What is power equal to in physics? Units of power measurement and types of engine power
Power is physical indicator. It defines the work done over a period of 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 low current. This principle is applicable for transformation in transformers and for transmitting electricity over vast 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;
- A - current work on the chain section, calculated in joules;
- t is the time interval during which the current work was performed, determined in seconds;
- U is the electrical voltage of the circuit section, calculated in Volts;
- I - current strength, calculated in amperes.
Electrical power can have active and reactive indicators. In the first case, the transformation of power force into other energy occurs. It is measured in watts because it contributes to the conversion of volts and amperes.
The reactive power indicator contributes to the occurrence of self-inductive phenomenon. This conversion partially returns energy flows back to the network, causing current values shift and voltages with a negative impact on the power grid.
Definition of active and reactive indicator
The active power force is calculated by determining the total value of a single-phase circuit in a sinusoidal current for the desired time period. The calculation formula is presented as the expression P = U * I * cos φ, where:
- U and I act as rms current and voltage;
- cos φ is the interfacial shift angle between these two quantities.
Thanks to power activity, electricity is converted into other energy types: thermal and electromagnetic energy. Any electrical network with a current of sinusoidal or non-sinusoidal direction determines the activity of the circuit section by summing the powers of each individual circuit section. The electrical power of a three-phase circuit section is determined by the sum of each phase power.
A similar indicator of active power force is the magnitude of transmission power, which is calculated by the difference between its incidence and reflection.
The reactive indicator is measured in volt-amperes. It is a quantity used to determine the electrical loads created by electromagnetic fields within an alternating current circuit. Power unit electric current 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; if, on the contrary, it is negative.
Measurement value
The basic electrical unit is power. In order to determine how the power of an electric current is measured, 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 converted into kilowatts. Calculations of large power scales require conversion to megawatts. This approach is practiced at power plants to produce electrical energy. Work is calculated in joules. The value is determined by the following relationships:
The power consumption is indicated on the electrical appliance itself or in its passport. By determining this parameter, you can obtain the values of indicators such as voltage and electric current. The indicators used indicate how electrical power is measured; they can be in the form of wattmeters and varmeters. The reactive power of the power indicator is determined by a phase meter, voltmeter and ammeter. The state standard for how current power is measured is the frequency range from 40 to 2500 Hz.
Calculation examples
To calculate the kettle current with an electrical power of 2 kW, use the formula I = P / U = (2 * 1000) / 220 = 9 A. 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 line is completely identical and current voltage. This formula is used to calculate the indicator of all household appliances.
If the circuit is inductive or has a large capacitance, then it is necessary to calculate the power unit of current using other approaches. For example, power in an AC motor 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, the power of each phase separately is summed up to determine the indicator.
As an example, we can consider a boiler with three phases with a power capacity of 3 kW, each of which consumes 1 kW. The phase current is calculated by the formula I = P / U * cos φ = (1 * 1000) / 220 = 4.5 A.
On any device the electrical power indicator is indicated. Large power transmission used in production is carried out via high voltage lines. Energy is converted using substations into electric current and is supplied for use in the electrical network.
Thanks to simple calculations, the power value is determined. Knowing its value, you can make the correct selection of voltage for the full operation of household and industrial devices. This approach will help avoid burnout of electrical appliances and protect electrical networks from voltage surges.
Back in the 18th century, power began to be measured in horsepower. Until now, this physical quantity is used to indicate the power of engines. Next to the power indicator of the internal combustion engine in watts, they continue to write the value in hp.
Power as a physical quantity, power formula
A value that shows how quickly energy is converted, transmitted, or consumed in a system—power. It is important to characterize the energy conditions how quickly the process is performed. The work performed per unit of time is called power:
- A – work;
- t – time.
Mechanical power and electrical power can be taken into account separately.
To get an answer to the question: how is mechanical power measured, consider the effect of force on a moving body. Force does work, power in this case is determined by the formula:
- F – force;
- v – speed.
