If you need to bring power units into one system, you will need our power conversion - online converter. And below you can read how power is measured.
Power is a physical quantity equal to the ratio of work performed over a certain period of time to this period of time.
How is power measured?
The units of power that are known to every schoolchild and are accepted in the international community are watts. Named in honor of the scientist J. Watt. They are designated by the Latin W or vt.
1 Watt is a unit of power that produces 1 joule of work per second. A watt is equal to the power of a current, the strength of which is 1 ampere, and the voltage is 1 volt. In technology, megawatts and kilowatts are usually used. 1 kilowatt is equal to 1000 watts.
Power is also measured in erg per second. 1 erg per second. Equal to 10 to the minus seventh power of watt. Accordingly, 1 watt is equal to 10 to the seventh power erg/sec.
And the unit of measurement of power is considered to be the non-system “horsepower”. It was put into circulation back in the eighteenth century and continues to be used in the automotive industry. It is designated as follows:
- L.S. (in Russian),
- HP (in English).
- PS (in German),
- CV (in French).
When converting power, remember that there is incredible confusion in the RuNet when converting horsepower to watts. In Russia, CIS countries and some other countries 1 hp. equals 735.5 watts. In England and America, 1 hp equals 745.7 watts.
Hello! To calculate a physical quantity called power, they use the formula where the physical quantity - work - is divided by the time during which this work was performed.
She looks like this:
P, W, N=A/t, (W=J/s).
Depending on the textbooks and sections of physics, power in the formula can be denoted by the letters P, W or N.
Most often, power is used in such branches of physics and science as mechanics, electrodynamics and electrical engineering. In each case, power has its own formula for calculation. It is also different for alternating and direct current. Wattmeters are used to measure power.
Now you know that power is measured in watts. In English, watt is watt, international designation is W, Russian abbreviation- Tue. This is important to remember because in all household appliances there is such a parameter.
Power is a scalar quantity, it is not a vector, unlike force, which can have a direction. In mechanics, the general form of the power formula can be written as follows:
P=F*s/t, where F=A*s,
From the formulas you can see how instead of A we substitute the force F multiplied by the path s. As a result, power in mechanics can be written as force multiplied by speed. For example, a car having a certain power is forced to reduce speed when driving uphill, since this requires more force.
The average human power is taken to be 70-80 W. The power of cars, airplanes, ships, rockets and industrial plants is often measured in horsepower. Horsepower was used long before watts were introduced. One horsepower is equal to 745.7 W. Moreover, in Russia it is accepted that l. With. equal to 735.5 W.
If you are suddenly asked by chance 20 years later in an interview among passers-by about power, and you remember that power is the ratio of work A performed per unit time t. If you can say so, pleasantly surprise the crowd. Indeed, in this definition, the main thing to remember is that the divisor here is work A, and the divider is time t. As a result, having work and time, and dividing the first by the second, we get the long-awaited power.
When choosing in stores, it is important to pay attention to the power of the device. The more powerful the kettle, the faster it will heat the water. The power of the air conditioner determines how large a space it can cool without putting extreme load on the engine. How more power electrical appliance, the more current it consumes, the more electricity it will consume, the higher the electricity bill will be.
In general, electrical power is determined by the formula:
where I is current, U is voltage
Sometimes it is even measured in volt-amperes, written as V*A. The total power is measured in volt-amperes, and to calculate the active power you need to multiply the total power by the coefficient of performance (efficiency) of the device, then we get the active power in watts.
Often, appliances such as an air conditioner, refrigerator, or iron operate cyclically, turning on and off from the thermostat, and their average power per total time The work may be small.
In alternating current circuits, in addition to the concept of instantaneous power, which coincides with general physical power, there are active, reactive and apparent powers. Full power equal to the sum of active and reactive powers.
To measure power, electronic devices are used - wattmeters. The unit of measurement, Watt, got its name in honor of the inventor of the improved steam engine, which revolutionized the power plants of the time. Thanks to this invention, the development of industrial society accelerated, trains, steamships, and factories appeared that used the power of the steam engine for movement and production of products.
We have all come across the concept of power many times. For example, different cars have different engine power. Also, electrical appliances can have different power levels, even if they have the same purpose.
