• Engineering and Architecture
  • Management and Business Administration
  • Medicine and Allied Sciences
  • Law
  • Animation and Design
  • Media, Mass Communication and Journalism
  • Finance & Accounts
  • Computer Application and IT
  • Pharmacy
  • Hospitality and Tourism
  • Competition
  • School
  • Study Abroad
  • Arts, Commerce & Sciences
  • Learn
  • Online Courses and Certifications
Unit of Power - Definition, Unit, FAQs

Unit of Power - Definition, Unit, FAQs

Team Careers360Updated on 02 Jul 2025, 04:59 PM IST

Introduction

Power is the measurement of doing work per unit time. Let us answer the question what is the unit of power? The SI unit of power is watt, which was given after the Scottish physicist James watt. To measure the capability of his modified steam engine, James watt discovered another unit of power which is horse power unit. But the unit commonly used to express the power of an engine is Watt, which is the practical unit of power. Let's move forward in order to fully grasp and understand what the unit of power is.

Commonly Asked Questions

Q: How is power relevant in thermodynamics?
A:
In thermodynamics, power is often considered in terms of heat transfer rates or the rate of work done by or on a system. It's crucial in analyzing heat engines, refrigeration cycles, and other thermal processes.
Q: What is meant by 'power hungry' in the context of electronic devices?
A:
Power hungry' refers to devices or systems that consume a large amount of power relative to their function or compared to similar devices. This often implies lower efficiency or the need for more robust power supply systems.
Q: How does altitude affect engine power?
A:
Engine power typically decreases with increasing altitude due to lower air density. This results in less oxygen available for combustion, reducing the engine's ability to produce power.
Q: How does gearing affect power in mechanical systems?
A:
Gearing can change the balance between force and velocity in a mechanical system, but it doesn't change the overall power. Lower gears provide more force but less speed, while higher gears do the opposite, maintaining the same power output.
Q: How does power relate to the concept of energy conservation?
A:
The principle of energy conservation states that energy cannot be created or destroyed, only converted from one form to another. Power describes the rate at which this energy conversion occurs, always adhering to the conservation principle.

What is power?

Commonly Asked Questions

Q: What is power in physics?
A:
Power in physics is the rate at which work is done or energy is transferred. It measures how quickly energy is used or converted from one form to another.
Q: How is power related to work and time?
A:
Power is directly related to work and inversely related to time. It can be calculated by dividing the amount of work done by the time taken to do that work: Power = Work / Time.
Q: Can power be negative?
A:
Yes, power can be negative. Negative power indicates that energy is being absorbed or received by a system, rather than being expelled or done by the system.
Q: Why is power important in real-world applications?
A:
Power is crucial in real-world applications because it helps us understand how quickly energy is being used or transferred. This is important for designing efficient machines, managing energy consumption, and optimizing performance in various systems.
Q: How does power relate to efficiency?
A:
Power relates to efficiency in that a more efficient system will require less power to perform the same amount of work. Efficiency is often expressed as the ratio of useful power output to total power input.

measure of work done per unit time.

Also check-

Power is the defined as the rate at which electrical energy is consumed in an electrical circuit or amount of work done per unit time.

P=WT

Where,

  • P is the power

  • W is the work done

  • T is the time taken

Also, P=dWdT=d(F. r)dT

Where, w = F. r = force x displacement

P= F. drdT

P= F. V

Where, V=drdT=velocity

From P=WT

Unit of power in SI unit is =joulessecond = watt

From the above equation, we can say that the series of basics and physics that are making this work has prequels and sequels, concept that depend on each other and is going to help us understand it better. Joules depend on newton and watt which is the unit of power depends on joules.

Watt is exceedingly simple to understand. It is basically how much energy is used over an amount of time. Hence we can say that, if we spend one joule of energy in one second then that yield one watt.

And from

P= F. V

The unit of power is = ms-1 = kgm2s-3

Differential mathematical forms of electric power:

P=WT

Potential difference V = WQ

So, W = V.Q

P=VQT

From ampere’s law, I=QT

So

P = V.I

Now according to ohm’s law V=IR

So,

P = I2R

Related Topics Link,

NEET Highest Scoring Chapters & Topics
This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.
Download E-book

Unit of Power

The unit of power in SI unit is Watt. This name was given by a Scottish scientist James watt. He became very famous because of his contribution in improving the steam engine in 1781.

watt unit is nemed after the scottish inventor james watt

Let us now define unit of power: Watt

Watt can be defined as the power of appliance which does work or consumes energy at the rate of 1 joule per second. Watt is the measurement of how fast the work is done. The abbreviation for watt is W. Time doesn’t matter in the definition of joule, it is just getting the job of moving an object using one newton of force over one meter. If we use one newton force and we complete one meter distance, no matter how long the task took it is said to have one joule energy. Similarly the Power is simply where time matters and is taken into account and this can be seen in the expression joule per second which is a watt. Watt is used in electrical work. Any power of an electrical appliance tell the rate at which the energy is consumed. So, the power of an electrical appliance is defined in terms of watt. For example, a bulb of 30 watt tells us that it consumes the electrical energy at the rate of 30 joule per second.

