In 1882, the British Science Association decided to start using a new unit of measure called the watt. What is it used for today, what is it equal to and by what formula can it be calculated? Let's find answers to all these questions.

Watt is a unit of what?

Starting from that fateful year, when the British introduced the tradition of using the watt, gradually the whole world began to switch to it, instead of obsolete and impractical horsepower. With the advent of the SI system, it was introduced into it and began to be used everywhere.

So, what physical quantity has a unit of measure "watt"? Recall the lessons of physics: the correct answer to this question is power.

The watt got its name in honor of its "father" - the Scot James Watt. In abbreviation, this unit is always written with a capital letter - W (W - according to the international standards of the SI system), and in full - with a small "watt" (watt).

Being not a basic, but a derived unit (according to the SI standard), the unit in question is dependent on the meter, kilogram and second. In practice, this means that one watt is the power at which one joule of work is done in one second of time. That is, the following dependence is obtained: 1W \u003d 1J / 1s \u003d 1N x m / s \u003d kg x m 2 / s 3 \u003d kg x m 2 x s -3.

In addition to those listed above, the watt is associated with non-system units. For example, with calories. So 1 W = 859.845227858985 cal/hour. This ratio is important when it comes to calculating the amount of heat generated by an electric heater.

Formula

So watt is a unit of power. Let's look at the formula by which it can be calculated.

As mentioned above, power depends on work and time. The following formula is obtained: P = A / t (power is equal to the quotient of dividing the work by the time).

Knowing that the work formula is: A \u003d F x S (where F is force, S is distance), you can use these data.

As a result, we obtain the formula: P \u003d F x S / t. And since S / t is the speed (V), then the power can also be calculated like this: P \u003d F x V

Interdependence of ampere, watt, volt

The unit of measurement that we are considering is in direct relation to such quantities as voltage (measured in volts) and current strength (measured in amperes).

1 watt is constant power electric current at a voltage of 1 V and a power of 1A.

In the form of a formula, it looks like this: P \u003d I x U.

Watts, kilowatts, megawatts and microwatts

Having learned that a watt is a unit of power, on what quantities it depends, and by what formulas it is easier to calculate it, you should pay attention to such concepts as kilowatts, megawatts and microwatts.

Since W is a very modest value (such is the transmitter power of any mobile phone), in the field of electric power industry, it is more common to use kilowatts (kW).

Judging by the prefix “kilo”, standard for the SI system, we can conclude that 1 kW \u003d 1000 W \u003d 10 3 W. Therefore, to convert watts to kilowatts, you just need to divide their number by a thousand, or vice versa, if kilowatts are converted to watts.

For example, a typical passenger car has a power of 60,000 watts. To translate this into kilowatts, you need to divide 60,000 by 1000 and the result is 60 kW.

Kilowatts are a common unit for measuring electrical power. In this case, a large multiple of the watt unit is sometimes used. We are talking about megawatt - MW. It is equal to 1,000,000 watts (10 6) or 1000 kilowatts (10 3).

For example, the British Eurostar electric train has a capacity of 12 megawatts. That is, it is 12,000,000 watts. No wonder it is the fastest in the UK.

Despite its modest size, sometimes this unit turns out to be too large for measuring the power of certain objects, therefore, along with multiples in the C system, submultiple watt units are distinguished. The most commonly used of these is the microwatt (µW is lowercase to avoid confusion with the megawatt). It is equal to one millionth of a watt (10 -6). Usually this unit is used when calculating the power of electrocardiographs.

In addition to the three above, there are about two dozen other multiples and submultiples of the watt. However, most often they are used in theoretical calculations, and not in practice.

watt hour

Considering the features of the watt (a unit of power), let's pay attention to the watt-hour (Wh). This term is used to measure such a quantity as energy (sometimes work is measured in watt-hours).

1 watt hour equal to the number work done in one hour at a power of 1 watt.

Since the unit in question is rather small, the kilowatt-hour (kWh) is more commonly used to measure electricity. It is equal to 1000 watt-hours or 3600 Ws.

Please note that the power generated by power plants is measured in kilowatts (sometimes megawatts), but for consumers, its amount is calculated in kilowatt-hours (less often in megawatt-hours when it comes to megacities or huge enterprises).