Power is a physical quantity that characterizes the speed of work.
Respectively, mechanical power is a physical quantity that characterizes the speed of mechanical work:
That is, power is work per unit of time.
Power in the SI system is measured in watts: [ N] = [W].
1 W is 1 J of work done in 1 s.
There are other units of power measurement, such as horsepower:
It is in horsepower that the power of a car engine is most often measured.
Let's return to the formula for power: We know the formula by which work is calculated: 
Therefore we can rearrange the expression for power:
Then in the formula we form the ratio of the displacement modulus to the period of time. This is, as you know, the speed:
Just note that in the resulting formula we use the velocity module, since we divided not the movement itself, but its module by time. So, power is equal to the product of the force modulus, the velocity modulus and the cosine of the angle between their directions.
This is quite logical: say, the power of the piston can be increased by increasing the force of its action. By applying greater force, he will make more work at the same time, that is, it will increase power. But even if we leave the force constant and make the piston move faster, it will undoubtedly increase the work done per unit of time. Consequently, the power will increase.
Examples of problem solving.
Task 1. The motorcycle's power is 80 hp. Moving on horizontal section, the motorcyclist reaches a speed of 150 km/h. At the same time, the engine operates at 75% of its capacity. maximum power. Determine the frictional force acting on the motorcycle.
Task 2. The fighter, under the influence of a constant thrust force directed at an angle of 45° to the horizon, accelerates from 150 m/s to 570 m/s. At the same time, the vertical and horizontal speed of the fighter increases by same value at every moment of time. The mass of the fighter is 20 tons. If the fighter accelerates for one minute, then what is the power of its engine?
Hello! To calculate a physical quantity called power, they use the formula where the physical quantity - work - is divided by the time during which this work was performed.
She looks like this:
P, W, N=A/t, (W=J/s).
Depending on the textbooks and sections of physics, power in the formula can be denoted by the letters P, W or N.
Most often, power is used in such branches of physics and science as mechanics, electrodynamics and electrical engineering. In each case, power has its own formula for calculation. It is also different for alternating and direct current. Wattmeters are used to measure power.
Now you know that power is measured in watts. In English, watt is watt, the international designation is W, the Russian abbreviation is W. This is important to remember, because all household appliances have this parameter.
Power is a scalar quantity, it is not a vector, unlike force, which can have a direction. In mechanics, the general form of the power formula can be written as follows:
P=F*s/t, where F=A*s,
From the formulas you can see how instead of A we substitute the force F multiplied by the path s. As a result, power in mechanics can be written as force multiplied by speed. For example, a car having a certain power is forced to reduce speed when driving uphill, since this requires more force.
The average human power is taken to be 70-80 W. The power of cars, airplanes, ships, rockets and industrial plants is often measured in horsepower. Horsepower was used long before watts were introduced. One horsepower is equal to 745.7 W. Moreover, in Russia it is accepted that l. With. equal to 735.5 W.
If you are suddenly asked by chance 20 years later in an interview among passers-by about power, and you remember that power is the ratio of work A performed per unit time t. If you can say so, pleasantly surprise the crowd. Indeed, in this definition, the main thing to remember is that the divisor here is work A, and the divider is time t. As a result, having work and time, and dividing the first by the second, we get the long-awaited power.
When choosing in stores, it is important to pay attention to the power of the device. The more powerful the kettle, the faster it will heat the water. The power of the air conditioner determines how large a space it can cool without putting extreme load on the engine. The greater the power of an electrical appliance, the more current it consumes, the more electricity it will consume, and the higher the electricity bill will be.
In general, electrical power is determined by the formula:
where I is current, U is voltage
Sometimes it is even measured in volt-amperes, written as V*A. The total power is measured in volt-amperes, and to calculate the active power you need to multiply the total power by the coefficient of performance (efficiency) of the device, then we get the active power in watts.
Often, appliances such as an air conditioner, refrigerator, or iron operate cyclically, turning on and off from the thermostat, and their average power over the total operating time can be small.
In alternating current circuits, in addition to the concept of instantaneous power, which coincides with general physical power, there are active, reactive and apparent powers. Apparent power is equal to the sum of active and reactive power.
