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What Is The Definition Of Power In Physics

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What is Power in Physics?

Considering the definition of power and the two ways to find it yields multiple ways to increase something’s power: increase its strength or get the same work done faster . A powerful car is strong and fast, and a weak one is neither. The more easily and quickly work can be done, the more powerful the entity doing the work.


  • How to increase power: Get more done in a shorter time period.

This also implies that a very strong machine, say a highly muscular bodybuilder, could still lack power. A person that can lift a very heavy load, but only very slowly, is less powerful than someone who can lift it fast.

Similarly, a very fast machine or person that doesn’t get much done, someone rapidly flailing in place but getting nowhere, is not actually powerful.

Work Energy And Power

Work, Energy and Power are fundamental concepts of Physics. Work is the displacement of an object when a force is applied to it. We define the capacity to do the work as energy. Power is the work done per unit of time. This article discusses work, energy and power in detail.

Despite The Diagonal Motion Along The Staircase It Is Often Assumed That The Horizontal Motion Is Constant And All The Force From The Steps Is Used To Elevate The Student Upward At A Constant Speed

Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. When a force is applied to move an object, work is done on the object. Power that may be translated into motion, overcoming resistance or causing a physical change

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Definition Of Power From Electricity And From Energy

In the electricity topic, my physics book has defined Power as $P=IV$, $I$ being current and $V$ as voltage.

But then later in the Energy topic, power has been defined as $P=\frac=\frac$. The book also states that it is the same power we are talking about in both sections.

Therefore $IV=\frac$, But I don’t see the logical link in this last equation. I think the definition from Electricity is a specific form of the definition from Energy.

Take $IV=\frac\int\vec\cdot d\vec=\fracdq\left=\frac$. You can think of it as the time rate of change of the work done by the electric field on a test charge, if you like.

Electrical Definition

Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter $P$. The term wattage is used colloquially to mean “electric power in watts.” The electric power in watts produced by an electric current $I$ consisting of a charge of $Q$ coulombs every $t$ seconds passing through an electric potential difference of $V$ is


Energy Definition

Power, as a function of time, is the rate at which work is done, . so it can be expressed by this equation:


Because work is a force applied over a distance, this can be rewritten as:

$}=}\cdot }}}}$

And with distance per unit time being a velocity, power can likewise be understood as:

$}\cdot }}$

Knowing from Newton’s 2nd Law that force is mass times acceleration, the expression for power can also be written as:

$}\cdot }}$

$}\cdot }}}}$


Average Electrical Power For Sinusoidal Voltages

Power in Physics and Electricity

The average power consumed by a two-terminal electrical device is a function of the root mean square values of the sinusoidalvoltage across the terminals and the sinusoidal current passing through the device. That is,


P is the average power, measured in watts
I is the root mean square value of the sinusoidal alternating current , measured in amperes
V is the root mean square value of the sinusoidal alternating voltage, measured in volts
is the phase angle between the voltage and the current sine functions.

The amplitudes of sinusoidal voltages and currents, such as those used almost universally in mains electrical supplies, are normally specified in terms of root mean square values. This makes the above calculation a simple matter of multiplying the two stated numbers together.

This figure can also be called the effective power, as compared to the larger apparent power which is expressed in volt-amperes reactive and does not include the cos term due to the current and voltage being out of phase. For simple domestic appliances or a purely resistive network, the cos term can often be assumed to be unity, and can therefore be omitted from the equation. In this case, the effective and apparent power are assumed to be equal.

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An Analogy With Containers Of Water

Figure 2 shows a mug with a small amount of water being poured quickly and a jug holding a greater amount of water being poured more slowly. The mug is delivering more water in a given amount of time, but the total amount of water delivered will be less than the jug. The analogy is that the mug has higher power, but lower energy. The jug releases smaller amounts of liquid for a longer period of time. The analogy continues with the jug having a smaller power output but more energy. The mug releases all its water very quickly. Conversely, the jug holds much more water , even if it is not losing it quickly.

Is Power A Scalar Quantity

Power is a scalar quantity because it is a ratio of two scalar quantities.

Watch this fun and engaging rapid fire session based on the topic Work, Energy and Power!

Work, Power and Energy is one of the important topics of JEE Main and JEE Advanced, watch the video and understand the type of questions asked from this topic!