During rotational motion, this value is determined taking into account the moment of force and rotational speed, “rpm.”
Relationship between electric current and power
In electrical engineering, the work will be U - the voltage that moves 1 coulomb, the number of coulombs moved per unit time is the current (I). Electric current power or electrical power P is obtained by multiplying the current by the voltage:
This is a complete job done in 1 second. The dependence here is direct. By changing the current or voltage, the power consumed by the device is changed.
The same P value is achieved by varying one of two values.
Definition of current power unit
The unit for measuring current power is named after James Watt, a Scottish mechanical engineer. 1 W is the power generated by a current of 1 A at a potential difference of 1 V.
For example, a source with a voltage of 3.5 V creates a current of 0.2 A in the circuit, then the current power will be:
P = U*I = 3.5*0.2 = 0.7 W.
Attention! In mechanics, power is usually represented by the letter N, in electrical engineering - by the letter P. How are n and P measured? Regardless of the designation, it is one quantity, and it is measured in watts "W".
Watt and other power units
When talking about how power is measured, you need to know what we are talking about. Watt is a value corresponding to 1 J/s. It is adopted in the International System of Units. In what other units is power measured? The branch of science astrophysics works with a unit called erg/s. Erg is a very small value, equal to 10-7 W.
Another, still common, unit from this series is “horsepower”. In 1789, James Watt calculated that a 75 kg load could be pulled from a shaft by one horse at a speed of 1 m/s. Based on the calculation of such labor intensity, the engine power can be measured by this value in the ratio:
1 hp = 0.74 kW.
Interesting. Americans and British believe that 1 hp. = 745.7 W, and Russians – 735.5 W. There is no point in arguing who is right and who is wrong, since this is an extra-systemic measure and should not be used. The International Organization of Legal Metrology recommends its withdrawal from circulation.
In Russia, when calculating a CASCO or OSAGO policy, these data from the car’s power unit are used.
Formula for the relationship between power, voltage and current
In electrical engineering, work is considered as a certain amount of energy supplied by a power source to the operation of an electrical appliance over a period of time. Therefore, electrical power is a quantity that describes the speed of transformation or transmission of electricity. Her formula for DC looks like this:
- U – voltage, V;
- I – current strength, A.
For some cases, using the Ohm's law formula, power can be calculated by substituting the resistance value:
P = I*2*R, Where:
- I – current strength, A;
- R – resistance, Ohm.
When calculating the power of AC circuits, you will have to deal with three types:
- its active formula: P = U*I*cos ϕ, where is the phase shift angle coefficient;
- reactive is calculated: Q = U*I*sin ϕ ;
- the complete one is presented in the form: S = √P2 + Q2, where P is active and Q2 is reactive.
Calculations for single-phase and three-phase AC circuits are performed using different formulas.
Important! Consumers of electricity in enterprises are mostly asynchronous motors, transformers and other inductive receivers. During operation, they use reactive power, which, flowing through power lines, leads to additional load on power lines. To improve energy quality, reactive energy compensation is used in the form of capacitor units.
Instruments for measuring electrical power
A wattmeter allows you to measure power. It has two windings. One is connected to the circuit in series, like an ammeter, the second in parallel, like a voltmeter. In electrical power installations, wattmeters measure values in kilowatt-hour “kW*h.” Measurements require not only electrical energy, but also laser energy. Devices capable of measuring this indicator are manufactured in both stationary and portable versions. With their help, the level of laser radiation from equipment using this type of energy is assessed. One of the portable meters is LP1, made by a Japanese manufacturer. LP1 allows you to directly determine the intensity of light radiation, for example, in the visual spot of optical devices of DVD players.
Power in household electrical appliances
To heat the metal filament of a light bulb, increase the temperature of the working surface of an iron or other household appliance, a certain amount of electricity is spent. Its value, taken by the load per hour, is considered the power consumption of this device.
Attention! If the light bulb says “40 W, 230 V,” this means that in 1 hour it consumes 40 W from the AC network. Knowing the number of light bulbs and parameters, they calculate how much energy is spent on lighting rooms per month.