To measure power, electronic devices are used - wattmeters. The unit of measurement, Watt, got its name in honor of the inventor of the improved steam engine, which revolutionized the power plants of the time. Thanks to this invention, the development of industrial society accelerated, trains, steamships, and factories appeared that used the power of the steam engine for movement and production of products.
We have all come across the concept of power many times. For example, different cars have different engine power. Also, electrical appliances can have different power levels, even if they have the same purpose.
Power is a physical quantity characterizing the speed of work.
Respectively, mechanical power is a physical quantity characterizing the speed of mechanical work:
That is, power is work per unit of time.
Power in the SI system is measured in watts: [ N] = [W].
1 W is 1 J of work done in 1 s.
There are other units of power measurement, such as horsepower:
It is in horsepower that the power of a car engine is most often measured.
Let's return to the formula for power: We know the formula by which work is calculated: 
Therefore we can rearrange the expression for power:
Then in the formula we form the ratio of the displacement modulus to the period of time. This is, as you know, the speed:
Just note that in the resulting formula we use the velocity module, since we divided not the movement itself, but its module by time. So, power is equal to the product of the force modulus, the velocity modulus and the cosine of the angle between their directions.
This is quite logical: say, the power of the piston can be increased by increasing the force of its action. By applying more force, it will do more work in the same time, that is, it will increase power. But even if we leave the force constant and make the piston move faster, it will undoubtedly increase the work done per unit of time. Consequently, the power will increase.
Examples of problem solving.
Task 1. The motorcycle's power is 80 hp. Moving along a horizontal section, a motorcyclist reaches a speed of 150 km/h. At the same time, the engine operates at 75% of its maximum power. Determine the frictional force acting on the motorcycle.
Task 2. The fighter, under the influence of a constant thrust force directed at an angle of 45° to the horizon, accelerates from 150 m/s to 570 m/s. At the same time, the vertical and horizontal speed of the fighter increases by the same amount at each moment of time. The mass of the fighter is 20 tons. If the fighter accelerates for one minute, then what is the power of its engine?
If you need to bring power units into one system, you will need our power conversion - online converter. And below you can read how power is measured.
Based on the operation of a residential electricity meter, it can be seen that the increase in kilowatt-hours occurs the faster the greater the load is supplied to the network. This is one of the ways power is measured. There are several varieties of the indicator, designated by the first letter of the English watt - W. The amount of energy consumption depends on the parameters of the electrical circuit of the home - it is directly proportional to the power of the connected current collectors.
Types of electrical power
The physical quantity W represents the rate of change, transmission, consumption and conversion of energy of the system under consideration. Specifically, the definition of power sounds like the ratio of the work performed during a certain period to the period of time of action: W = ΔA/Δ t, J/s = watt (W).
In a relationship electrical network We are talking about the movement of a charge under the influence of voltage: A = U. The potential between two points of a conductor is an indicator of the energy of motion of a single nucleon. Full work flow of the total number of electrons - Аn=U*Q, where Q - total number charges in the network. In this case, the power formula takes the form W=U*Q/t, the expression Q/t is electric current (I), that is, W=U*I.
In energy there are several terms W:
The nature of the installed equipment determines the redundancy of Wр, when capacitive devices predominate and the potential increases, or deficiency, if the inductance of the network prevails (the voltage decreases). Using the principle of opposite action, devices have been developed that make it possible to compensate for the harmfulness of Wр and improve the quality and efficiency of energy supply.
Impact of network parameters per kilowatt
From the formula W=U*I, it is clear that power depends simultaneously on two characteristics of the power system - voltage and current. Their influence on network parameters is equal. Education process electrical power can be described as follows:
- U is the work spent on moving 1 coulomb;
- I is the number of charges flowing through the conductor in 1 second.
Based on the calculated value of W, the consumed network energy is determined by multiplying the amount of power by the time it is consumed. By changing one of the parameters W towards decreasing or increasing, you can keep the energy of the system at a constant level - get high strength current at low voltage or high network potential with weak coulomb movement.
Converter devices designed to change parameters, called voltage or current transformers. They are installed at step-up or step-down electrical substations to transfer energy from a source to consumers over long distances.