Stay tuned to BYJUS and Fall in Love with Learning!

Put your understanding of this concept to test by answering a few MCQs. Click Start Quiz to begin!

Select the correct answer and click on the Finish buttonCheck your score and answers at the end of the quiz

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Conventions In The Electric Power Industry

In the , megawatt electrical refers by convention to the produced by a generator, while megawatt thermal or thermal megawatt refers to produced by the plant. For example, the in Argentina uses a to generate 2109 MWt , which creates steam to drive a turbine, which generates 648 MWe . Other are sometimes used, for example gigawatt electrical . The , which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol and so these units are non-SI. In compliance with SI, the energy company uses the unit megawatt for produced electrical power and the equivalent unit per second for delivered heating power in a station such as .

When describing electricity, another distinction is made between the watt and the . While these units are equivalent for simple , they differ when loads exhibit .

usually report the power of their in units of watts, referring to the . This refers to the power that a would need to radiate to match the intensity of the transmitter’s .

Origin And Adoption As An Si Unit

Physics Definition of Power

The watt is named after the Scottish inventor . The unit name was proposed initially by in August 1882 in his President’s Address to the Fifty-Second Congress of the . Noting that units in the were named after leading physicists, Siemens proposed that watt might be an appropriate name for a unit of power. Siemens defined the unit consistently within the then-existing system of practical units as “the power conveyed by a current of an through the difference of potential of a Volt”.

In October 1908, at the International Conference on Electric Units and Standards in London, so-called “international” definitions were established for practical electrical units. Siemens’ definition was adopted as the “international” watt. The watt was defined as equal to 107 units of power in the “practical system” of units. The were dominant from 1909 until 1948. After the 9th in 1948, the “international” watt was redefined from practical units to absolute units . Concretely, this meant that 1 watt was now defined as the quantity of energy transferred in a unit of time, namely 1 J/s. In this new definition, 1 “absolute” watt = 1.00019 “international” watts. Texts written before 1948 are likely to be using the “international” watt, which implies caution when comparing numerical values from this period with the post-1948 watt. In 1960, the 11th General Conference on Weights and Measures adopted the “absolute” watt into the as the unit of power.

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Physics Definition Of Power

Physics Definition Of Power. Electric power = p = w/t = 18000 joule/120 seconds = 150 watt. It is the sum total of potential energy and kinetic energy which is the energy associated with the motion & position of any object.

A common physics lab involves quickly climbing a flight of stairs and using mass, height and time information to determine a student’s personal power. Energy the ability to do work. Power is energy per unit time.


Here in this article, you will learn about the definition of electric power. Despite the diagonal motion along the staircase, it is often assumed that the horizontal motion is constant and all the force from the steps is used to elevate the student upward at a constant speed.


It may be thermal , electrical, mechanical, chemical, radiant, or kinetic. Work is the energy needed to apply a force to move an object a particular distance, where force is parallel to the displacement.


Power is the rate at which that work is done. In physics, mechanical energy is the energy associated with the motion and position of an object usually in some force field (e.g.


Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. Power is the rate of doing work.

Source: philschatz.comSource:

History Of The Calendar

Artifacts from the suggest that the moon was used to reckon time as early as 6,000 years ago. were among the first to appear, with years of either 12 or 13 . Without to add days or months to some years, quickly drift in a calendar based solely on twelve lunar months. have a thirteenth month added to some years to make up for the difference between a full year and a year of just twelve lunar months. The numbers twelve and thirteen came to feature prominently in many cultures, at least partly due to this relationship of months to years. Other early forms of calendars originated in Mesoamerica, particularly in ancient Mayan civilization. These calendars were religiously and astronomically based, with 18 months in a year and 20 days in a month, plus five days at the end of the year.

The reforms of in 45 BC put the on a . This was faulty in that its intercalation still allowed the astronomical and to advance against it by about 11 minutes per year. introduced a correction in 1582 the was only slowly adopted by different nations over a period of centuries, but it is now by far the most commonly used calendar around the world.

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What Is Power With Example

Example1: Suppose, person A and B are assigned the task of picking up an equal number of boxes to the top floor of the building.

Lets say there are 10 boxes of 10 kg each to be picked up by both A and B. Each time they walk a distance of 5 m. Since the work done by both is in the form of potential energy mgh is given by,

W = mgh = 10 x 10 x 5 = 500 J is the work done by you both.