Please note that in addition to kilowatt-hours and megawatt-hours, watt-hours have exactly the same multiples and submultiples as a regular watt.

What device is called a wattmeter

Comparing the definition of a watt (a unit of power) and a watt-hour (a unit of energy or work), pay attention to such a device as a wattmeter (wattmeter, wattmeter). It is used to measure the active power of electric current.

A classic device of this kind consists of four contacts, two of which are used to connect the wattmeter to an electrical circuit in series with that part of it, the power consumption of which is currently being measured. The remaining two contacts are connected in parallel to it.

Wattmeters are usually created on the basis of electrodynamic mechanisms.

In order to drag 10 bags of potatoes from a vegetable garden located a couple of kilometers from the house, you will need to rush back and forth with a bucket all day. If you take a cart designed for one bag, you can do it in two to three hours.

Well, if you throw all the bags into a horse-drawn cart, then in half an hour your crop will safely migrate to your cellar. What is the difference? The difference is in the speed at which work is done. The speed of mechanical work is characterized by a physical quantity studied in the seventh grade physics course. This quantity is called power. Power shows how much work is done per unit of time. That is, to find the power, it is necessary to divide the work done by the time spent.

Formula for calculating power

And in this case, the power calculation formula takes the following form: power \u003d work / time, or

where N is power,
A - work,
t - time.

The unit of power is the watt (1W). 1 W is the power at which 1 joule of work is done in 1 second. This unit is named after the English inventor J. Watt, who built the first steam engine. It is curious that Watt himself used a different unit of power - horsepower, and the power formula in physics in the form in which we know it today was introduced later. The measurement of horsepower is still used today, for example, when talking about the power of a car or truck. One horsepower equals approximately 735.5 watts.

Application of power in physics

Power is the most important characteristic of any engine. Various engines develop perfectly different power. It can be either hundredths of a kilowatt, for example, an electric shaver engine, or millions of kilowatts, for example, a launch vehicle engine. spaceship. With different load car engine produces different power to keep moving at the same speed. For example, with an increase in the mass of the load, the weight of the car increases, respectively, the friction force on the road surface increases, and in order to maintain the same speed as without the load, the engine will have to do more work. Accordingly, the power generated by the engine will increase. The engine will consume more fuel. This is well known to all drivers. However, at high speed, the inertia of the moving vehicle also plays a significant role. vehicle, which is the greater, the greater its mass. Experienced truck drivers find the best combination of speed and gasoline consumption so that the car burns less fuel.

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Initial value

Converted value

watt exawatt petawatt terawatt gigawatt megawatt kilowatt hectowatt decawatt deciwatt centiwatt milliwatt microwatt nanowatt picowatt femtowatt attowatt horsepower horsepower metric horsepower boiler horsepower electric horsepower pumping horsepower horsepower (German) int. thermal unit (IT) per hour Brit. thermal unit (IT) per minute Brit. thermal unit (IT) per second Brit. thermal unit (thermochemical) per hour Brit. thermal unit (thermochemical) per minute Brit. thermal unit (thermochemical) per second MBTU (international) per hour Thousand BTU per hour MMBTU (international) per hour Million BTU per hour ton of refrigeration kilocalorie (IT) per hour kilocalorie (IT) per minute kilocalorie (IT) per second kilocalorie (thm) per hour kilocalorie (thm) per minute kilocalorie (thm) per second calorie (thm) per hour calorie (thm) per minute calorie (thm) per second calorie (thm) per hour calorie (thm) per minute calorie (thm) per second ft lbf per hour ft lbf/minute ft lbf/second lb-ft per hour lb-ft per minute lb-ft per second erg per second kilovolt-ampere volt-ampere newton-meter per second joule per second exajoule per second petajoule per second terajoule per second gigajoule per second megajoule per second kilojoule per second hectojoule per second decajoule per second decijoule per second centijoule per second millijoule per second microjoule nanojoule per second picojoule per second femtojoule per second attojoule per second joule per hour joule per minute kilojoule per hour kilojoule per minute Planck power

More about power

General information

In physics, power is the ratio of work to the time during which it is performed. Mechanical work is a quantitative characteristic of the action of a force F on the body, as a result of which it moves a distance s. Power can also be defined as the rate at which energy is transferred. In other words, power is an indicator of the machine's performance. By measuring the power, you can understand how much and how fast the work is done.