Load measurement methods
You can find out the power of the device by referring to its instructions or passport, and if not, look at the nameplate attached to the body. If manufacturer data is not available, then other methods are available to determine the energy efficiency of the equipment. The main one is measure the load using a wattmeter(device for recording electrical power).
According to their purpose, they are divided into 3 classes: direct current and low frequency (LF), optical and high impulse. The latter belong to the radio range and are divided into 2 types: those included in the line break (passing power) and those mounted at the end point of the route as a matched (absorbed) load. According to the method of conveying information to the operator, a distinction is made between digital and analogue devices - pointer-type and recorder-type devices. Brief characteristics some meters:
In addition to the help of special devices, power is determined by applying a calculation formula: an ammeter is connected to the break in one of the supply wires, the current and voltage of the network are determined. Multiplying the quantities will give the desired result.
Electric power- a physical quantity characterizing the speed of transmission or conversion of electrical energy.
Encyclopedic YouTube
1 / 5
✪ Lesson 363. Power in a circuit alternating current
✪ Active, reactive and apparent power. What is it, using a visual analogy as an example.
✪ Work and power electric current. Current work | Physics 8th grade #19 | Info lesson
✪ What is the difference between VOLTAGE and CURRENT
✪ Watt Joule and Horsepower
Subtitles
Instantaneous electrical power
Instantaneous power is the product of the instantaneous values of voltage and current in any part of the electrical circuit.
DC power
Since the current and voltage values are constant and equal to the instantaneous values at any time, the power can be calculated using the formula:
P = I ⋅ U (\displaystyle P=I\cdot U) .For a passive linear circuit in which Ohm's law is observed, we can write:
P = I 2 ⋅ R = U 2 R (\displaystyle P=I^(2)\cdot R=(\frac (U^(2))(R))), Where R (\displaystyle R)- electrical resistance .If the circuit contains an EMF source, then the electrical power given off or absorbed by it is equal to:
P = I ⋅ E (\displaystyle P=I\cdot (\mathcal (E))), Where E (\displaystyle (\mathcal (E)))- EMF.If the current inside the EMF is opposite to the potential gradient (flows inside the EMF from plus to minus), then the power is absorbed by the source of the EMF from the network (for example, when an electric motor is running or charging a battery), if it is codirectional (flows inside the EMF from minus to plus), then it is given off by the source into the network (say, when operating a galvanic battery or generator). When taking into account the internal resistance of the EMF source, the power released on it p = I 2 ⋅ r (\displaystyle p=I^(2)\cdot r) added to what is absorbed or subtracted from what is given.
AC power
In AC circuits, the formula for DC power can only be used to calculate instantaneous power, which varies greatly over time and for most simple practical calculations not very useful directly. Direct calculation of average power requires integration over time. To calculate power in circuits where voltage and current vary periodically, average power can be calculated by integrating the instantaneous power over the period. On practice highest value has a power calculation in circuits of alternating sinusoidal voltage and current.
In order to connect the concepts of total, active, reactive power and power factor, it is convenient to turn to the theory of complex numbers. We can assume that the power in an alternating current circuit is expressed by a complex number such that active power is its real part, reactive power is its imaginary part, total power is its module, and the angle (phase shift) is its argument. For such a model, all the relations written below turn out to be valid.
Active power
.
Reactive power is a quantity characterizing the loads created in electrical devices by energy fluctuations electromagnetic field in a sinusoidal alternating current circuit, equal to the product of the rms voltage values U (\displaystyle U) and current I (\displaystyle I), multiplied by the sine of the phase angle φ (\displaystyle \varphi ) between them: Q = U ⋅ I ⋅ sin φ (\displaystyle Q=U\cdot I\cdot \sin \varphi )(if the current lags behind the voltage, the phase shift is considered positive, if it leads, it is considered negative). Reactive power is related to apparent power S (\displaystyle S) and active power P (\displaystyle P) ratio: |.