Suppose, A finishes his task in 50 s and B in 100 s.

As you can see the relationship of Work done per unit time is nothing but the Power.

So Power Work done

The rate at which work is done is referred to as power. It is always dependent on the work done. It is defined as the amount of energy that is converted per unit of time. Its International System of Unit is Watt which is equal to one joule per second. It is a scalar quantity.

For instance, a large amount of work is done and a large amount of fuel is consumed in a short period of time when a powerful car is accelerated rapidly.

Who Wants To Understand About Electricity And Its Source

Work, energy and power

Electric power refers to the rate per unit of time at which the electric energy is transferred by the electric circuit. If we talk about a unit of power, it is Joule per second or Joule per unit time. It is usually supplied to the homes or in the domestic mains electric supplies or in the offices. Electric power can be transferred to long distances with the help of transmission wires. This electric power is used for a number of purposes such as that in motion, light or heat with high efficiency.

Usually, electric power is produced by electric generators but they can be supplied to the source where it is needed with the help of the electric batteries. Electric power can be transferred to another form of energy when electric charges travel through a distance, which is popularly known as voltage. This basically occurs in electric components in the electric circuit. And on the basis of electric power, the circuits of electricity are further divided into two types. Those are active devices and passive devices.

Active devices are the sources of power while passive devices are the loads. You need to understand the law of electric power, which is the Ohms law. For the current to travel there is resistance also across the length of the wire test. It further depends upon different factors such as temperature, length of wires and so on. All the formulas, definitions, properties and other information need to be learnt well by the students.

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Calculating Power From Energy

What is the power output for a 60.0-kg woman who runs up a 3.00 m high flight of stairs in 3.50 s, starting from rest but having a final speed of 2.00 m/s?

Strategy and Concept


The woman does 1764 J of work to move up the stairs compared with only 120 J to increase her kinetic energy thus, most of her power output is required for climbing rather than accelerating.

It is impressive that this womans useful power output is slightly less than 1 horsepower size 12

! People can generate more than a horsepower with their leg muscles for short periods of time by rapidly converting available blood sugar and oxygen into work output. Once oxygen is depleted, power output decreases and the person begins to breathe rapidly to obtain oxygen to metabolize more foodthis is known as the aerobic stage of exercise. If the woman climbed the stairs slowly, then her power output would be much less, although the amount of work done would be the same.

Determine your own power rating by measuring the time it takes you to climb a flight of stairs. We will ignore the gain in kinetic energy, as the above example showed that it was a small portion of the energy gain. Dont expect that your output will be more than about 0.5 hp.

Power And Energy Consumption

We usually have to pay for the energy we use. It is interesting and easy to estimate the cost of energy for an electrical appliance if its power consumption rate and time used are known. The higher the power consumption rate and the longer the appliance is used, the greater the cost of that appliance. The power consumption rate is \, where \ is the energy supplied by the electricity company. So the energy consumed over a time \ is

Electricity bills state the energy used in units of kilowatt-hours \\), which is the product of power in kilowatts and time in hours. This unit is convenient because electrical power consumption at the kilowatt level for hours at a time is typical.

Example\: Calculating Energy Costs

What is the cost of running a 0.200-kW computer 6.00 h per day for 30.0 d if the cost of electricity is $0.120 per \?


Cost is based on energy consumed thus, we must find \ from \ and then calculate the cost. Because electrical energy is expressed in \ at the start of a problem such as this it is convenient to convert the units into \ and hours.


and the cost is simply given by


The cost of using the computer in this example is neither exorbitant nor negligible. It is clear that the cost is a combination of power and time. When both are high, such as for an air conditioner in the summer, the cost is high.

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Definition Of Power In Physics

Some of the definition of Power in Terms of Physics and Electricity are:

  • Electrical Power: The product of voltage and current.
  • Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.
  • Electric energy produced per unit time.
  • Current flowing through a poor conductor produces heat by an effect similar to mechanical friction. That heat represents energy that comes from the charge traveling across the voltage difference.

    Remember that separated charges have the potential to do work and provide energy.

    The work involved in heating a resistor is not very useful, unless we are making a hotplate rather it is a byproduct of restricting the current flow.

    Power is measured in unit of watts , named after James Watt, the Englishman who invented the steam engine, a device for producing lots of useful power.

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