Power units

Power is measured in joules per second, or watts. Along with watts, horsepower is also used. Before the invention of the steam engine, the power of engines was not measured, and, accordingly, there were no generally accepted units of power. When the steam engine began to be used in mines, engineer and inventor James Watt began to improve it. In order to prove that his improvements made the steam engine more productive, he compared its power to the working capacity of horses, since horses have been used by people for many years, and many could easily imagine how much work a horse can do in a certain amount of time. In addition, not all mines used steam engines. On those where they were used, Watt compared the power of the old and new models of the steam engine with the power of one horse, that is, with one horsepower. Watt determined this value experimentally, observing the work of draft horses at the mill. According to his measurements, one horsepower is 746 watts. Now it is believed that this figure is exaggerated, and the horse cannot work in this mode for a long time, but they did not change the unit. Power can be used as a measure of productivity, as increasing power increases the amount of work done per unit of time. Many people realized that it was convenient to have a standardized unit of power, so horsepower became very popular. It began to be used in measuring the power of other devices, especially vehicles. Even though watts have been around for almost as long as horsepower, horsepower is more commonly used in the automotive industry, and it's clearer to many buyers when a car's engine power is listed in those units.

Power of household electrical appliances

Household electrical appliances usually have a power rating. Some lamps limit the power of the bulbs that can be used in them, for example, no more than 60 watts. This is because higher wattage bulbs generate a lot of heat and the bulb holder can be damaged. And the lamp itself at a high temperature in the lamp will not last long. This is mainly a problem with incandescent lamps. LED, fluorescent and other lamps generally operate at lower wattage at the same brightness and if used in luminaires designed for incandescent lamps there are no wattage problems.

The greater the power of the electrical appliance, the higher the energy consumption and the cost of using the appliance. Therefore, manufacturers are constantly improving electrical appliances and lamps. The luminous flux of lamps, measured in lumens, depends on the power, but also on the type of lamps. The greater the luminous flux of the lamp, the brighter its light looks. For people, it is high brightness that is important, and not the power consumed by the llama, so recently alternatives to incandescent lamps have become increasingly popular. Below are examples of types of lamps, their power and the luminous flux they create.

• 450 lumens:
• Incandescent lamp: 40 watts
• Compact fluorescent lamp: 9-13 watts
• LED lamp: 4-9 watts
• 800 lumens:



• Incandescent lamp: 60 watts
• Compact fluorescent lamp: 13-15 watts
• LED lamp: 10-15 watts
• 1600 lumens:
• Incandescent lamp: 100 watts
• Compact fluorescent lamp: 23-30 watts
• LED lamp: 16-20 watts

From these examples, it is obvious that with the same luminous flux created, LED lamps consume the least electricity and are more economical than incandescent lamps. At the time of this writing (2013), the price of LED lamps is many times higher than the price of incandescent lamps. Despite this, some countries have banned or are about to ban the sale of incandescent lamps due to their high power.

The power of household electrical appliances may differ depending on the manufacturer, and is not always the same when the appliance is in operation. Below are the approximate capacities of some household appliances.



• Household air conditioners for cooling a residential building, split system: 20–40 kilowatts
• Monoblock window air conditioners: 1–2 kilowatts
• Ovens: 2.1–3.6 kilowatts
• Washing machines and dryers: 2–3.5 kilowatts
• Dishwashers: 1.8–2.3 kilowatts
• Electric kettles: 1–2 kilowatts
• Microwave ovens: 0.65–1.2 kilowatts
• Refrigerators: 0.25–1 kilowatt
• Toasters: 0.7–0.9 kilowatts

Power in sports

It is possible to evaluate work using power not only for machines, but also for people and animals. For example, the power with which a basketball player throws a ball is calculated by measuring the force she applies to the ball, the distance the ball has traveled, and the time that force has been applied. There are websites that allow you to calculate work and power during exercise. The user selects the type of exercise, enters the height, weight, duration of the exercise, after which the program calculates the power. For example, according to one of these calculators, the power of a person with a height of 170 centimeters and a weight of 70 kilograms, who did 50 push-ups in 10 minutes, is 39.5 watts. Athletes sometimes use devices to measure the amount of power a muscle is working during exercise. This information helps determine how effective their chosen exercise program is.