How to convert watts
Since watt– the value is small, in everyday life they operate in kilowatts, they use a system for converting quantities:
- 1 W = 0.001 kW;
- 10 W = 0.01 kW;
- 100 W = 0.1 kW;
- 1000 W = 1 kW.
Power of some electrical appliances, W
Average electricity consumption values for household devices:
- stoves – 110006000 W;
- refrigerators – 150-600 W;
- washing machines – 1000-3000 W;
- vacuum cleaners – 1300-4000 W;
- electric kettles - 2000-3000 W.
The parameters of each household appliance are indicated in the passport and are also indicated on the body. The exact values for consumer information are defined there.
Video
Performed over a certain period of time, to this period of time.
Effective power, engine power supplied to the working machine directly or through a power transmission. There are useful, total, and nominal E.M. of the engine. The useful energy is the electric power of an engine minus the power consumption for actuating auxiliary units or mechanisms necessary for its operation, but having a separate drive (not directly from the engine). Total E.m. is the engine power without deducting the specified costs. Rated E.M., or simply rated power, is E.M. guaranteed by the manufacturer for certain operating conditions. Depending on the type and purpose of the engine, electric motors are installed, regulated by standards or technical specifications (for example, the maximum power of a marine reversible engine at a certain crankshaft rotation speed in the case of a vessel reversing - the so-called reverse power, the maximum power of an aircraft engine at a minimum specific fuel consumption - the so-called cruising power, etc.). E.m. depends on the acceleration (intensification) of the working process, the size and mechanical efficiency of the engine.
Units of measurement
Another common unit of measurement for power is horsepower.
| Units | W | kW | MW | kgf m/s | erg/s | l. With. |
|---|---|---|---|---|---|---|
| 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 |
Mechanical power
If a force acts on a moving body, then this force does work. 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, - number pi, n- rotation speed (rpm).
Electrical power
Electrical power- a physical quantity characterizing the speed of transmission or conversion of electrical energy.
S - Apparent power, VA
P - Active power, W
Q - Reactive power, VAR
Power measuring instruments
Notes
See also
Links
- The influence of the shape of electric current on its action. Radio magazine, number 6, 1999
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See what “Power (physics)” is in other dictionaries:
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that is, the product of force vectors and speed of movement is power. How is it measured? According to the international SI system, the unit of measurement for this quantity is 1 Watt.
Watt and other power units
Watt means power, where one joule of work is done in one second. The last unit was named after the Englishman J. Watt, who invented and built the first steam engine. But he used another quantity - horsepower, which is still used today. One horsepower is approximately equal to 735.5 watts.
Thus, in addition to Watts, power is measured in metric horsepower. And for a very small value, Erg is also used, equal to ten to the minus seventh power of Watt. It is also possible to measure in one unit of mass/force/meters per second, which is equal to 9.81 Watts.
Engine power
This value is one of the most important in any motor, which comes in a wide range of power. For example, an electric razor has hundredths of a kilowatt, and a spaceship rocket has millions.
Different loads require different power to maintain a certain speed. For example, a car will become heavier if more cargo is placed in it. Then the friction force on the road will increase. Therefore, to maintain the same speed as in an unloaded state, more power will be required. Accordingly, the engine will consume more fuel. All drivers know this fact.
But at high speeds, the inertia of the machine is also important, which is directly proportional to its mass. Experienced drivers who are aware of this fact find the best combination of fuel and speed when driving so that less gasoline is consumed.
Current power
How is current power measured? In the same SI unit. It can be measured by direct or indirect methods.
The first method is implemented using a wattmeter, which consumes significant energy and heavily loads the current source. It can be used to measure ten watts or more. The indirect method is used when it is necessary to measure small values. The instruments for this are an ammeter and a voltmeter connected to the consumer. The formula in this case will look like this:
With a known load resistance, we measure the current flowing through it and find the power as follows:
P = I 2 ∙ R n.
