the previous paragraph for searching for the physical quantity being studied, there is another one. It demonstrates the relationship between power (watts) and current (amps).
However, before you read it, it's worth learning a little more about these units of measurement.
Volt (V, in English V) is a unit of measurement of electrical voltage. In formulas it is denoted by the Latin letter U.
Ampere (A, also A in English) - a quantity characterizing force electric current, denoted by the letter I.
Formula for the relationship between power, voltage and current
Having briefly examined the features of all these quantities, we obtain this formula.
It looks like this: P = U x I. In it, P is power (watts), U is voltage (volts), I is current (amps).
If necessary, this formula can be simulated if the power is already known, but you need to find the current (I = P / U) or voltage (U = P / I).
At modern development technologies, in order to find out how many watts are contained in a certain number of amperes, you can simply find a specialized power calculation program on the Internet and enter the available data into it. This is not difficult to do; in any search engine you need to look for the phrase “calculator for converting watts to amperes”, and the system will give the addresses of the necessary sites.
Sub-unit W
Besides practical application, the units in question are often used to perform numerous theoretical calculations. However, if the power is extremely low, writing watts using decimals with many zeros is quite impractical. To facilitate this task, scientists introduced sub-multiple W units. They are usually written as degrees with a minus.
To date, a dozen of them have been identified, but in practice many of them are not used.
For example, the first two submultiple units of a watt: dW (deciwatt, equal to 10 -1 W) and cW (centiwatt, equal to 10 -2 W) are not recommended for use. But milliwatt (mW, equal to 10 -3), microwatt (μW, equal to 10 -6) and nanowatt (nW, equal to 10 -9 W) are some of the most used. And not only in calculations, but also in the manufacture of various measuring instruments.
For example, in medical devices such as electrocardiograph and electroencephalograph, the units of measurement are microwatts (µW).
In addition to those listed above, there are five more sub-multiple units: picowatt (10 -12), femtowatt (10 -15), attowatt (10 -18), zeptowatt (10 -21) and ioctowatt (10 -24). However, all of them are used in rare cases, and then only in theoretical calculations.
Multiple units of W
The unit itself is relatively small. For example, to wash one kilogram of laundry in one hour in an automatic washing machine class A++, you will need electricity. However, if you consider that on average about 3.5 kilograms of clothes are washed at the same time, this means that 525 W are consumed. And this is just one wash, but how many of them happen in a month or a year? Quite a lot, as well as the number of watts consumed. To make them easier to write, ten multiples of units are allocated based on W, written as powers.
As in the case of fractional values, the first two of them (decawatt - 10 1 and hectowatt - 10 2) are not usually used, so they exist only “de jure”.
It is worth noting that when writing abbreviations of multiple units, the first letters are often capitalized. This is done in order not to confuse megawatts (MW - 10 6) with microwatts (mW) and other similar quantities.
The most commonly used is the well-known kilowatt (kW). It is equal to a thousand watts (10 3). The second most popular is the aforementioned megawatt. This unit is most often used in the electrical power industry. Less commonly, it uses values such as gigawatts (GW - 10 9) and terawatts (TW - 10 12). For example, in one year on average, humanity consumes about 1.9 TW of electricity.
The remaining four quantities - petawatts (PW - 10 15), exawatts (EVt - 10 18), zettawatts (ZW - 10 21) and iotawatts (IW 10 24) - are very rarely used, mainly in theoretical calculations. For example, according to one of them, it is assumed that full power The energy emitted by the Sun is 382.8 IW.
Despite the many multiples and sub-multiples of the watt, it is not difficult to perform mathematical operations with them. The easiest way is to convert everything into watts and then perform operations with degrees.
Another simple way to find out watts (quantity when using large or small quantities associated with them) is to find an online calculator on the Internet. By the way, with its help you can even convert W into horsepower.
Watts and watt-hours
Having figured out what a unit of measurement a watt is (and also having learned its multiples and sub-multiple values and formulas for finding it), it is worth taking time to consider such a close concept as watt-hours (Wh). Although the names Watt and Wh are very similar, they represent slightly different concepts.
The second unit is used to measure the energy produced over a certain period of time (one hour).
To make the difference clearer, it is worth considering the operation of an ordinary electric kettle with a power of 2200 W. To prepare compotes for the winter, the housewife almost continuously heated water with it for one hour. During this time, the device used 2200 Wh. If a woman had taken a weaker 1100 W kettle, it would have boiled the same amount of liquid in two hours and would still have used the same 2200 Wh.