Dynamometers

To measure power use special devices- dynamometers. They can also measure torque and force. Dynamometers are used in various industries, from engineering to medicine. For example, they can be used to determine the power of a car engine. To measure the power of cars, several main types of dynamometers are used. In order to determine the engine power using dynamometers alone, it is necessary to remove the engine from the car and attach it to the dynamometer. In other dynamometers, the force for measurement is transmitted directly from the wheel of the car. In this case, the car's engine through the transmission drives the wheels, which, in turn, rotate the rollers of the dynamometer, which measures the power of the engine under various road conditions.

Dynamometers are also used in sports and medicine. The most common type of dynamometer for this purpose is isokinetic. Usually this is a sports simulator with sensors connected to a computer. These sensors measure the strength and power of the whole body or individual muscle groups. The dynamometer can be programmed to give signals and warnings if the power exceeds a certain value. This is especially important for people with injuries during the rehabilitation period, when it is necessary not to overload the body.

According to some provisions of the theory of sports, the greatest sports development occurs under a certain load, individual for each athlete. If the load is not heavy enough, the athlete gets used to it and does not develop his abilities. If, on the contrary, it is too heavy, then the results deteriorate due to overload of the body. Exercise stress during some exercise, such as cycling or swimming, depends on many factors environment such as road conditions or wind. Such a load is difficult to measure, but you can find out with what power the body counteracts this load, and then change the exercise scheme, depending on the desired load.

Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question to TCTerms and within a few minutes you will receive an answer.

Power is a physical indicator. It defines the work done over time and helps measure energy change. Thanks to the unit of measurement of current power, the high-speed energy flow of energy in any spatial interval is easily determined.

Calculation and types

Due to the direct dependence of power on the voltage in the network and the current load, it follows that this value can appear both from the interaction of a large current with a low voltage, and as a result of the occurrence of a significant voltage with a small current. This principle is applicable for transformation in transformers and for the transmission of electricity over long distances.

There is a formula for calculating this indicator. It has the form P = A / t = I * U, where:

• P is an indicator of current power, measured in watts;
• BUT - current work on the chain section, calculated in joules;
• t acts as the time interval during which the current work was performed, is determined in seconds;
• U is the voltage of the circuit section, calculated in Volts;
• I - current strength, calculated in amperes.

Electric power can have active and reactive indicators. In the first case, the power force is converted into another energy. It is measured in watts, as it contributes to the conversion of volts and amperes.

The reactive power indicator contributes to the occurrence of a self-inductive phenomenon. Such a transformation partially returns energy flows back to the network, due to which there is a shift of current values and voltages with a negative impact on the power grid.

Definition of active and reactive indicator

The active power force is calculated by determining general meaning single-phase circuit in a sinusoidal current for the desired time period. The calculation formula is presented as an expression P = U * I * cos φ, where:

• U and I act as the rms current value and voltage;
• cos φ is the angle of phase shift between these two quantities.

Thanks to the power activity, electricity is converted into other types of energy: thermal and electromagnetic energy. Any electrical network with a current of a sinusoidal or non-sinusoidal direction determines the activity of the circuit section by summing the powers of each individual circuit gap. The electrical power of a three-phase circuit section is determined by the sum of each phase power.

A similar indicator of the active power force is the value of the transmission power, which is calculated by the difference between its fall and reflection.

The reactive index is measured in volt-amperes. It is a value used to determine the electrical loads created by electromagnetic fields inside the AC circuit. The unit of measurement of electric current power is calculated by multiplying the rms value of the voltage in the network U by the alternating current I and the phase sine angle between these values. The calculation formula is as follows: Q = U * I * sin.

If the current load is less than the voltage, then the phase displacement is positive value if the opposite is negative.