Now to understand it better or relate to it let’s take a look at an example:

Let us suppose a man pushes a cart from point A to point B with an energy of one joule. If he covers the distance from point A to point B in one second then he spent one watt of power and if he take two second to cover the same distance then he only produces half(0.5) a watt because it took him twice as long to accomplish the task. Hence we can conclude that the less time it takes to accomplish the task, higher will be the power.

Commonly Asked Questions

Q: What is the SI unit of power?
A:
The SI unit of power is the watt (W), named after James Watt. One watt is equal to one joule of energy transferred per second.
Q: What is the concept of power density?
A:
Power density is the amount of power per unit volume or mass. It's an important consideration in designing compact or lightweight power systems, such as in mobile devices or vehicles.
Q: What is meant by 'rated power' in electrical devices?
A:
Rated power refers to the power consumption or output that a device is designed to handle under normal operating conditions. It's typically specified by the manufacturer and indicates the device's capacity.
Q: How does temperature affect power output in solar panels?
A:
Generally, the power output of solar panels decreases as temperature increases. This is due to increased resistance in the semiconductor materials, highlighting the importance of cooling in solar energy systems.
Q: What is the difference between mechanical and electrical power?
A:
Mechanical power involves the rate of doing physical work, often through motion or force application. Electrical power relates to the rate of electrical energy transfer. While the underlying concept is the same, they are measured and applied differently in practice.

How do we exert one watt power?

  • The work done to lift a 102g (0.102 kg) through a distance of one meter in one second.

We know,

P=WT =f.dT =m.g.dT

Where, P = power, T= time taken, W= work done, f= force, m= mass,

g is equivalent to acceleration due to gravity, d= distance

After putting the values,

P=0.102 kg.9.81m/s^2 .1m1 s

P=1 Watt

Let’s take a look at another example,

How much do I do on my body when I do one pull up? Assume I raise 60 cm (0.60 m) and I have a mass 95 kg. It takes me 0.5 seconds.

We know,

P=WT =f.dT =m.g.dT

Where, P = power, T= time taken, W= work done, f= force, m= mass,

g is equivalent to acceleration due to gravity, d= distance

After putting the values,

P=95kg.9.81m/s^2 .0.60 m 0.5 s

P=1120 Watt

Now if we are clear with the unit watt let’s see another unit of power which is Horsepower unit.

1 horsepower is equivalent to 746 watt.

We measure a power of engine especially the car engine in horsepower. Before cars, trains and buses, horses were the primary vehicle for transportation and for any other commercial work. Horses were widely used for all kinds of power in 18th century and earlier. So, how much power is there in a horsepower? How horsepower came to be one of the most common ways that we measure the power of car engine? Horsepower is the unit of power. Well, the history of the horsepower goes back to the 18th century and the Scottish inventor, James Watt, is a reason behind this unit. The first commercial stem powered device is generally considered to be Thomas Savery’s steam pump which invented in 1698. By 1712, Thomas Newcomen had created a steam engine that could transmit continuous power. Both these early designs were primarily used to pump water for mines. The Newcomen engine was significantly more powerful and replaced the team of 100 horses that have been used to pump water out of a mine. In 1758, the Newcomen engine came to the attention of James Watt a Scottish inventor and mechanical engineer, who made a living by fixing and making scientific and mechanical instrument in Glasgow Scotland. He came up with the term horsepower and coined the horsepower unit. Hence we got, 1 horsepower is equivalent to 746 watts which is 0.746 kilowatts

Also Read:

Commonly Asked Questions

Q: How is power related to force and velocity?
A:
Power can be expressed as the product of force and velocity: Power = Force × Velocity. This relationship is particularly useful in situations involving constant motion.
Q: What is the formula for electrical power?
A:
The formula for electrical power is P = VI, where P is power in watts, V is voltage in volts, and I is current in amperes.
Q: How does power relate to the concept of work in physics?
A:
Power is the rate at which work is done. While work measures the total energy transferred, power tells us how quickly that transfer occurs. The relationship is: Power = Work / Time.
Q: How does power factor affect electrical power in AC circuits?
A:
Power factor is the ratio of real power to apparent power in AC circuits. A low power factor means that a significant portion of the apparent power is not doing useful work, reducing efficiency and potentially increasing costs.
Q: What is instantaneous power?
A:
Instantaneous power is the power at a specific moment in time. It's particularly useful when dealing with systems where power output varies over time, such as in alternating current circuits.