All electricity supplied to consumers is measured not in watts, but in watt-hours (usually in kilowatt-hours, also a ratio of one to a thousand). To confirm this, you can simply go to any house meter. Regardless of the country and manufacturer, the numbers (demonstrating the amount of electricity used) will be marked “kilowatt-hour” (kWh). It can also be in English: kilowatt-hour (kW⋅h).
Moreover, the power of any power plant that synthesizes it is measured in ordinary watts (kilowatts and megawatts).
Watt, according to the SI system, is a unit of measurement of power. Nowadays it is used to measure the power of all electrical and other devices.
James Watt and his universal steam engine.
What is Watt
This value was first proposed for measuring power in 1882. The name of the unit was given in honor of the famous English (and if by place of birth, then Scottish) inventor James Watt. One of the most famous scientists in the world, who created a universal steam engine by modifying Newcomen's machine. However, what brought him the greatest fame was the unit of measurement named after him. Before this, power was calculated in horsepower (hp), which, by the way, was proposed for use by Watt himself. In our time, hp. used primarily to measure power in automobiles only, although there are rare exceptions.
According to the theory of physics, power is the rate of energy consumption, expressed as a ratio of energy to time: 1 W = 1 J/1 s. One watt is equal to the ratio of one joule (a unit of work) to one second. Today, the unit of measurement kilowatt (abbreviated designation kW) is more often used to indicate the power of electrical appliances. It’s easy to guess how many watts are in a kilowatt - the prefix “kilo” in the SI system denotes the value obtained by multiplying by a thousand.
Below we recommend watching a simple and understandable video about the subject of our conversation; I think everything will become clear if you perceive information easier by hearing, and in any case, a video can be useful to reinforce the material.
Watts to kilowatts
That is, 1 kW = 1000 W (one kilowatt is equal to a thousand watts). The reverse translation is just as simple: you can divide the number by a thousand or move the decimal point three digits to the left. For example:
- power washing machine 2100 W = 2.1 kW;
- kitchen blender power 1.1 kW = 1100 W;
- electric motor power 0.55 kW = 550 W, etc.
Kilojoules to kilowatts and kilowatt-hours
Sometimes our readers are interested in how to convert kilojoules to kilowatts. To answer this question, let's return to the basic ratio of watts and joules: 1 W = 1 J/1 s. It's easy to guess that:
1 kilojoule = 0.0002777777777778 kilowatt-hour (there are 60 minutes in one hour, and 60 seconds in one minute, therefore there are 3600 seconds in an hour, and 1/3600 = 0.000277778).
1 W = 3600 joule per hour
Watts to horsepower
1 horsepower = 736 Watts, therefore 5 horsepower = 3.68 kW.
1 kilowatt = 1.3587 horsepower.
Watts to calories
1 joule = 0.239 calories, therefore 239 kcal = 0.0002777777777778 kilowatt-hour.
Not to be confused with kilowatt hour
Probably everyone has heard at least once in their life about such a unit as a kilowatt-hour (kWh). This unit measures the work done by the device per unit of time. In order to understand its difference from a kilowatt, let’s take the example of a home TV with a power consumption of 250 W. If you attach it to electric meter and turn it on, then exactly one hour later the meter will show that the TV has consumed 0.25 kW of electricity. That is, the TV consumption is 0.25 kWh. A device with such a consumption value, left on for 4 hours, will “burn”, respectively, 1 kW of energy. The daily consumption of a particular device depends on the features of its design, and sometimes it may turn out that the devices that seem the least “gluttonous” to us actually make up a larger share of the total electricity costs. So, for example, a regular TV has 4 times lower consumption compared to a 100 W incandescent lamp. In turn, electric kettle“burns” three times more light than such a light bulb. The average daily energy consumption of a personal computer is about 14 kW, and that of a refrigerator is up to 1.5 kW.
The international designation for watts is W, and in Russian it is “W”. Now this energy measurement parameter is widely used in various mechanisms - from household appliances to complex technical designs.
Story
The unit of measurement watt was named after the Scottish engineer who created a steam engine, the model of which he modified from Newcomen's invention.
Thus, it was adopted at the second congress of the scientific association in Great Britain in 1882. Until then, most energy calculations used horsepower, one metric unit of which equals approximately 735 watts.
Watt as a quantity in physics
To better understand what is measured in watts, you need to brush up on your school physics lessons and remember the definition of energy. A physical quantity that uses the SI unit joule (J) and is called energy. It is used as a general measure of the effectiveness of various thermal processes or interactions between objects and other phenomena occurring with matter - in science, nature, technology, etc.