Q |
= S 2 − P 2 (\displaystyle |Q|=(\sqrt (S^(2)-P^(2)))) φ (\displaystyle \varphi ) The physical meaning of reactive power is energy pumped from the source to the reactive elements of the receiver (inductors, capacitors, motor windings), and then returned by these elements back to the source during one oscillation period, referred to this period. It should be noted that the value for the values 0 to plus 90° is a positive value. Magnitude φ (\displaystyle \varphi ) sin φ (\displaystyle \sin \varphi ) for values 0 to −90° is a negative value. According to the formula
Q = U I sin φ (\displaystyle Q=UI\sin \varphi ) , reactive power can be either a positive value (if the load is active-inductive in nature) or negative (if the load is active-capacitive in nature). This circumstance emphasizes the fact that reactive power does not participate in the operation of electric current. When a device has positive reactive power, it is customary to say that it consumes it, and when it produces negative power, it produces it, but this is purely a convention due to the fact that most power-consuming devices (for example, asynchronous motors), as well as purely active loads connected through a transformer, are active-inductive. Synchronous generators installed in power plants can both produce and consume reactive power depending on the magnitude of the excitation current flowing in the generator rotor winding. Due to this feature of synchronous electric machines the specified network voltage level is regulated. To eliminate overloads and improve power factor
electrical installations
reactive power is compensated.
The unit of total electrical power is volt-ampere (Russian designation: VA; international: V·A) .
Total power is a value equal to the product of the effective values of the periodic electric current I (\displaystyle I) in circuit and voltage U (\displaystyle U) on its clamps: S = U ⋅ I (\displaystyle S=U\cdot I); is related to active and reactive powers by the ratio: S = P 2 + Q 2 , (\displaystyle S=(\sqrt (P^(2)+Q^(2))),) Where P (\displaystyle P)- active power, Q (\displaystyle Q)- reactive power (with inductive load Q > 0 (\displaystyle Q>0), and with capacitive Q< 0 {\displaystyle Q<0} ).
The vector relationship between total, active and reactive power is expressed by the formula: S⟶ = P⟶ + Q⟶.(\displaystyle (\stackrel (\longrightarrow )(S))=(\stackrel (\longrightarrow )(P))+(\stackrel (\longrightarrow )(Q)).)
Complex power
Power, similar to impedance, can be written in complex form: Where S ˙ = U ˙ I ˙ ∗ = I 2 Z = U 2 Z ∗ , (\displaystyle (\dot (S))=(\dot (U))(\dot (I))^(*)=I^ (2)\mathbb (Z) =(\frac (U^(2))(\mathbb (Z) ^(*))),) U ˙ (\displaystyle (\dot (U))) - complex stress, I ˙ (\displaystyle (\dot (I))) - complex current, Z (\displaystyle \mathbb (Z) )- impedance, * - complex conjugation operator. Complex power module| S (\displaystyle S) S˙ | (\displaystyle \left|(\dot (S))\right|) equal to full power P (\displaystyle P). Real part R e (S ˙) (\displaystyle \mathrm (Re) ((\dot (S)))) equal to active power Q (\displaystyle Q), and imaginary I m (S ˙) (\displaystyle \mathrm (Im) ((\dot (S))))
- reactive power
| with the correct sign depending on the nature of the load. | Power of some electrical appliances |
|---|---|
| The table shows the power values of some electrical consumers: | 1 |
| Electrical appliance | 10…20 |
| Power, W | 100…1700 |
| flashlight bulb | 200…1500 |
| network router, hub | 15…200 |
| PC system unit | 2…40 |
| server system unit | 5…30 |
| PC monitor CRT | 25…150 |
| LCD PC monitor | 15…700 |
| household fluorescent lamp | 100… 3000 |
| household incandescent lamp | 300…2 000 |
| Household refrigerator | 350…2 000 |
| Electric vacuum cleaner | 1 000…2 000 |
| Electric iron | 1 000…5 500 |
| Washing machine | 45 000…50 000 |
| Electric stove | 650 000 |
| Household welding machine | 1 000 000...5 000 000 |
| Tram engine | 6 000 000…9 000 000 |
Electric locomotive engine
Electric motor of a mine hoisting machine
Rolling mill electric motors
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 in the 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:
- washing machine power 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 connect it to an electric meter and turn it on, then exactly an 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, an 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.