Other generally used units of power

Following are the all units of power:

  • Horsepower, abbreviated as HP and is equivalent to 746 watts.

  • Kilowatts, abbreviated as kW and is equivalent to 1000 watts or 103 watts.

  • Megawatts, abbreviated as MW and is equivalent to 1000000 watts or 106 watts.

  • Gigawatts, abbreviated as GW and is equivalent to 1000000000 watts or 109 watts.

  • Decibel-milliwatts, abbreviated as dBm and is equivalent to 1Watt = 30 dBm.

  • British thermal unit, abbreviated as BTU and is equivalent to 1Watt = 3.412 BTU/hr.

  • Calories per second, abbreviated as cal/sec and is equivalent to 1Watt = 0.2 calories per second

Also read -

NCERT Physics Notes:

Commonly Asked Questions

Q: What is the relationship between horsepower and watts?
A:
Horsepower and watts are both units of power. One horsepower is approximately equal to 745.7 watts. This relationship allows for conversion between the two units.
Q: How does power consumption relate to energy bills?
A:
Energy bills are typically based on the amount of electrical energy consumed, which is power multiplied by time. Higher power consumption over time leads to higher energy usage and, consequently, higher bills.
Q: How is power measured in practice?
A:
Power can be measured using various instruments depending on the context. For electrical power, wattmeters are used. In mechanical systems, dynamometers can measure power output. In some cases, power is calculated from measurements of other quantities like force, velocity, voltage, and current.
Q: What's the difference between power and energy?
A:
Energy is the capacity to do work, while power is the rate at which that energy is used or transferred. Energy is measured in joules, while power is measured in watts (joules per second).
Q: What is the power equation in terms of torque and angular velocity?
A:
For rotational motion, power can be expressed as the product of torque and angular velocity: Power = Torque × Angular Velocity. This is useful in analyzing rotating machinery.

Frequently Asked Questions (FAQs)

Q: How does the concept of power relate to the expansion of the universe in cosmology?
A:
In cosmology, power is relevant in understanding the energy dynamics of the expanding universe. Concepts like the power spectrum of cosmic microwave background radiation provide crucial information about the early universe and its evolution.
Q: What is the significance of power in the study of black holes?
A:
In the context of black holes, power is relevant in understanding phenomena like Hawking radiation and the energy released during matter accretion. The immense gravitational power of black holes makes them some of the most energetic objects in the universe.
Q: How does power relate to the concept of force fields in physics?
A:
In the context of force fields, power can be thought of as the rate at which work is done on a particle moving through the field. The power depends on both the strength of the field and the velocity of the particle.
Q: How does the concept of power apply in fluid dynamics?
A:
In fluid dynamics, power is often considered in terms of the rate of energy transfer in fluid flows. This is crucial in understanding phenomena like turbulence, drag, and the efficiency of hydraulic systems.
Q: What is the relationship between power and information in physics?
A:
The relationship between power and information is explored in fields like information theory and quantum computing. For example, Landauer's principle relates the erasure of information to a minimum amount of energy dissipation, connecting information processing to power consumption.
Q: How does power consumption change in superconducting materials?
A:
Superconducting materials have zero electrical resistance, which means they can conduct electricity with theoretically zero power loss. This property has significant implications for power transmission and high-efficiency electrical systems.
Q: What is the significance of power in statistical mechanics?
A:
In statistical mechanics, power can be related to the rate of energy transfer between microscopic states. This concept is important in understanding non-equilibrium thermodynamics and the behavior of complex systems.
Q: How does power relate to the intensity of sound waves?
A:
The intensity of a sound wave is the power transmitted per unit area. Higher power results in higher intensity, which we perceive as louder sound. The relationship is logarithmic, which is why we use the decibel scale for sound intensity.
Q: What is the concept of power spectral density in signal processing?
A:
Power spectral density describes how the power of a signal is distributed across different frequencies. It's a crucial concept in analyzing random processes, communication systems, and various types of noise.
Q: How does power factor correction work and why is it important?
A:
Power factor correction aims to bring the power factor of an AC electrical system closer to 1 by reducing reactive power. This is important because it improves efficiency, reduces energy costs, and helps maintain grid stability.
Articles
Previous
Next