That's what is measured in watts - power, which determines how much various objects consume or release energy. The speed of its transmission through objects and transformation of one form into another is also calculated. In other words, power, defined in watts, is equal to 1 unit of energy divided by 1 unit of time - a second:
- 1W=1J/1sec
Volts and watts
What is the difference between a volt and a watt? Voltage is calculated in volts. Let's say the voltage of the power source - battery, accumulator or network - must be equal to or deviate slightly (in%) from the voltage that is installed on the device - a lamp or complex electronic equipment.
What is measured in watts? The answer here is already clear - this is power, which can be calculated as energy consumed, for example, when choosing a kettle - it will heat up faster, but will consume more electricity. Or given the output power of, say, a speaker or amplifier, the higher the power, the wider the range and louder the sound. Watt is also indicated in motors internal combustion- cars, motorcycles, trimmers and other mechanisms. However, the horsepower measurement is often used for such engines in other countries.
Power of electrical appliances
Power household appliances measured in watts, which is usually specified by the manufacturer. Some devices, such as lamps, can set power limits so that if the cartridge becomes very hot, they do not fail. Which will limit the period of use. Typically, such problems arise with incandescent lamps. In Europe, for example, the use of these lamps was limited due to their high power.
LED lamps consume much less electricity, while the brightness of such a lamp is not inferior to incandescent lamps. For example, with an average brightness of 800 lumens, the energy consumption of an incandescent lamp, measured in watts, will be 60, and an LED lamp will be from 10 to 15 watts, which is 4-6 times less. Power fluorescent lamp- 13-15 watts. So, although the cost is higher, LED or fluorescent lighting is becoming more common because it lasts longer and is energy efficient.
The power of the device determines how much work it will produce and for how long, but it also determines how much energy will be consumed. On most household electrical appliances Power is written, for example, on teapots; power is also one of the characteristics of a car. But they are often measured in different units, which is why engineers have to switch between power measurement units when making calculations.
System units
Let's give a definition: in physics, power is understood as a quantity that characterizes the performance (speed of energy transfer or conversion) of mechanisms and devices. It is connected with another concept - work.
In mechanics, power is found using the formula:
$P = \frac (dA)(dt) = F \cdot v \cdot cos \alpha$, from which it follows that power is understood as work, measured in Joules, divided by the time of its execution in seconds.
Rice. 1. Work on moving cargo.
$P = \frac (dW)(dt)$, i.e. as the rate of change of energy of the system.
In electrodynamics, power has its own formula:
So the unit of power is Joules divided by second (Volts times Amps), or Watts. The last name was given in honor of the engineer James Watt, who created the steam engine. Watt is the SI unit of power.
In industry and on devices, larger units are often used - kilowatts, megawatts, etc. They are obtained by adding standard decimal prefixes. Accordingly, 1 kW = 1000 W, 1 MW = 1,000,000 W.
Rice. 2. Power on an electrical appliance.
In the CGS system (centimeter, gram, second), which has become widespread in electrodynamics, power is usually measured in ergs per second. $ 1 \: erg = 10^(-7) \: J $, then $ 1 \: Watt = 10^7 \: \frac (erg)(s) $
In the MKGSS system (meter, kilogram-force, second), power is measured in kilogram-force multiplied by meter and divided by s. $1 \: kgf = 10 \: N$, and then $1 \: Watt = 0.1 \: \frac (kgf \cdot m)(s)$
Non-system units
James Watt himself, whose name now denotes units of power, measured this parameter in horsepower. This happened historically: James compared how many horses it would take to do the same work that his steam engine did. 1 hp equal to the power that must be expended to lift a body weighing 75 kg at a speed of 1 m/s.
Now the unit of measurement that Watt used is understood as mechanical horsepower - 1 hp. = 745.7 W. But there are other types of hp. For example, in Russia they often use metric - one such hp. equal to 735.5 W. Sometimes electric (746 W), boiler (9809.5 W) and hydraulic (745.7 W) are used. They are all approximately equal, but depending on the area it is more convenient to use one or another horsepower.
In thermophysics and thermodynamics, other non-systemic units have become widespread - calories per second (cal/s). In the international standard, 1 calorie is 4.187 J. Calories, in particular, were the heat of combustion of fuel, the work required to heat water, and the energy obtained from food. From the above ratio it follows that 1 Watt is 0.24 calories. 4.6. Total ratings received: 137.
When choosing a hair dryer, blender or vacuum cleaner in a store, you will notice that on its front panel there are always numbers with the Latin letter W. Moreover, according to sellers, the higher its value, the better and faster this electrical appliance will perform its direct functions. Is this statement true? Perhaps this is another publicity stunt? How does W stand for, and what is this value? Let's find out the answers to all these questions.