Measurement value

The basic electrical unit is power. In order to determine what the power of an electric current is measured in, it is necessary to study the main characteristics of this quantity. According to the laws of physics, it is measured in watts. In production conditions and in everyday life, the value is translated into kilowatts. Large power scale calculations require conversion to megawatts. This approach is practiced at power plants to generate electrical energy. Work is measured in joules. The value is determined by the following relations:

Consumer power strength is indicated on the appliance itself or in the passport for it. By defining this parameter, you can get the values ​​​​of indicators such as voltage and electric current. The indicators used indicate what the electrical power is measured in, they can act as wattmeters and varmeters. The reactive power of the power indicator is determined by a phase meter, a voltmeter and an ammeter. The state standard of what the current power is measured in is the frequency range from 40 to 2500 Hz.

Calculation examples

To calculate the current of the kettle with an electric power of 2 kW, the formula I \u003d P / U \u003d (2 * 1000) / 220 \u003d 9 A is used. To power the device into the mains, the connector length of 6 A is not used. The above example is applicable only when the phase and current voltage. According to this formula, the indicator of all household appliances is calculated.

If the circuit is inductive or has a large capacitance, then it is necessary to calculate the power unit of the current using other approaches. For example, the power in an engine with alternating current is determined using the formula P = I * U * cos.

When connecting the device to a three-phase network, where the voltage will be 380 V, to determine the indicator, the powers of each phase are summed up separately.

As an example, consider a boiler of three phases with a power capacity of 3 kW, each of which consumes 1 kW. The phase current is calculated by the formula I \u003d P / U * cos φ \u003d (1 * 1000) / 220 \u003d 4.5 A.

On any device, an indicator of electrical power is indicated. The transmission of a large power volume, used in production, is carried out along lines with high voltage. Energy is converted by substations into electricity and supplied for use in the power grid.

Thanks to simple calculations, the power value is determined. Knowing its value, you can make the correct selection of voltage for full-fledged work household and industrial devices. This approach will help to avoid burnout of electrical appliances and protect the power grid from power surges.

Executed for a certain period of time, to this period of time.

Effective power, engine power given to the working machine directly or through a power transmission. Distinguish between useful, full and nominal E. m. of the engine. Useful is called the E. m. of the engine, minus the power consumption for actuating the auxiliary units or mechanisms necessary for its operation, but having a separate drive (not directly from the engine). Full E. m. - engine power without deducting the indicated costs. Rated E. m., or simply rated power, - E. m., guaranteed by the manufacturer for certain operating conditions. Depending on the type and purpose of the engine, electric meters are installed, regulated by standards or specifications(for example, the maximum power of a ship's reversible engine at a certain crankshaft speed in the case of reversing the vessel is the so-called reverse power, the maximum power of an aircraft engine with a minimum specific fuel consumption is the so-called cruising power, etc.). E. m. depends on the forcing (intensification) of the working process, the size and mechanical efficiency of the engine.

Units

Another common unit of measure for power is horsepower.

Relationships between units of power

Units	Tue	kW	MW	kgf m/s	erg/s	l. from.
1 watt	1	10 -3	10 -6	0,102	10 7	1.36 10 -3
1 kilowatt	10 3	1	10 -3	102	10 10	1,36
1 megawatt	10 6	10 3	1	102 10 3	10 13	1.36 10 3
1 kilogram-force meter per second	9,81	9.81 10 -3	9.81 10 -6	1	9.81 10 7	1.33 10 -2
1 erg per second	10 -7	10 -10	10 -13	1.02 10 -8	1	1.36 10 -10
1 horsepower	735,5	735.5 10 -3	735.5 10 -6	75	7.355 10 9	1

Power in mechanics

If a force acts on a moving body, then this force does work. The power in this case is equal to the scalar product of the force vector and the velocity vector with which the body moves:

M- moment, - angular velocity, - pi, n- rotational speed (rpm).

Electric power

Electric power- a physical quantity that characterizes the rate of transmission or conversion of electrical energy.

S - Apparent power, VA

P - Active power, W

Q - Reactive power, VAr

Power Meters

Notes

see also

Links

• The influence of the form of electric current on its action. Magazine "Radio", number 6, 1999

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