Using the formula P = I 2 /R n, the current power can also be calculated.
How it is measured in a three-phase current network is also no secret. For this, an already familiar device is used - a wattmeter. Moreover, the problem of how electrical power is measured can be solved using one, two or even three devices. For example, a four-wire installation would require three devices. And for a three-wire with an asymmetric load - two.
What is strength and power? How this indicator is measured, what instruments are used, and how these are used in practice, we will consider later in the article.
Strength
In the world, all bodies of physical nature begin to move due to force. When exposed to it, with the same or opposite direction of movement of the body, work is done. Thus, some force acts on the body.
Thus, a bicycle moves off thanks to the strength of a person’s legs, and the train is affected by the traction force of an electric locomotive. A similar impact occurs with any movement. The work of a force is the quantity in which the modulus of the force, the modulus of displacement of the point of its application, and the cosine of the angle between the vectors of these indicators are multiplied. The formula in this case looks like this:
A = F s cos (F, s)
If the angle between these vectors is not zero, then work is always done. Moreover, it can have both positive and negative meaning. There will be no force acting on the body at an angle of 90°.
Consider, for example, a cart pulled by the muscular power of a horse. In other words, the work is done by the traction force in the direction of movement of the cart. But when directed downwards or perpendicularly, it does no work (by the way, horsepower is what engine power is measured in).
The work done by a force is a scalar quantity and is measured in joules. It could be:
- resultant (under the influence of several forces);
- non-constant (then the calculation is performed with an integral).
Power
How is this quantity measured? First, let's look at what it is. It is clear that the body begins to move due to the force exerted. However, in practice, in addition to this, it is necessary to know exactly how it is accomplished.
The work may be completed within different time frames. For example, the same action can be performed by a small motor or a large electric motor. The only question is how long it will take to produce it. The quantity responsible for this task is power. How it is measured becomes clear from the definition - this is the ratio of work for a specific time to its value:
By logical steps we arrive at the following formula:
that is, the product of force vectors and speed of movement is power. How is it measured? According to the international SI system, the unit of measurement for this quantity is 1 Watt.
Watt and other power units
Watt means power, where one joule of work is done in one second. The last unit was named after the Englishman J. Watt, who invented and built the first steam engine. But he used another quantity - horsepower, which is still used today. approximately equal to 735.5 watts.
Thus, in addition to Watts, power is measured in metric horsepower. And for a very small value, Erg is also used, equal to ten to the minus seventh power of Watt. It is also possible to measure in one unit of mass/force/meters per second, which is equal to 9.81 Watts.
Engine power
This value is one of the most important in any motor, which comes in a wide range of power. For example, an electric razor has hundredths of a kilowatt, and a spaceship rocket has millions.
Different loads require different power to maintain a certain speed. For example, a car will become heavier if more cargo is placed in it. Then the road will increase. Therefore, to maintain the same speed as in an unloaded state, more power will be required. Accordingly, the engine will consume more fuel. All drivers know this fact.
But at high speeds, the inertia of the machine is also important, which is directly proportional to its mass. Experienced drivers who are aware of this fact find the best combination of fuel and speed when driving so that less gasoline is consumed.
Current power
How is current power measured? In the same SI unit. It can be measured by direct or indirect methods.
The first method is implemented using a wattmeter, which consumes significant energy and heavily loads the current source. It can be used to measure ten watts or more. The indirect method is used when it is necessary to measure small values. The instruments for this are an ammeter and a voltmeter connected to the consumer. The formula in this case will look like this:
With a known load resistance, we measure the current flowing through it and find the power as follows:
P = I 2 ∙ R n.
Using the formula P = I 2 /R n, the current power can also be calculated.
How it is measured in a three-phase current network is also no secret. For this, an already familiar device is used - a wattmeter. Moreover, it is possible to solve the problem of what is measured using one, two or even three instruments. For example, a four-wire installation would require three devices. And for a three-wire with an asymmetric load - two.