Definition
The above letter is a Latin abbreviation for the quantity familiar to everyone from physics lessons - watt. According to the International SI Standards, Watt (W) is a unit of measurement of power.
If we return to the issue with the characteristics of household electrical appliances, then the higher the number of watts in any of them, the more powerful it is.
For example, on the display case there are two blenders with the same price: one of them is from a popular company with 250 W (W), the other is from a lesser-known manufacturer, but with a power of 350 W (W).
These numbers mean that the second one will chop or beat food faster than the first one over the same period of time. Therefore, if the buyer is primarily interested in the speed of the process, it is worth choosing the second option. If speed does not play a key role, you can purchase the first one, as it is more reliable and, possibly, durable.
Who came up with the idea of using watts?
Oddly enough it sounds today, but before the advent of watts, the unit of measurement of power almost throughout the world was horsepower (hp, in English - hb), less often foot-pound-force per second was used.
Watts were named after the man who invented and introduced this unit - Scottish engineer and inventor James Watt. Because of this, this term is abbreviated with a capital letter W (W). The same rule applies to any SI unit named after a scientist.
The name, like the unit of measurement itself, was first officially considered in 1882 in Great Britain. After this, it took watts a little less than a hundred years to be accepted throughout the world and become one of the units International system SI (this happened in 1960).
Formulas for finding power
From physics lessons, many remember various problems in which it was necessary to calculate the current power. Both then and today, the formula used to find watts is: N = A/t.
It was deciphered as follows: A is the amount of work divided by the time (t) during which it was completed. And if we also remember that work is measured in Joules, and time in seconds, it turns out that 1 W is 1 J/1 s.
The considered formula can be slightly modified. For this it is worth remembering the simplest scheme to find work: A = F x S. According to it, it turns out that work (A) is equal to the derivative of the force that performs it (F) by the path traveled by the object under the influence of a given force (S). Now, to find the power (watts), we combine the first formula with the second. It turns out: N = F x S /t.
Sub-unit watts
Having dealt with the question “Watts (W) - what is it?”, it is worth finding out what sub-multiple units can be formed based on the available data.
When making measuring instruments for medical purposes, as well as important laboratory research, it is necessary that they have incredible accuracy and sensitivity. After all, not just the result, but sometimes a person’s life depends on it. Such “sensitive” devices, as a rule, need little power - tens of times less than a watt. In order not to suffer with degrees and zeros, sub-unit watts are used to determine it: dW (deciwatts - 10 -1), sW (centiwatts - 10 -2), mW (milliwatts - 10 -3), µW (microwatts - 10 -6 ), nW (nanowatts -10 -9) and several smaller ones, up to 10 -24 - iW (ioctowatts).
An ordinary person does not encounter most of the above-mentioned submultiple units in everyday life. As a rule, only research scientists work with them. Also, these values appear in various theoretical calculations.
Watts, kilowatts and megawatts
Having dealt with submultiples, it is worth considering multiple units of watts. These are exactly what every person encounters quite often when heating water in an electric kettle, charging mobile phone or performing other daily “rituals.”
In total, today scientists have identified about a dozen such units, but only two of them are widely known - kilowatts (kW - kW) and megawatts (MW, MW - in in this case The capital letter “m” is used so as not to confuse this unit with milliwatts (mW).
One kilowatt is equal to a thousand watts (10 3 W), and one megawatt is equal to a million watts (10 6 W).
As in the case of fractional units, among multiples there are special ones that are used only in narrow-profile enterprises. Thus, power plants sometimes use GW (gigawatts - 10 9) and TW (terawatts - 10 12).
In addition to the above, petawatts (PW - 10 15), exawatts (EVt - 10 18), zettawatts (ZW - 10 21) and iotawatts (IW - 10 24) are distinguished. Like especially small submultiples, large multiples are used mainly in theoretical calculations.
Watt and watt-hour: what is the difference?
If on electrical appliances power is indicated by the letter W (W), then when looking at a regular household electricity meter you can see a slightly different abbreviation: kW⋅h (kWh). It stands for "kilowatt-hour".
In addition to them, watt-hours (Wh - W⋅h) are also distinguished. It is worth noting that according to international and domestic standards, such units in abbreviated form are always written only with a dot, and in the full version - with a dash.
Watt hours and kilowatt hours are different units from W and kW. The difference is that with their help it is not the power of transmitted electricity that is measured, but the electricity itself. That is, kilowatt-hours show exactly how much of it was produced (transmitted or used) per unit of time (in this case, one hour).
