Education Journalist | Study Abroad Lead
The unit of Power is represented as Watt. In physics, power is referred to as the time rate of doing work or delivering energy, which is expressed as the amount of work done W (energy transferred), divided by the time interval t. A certain amount of work can be done either by a low-powered motor for a long time or by a high-powered motor in a short time.
- The unit of power is the watt (symbol: W).
- One watt is the amount of power required to do one joule of work in one second.
- If a device uses one watt of power, it consumes energy at a rate of one joule per second.
Key Terms: Power, Energy transfer, Unit of Power, Horsepower, CGS system, Energy, Joules, Work Done
What is Power?
[Click Here for Sample Questions]
Power is the rate at which energy is transferred or converted or the rate of doing work. Technically it is the amount of work done per unit of time. The SI unit of power is Watt (W) which is joules per second (J/s). Sometimes the power of motor vehicles and other machines is expressed in terms of Horsepower (hp), which is approximately equal to 745.7 watts.
- Power can also be related to other things or situations, for example, the power that helps various things move around.
- Power can also be described as the product of a specific force on an object and its velocity.
- It is a scalar quantity, which means that it gives us a quantity or amount of energy consumed per unit of time but with no indication of direction.
Power
Also Read:
Power Formula
[Click Here for Previous Year Questions]
Power is referred to as the rate at which work is done upon an object. It is a time-based quantity that is related to how fast a job is done. The formula for power is as below:
Power = Work/time
P = W / t
SI Unit of Power
[Click Here for Sample Questions]
The SI Unit of power is Watt (W). One joule of energy transferred in a second is equal to 1 watt.
1 Watt = 1 J/s = 1 kg-m2/s3
As the metric system is divided into base units and derived units, when we convert joules into base units we get ( kg-m2/s2 ). It is used to find out the conversion of watts into base units.
- Watt is named after James Watt, who was an 18th-century inventor who had invented and patented many important instruments by his name.
- Before Watt became the SI unit of power, Horsepower was used as a unit of power. But the horsepower is a very large unit, so to find a smaller unit of power, the unit watt was introduced.
- 1 Horsepower = 735.499 Watt
- The relation between units of Power:1 kW = 1000W, 1 MW = 1000000W and 1GW = 1000000000W
- In the MKS system, the unit of power is: kgm2s-3
- In the CGS system, the unit of power is erg per second.
- As power is needed to be measured in different areas of science and engineering. So to make things simpler there are many submultiples and multipliers of Watt.
Other Units of Power
ts of power Although the watt is the standard unit of power, other units are commonly used in various applications. Some of these units include horsepower, kilowatt, and megawatt.
- Horsepower is a unit of power commonly used in the automotive industry to describe the power output of engines. One horsepower is equal to 746 watts.
- Kilowatt is a unit of power commonly used in electrical applications. One kilowatt is equal to 1000 watts.
- Megawatt is a unit of power commonly used in power plants and other large-scale applications. One megawatt is equal to one million watts.
Also Read: Electrical Power Formula
Submultiples of Watt
[Click Here for Previous Year Questions]
Here are some important submultiples of Watt-
| Name of the unit of Power | Symbol | Value |
|---|---|---|
| Deciwatt | dW | 10-1W |
| centiwatt | cW | 10-2W |
| milliwatt | mW | 10-3W |
| microwatt | µW | 10-6W |
| nanowatt | nW | 10-9W |
| picowatt | pW | 10-12W |
| Femtowatt | fW | 10-15W |
| attowatt | aW | 10-18W |
| zeptowatt | zW | 10-21W |
| Yoctowatt | yW | 10-24W |
Also Read:
Multipliers of Watt
Here are the multipliers of Watts-
| Names | Symbol | Value |
|---|---|---|
| Decawatt | daW | 101 W |
| Hectowatt | hW | 102 W |
| Kilowatt | kW | 103 W |
| Megawatt | MW | 106 W |
| Gigawatt | GW | 109 W |
| Terawatt | TW | 1012 W |
| Petawatt | PW | 1015 W |
| Exwatt | EW | 1018 W |
| Zettawatt | ZW | 1021 W |
| Yottawatt | YW | 1024 W |
Units of Power in Other Systems and their Equivalent in Watts
[Click Here for Sample Questions]
Here is the relation of the Units of Power with other systems and their equivalent in Watts-
| Unit | Equivalent in Watt |
|---|---|
| Horsepower (Hp) | 746 W |
| British Thermal Unit (BTU) | 1 Watt = 9.47 * 10-4 BTU |
| Foot Pounds | 1 Watt = 0.737 foot-pounds |
| Calories per second | 1 Watt = 0.24 calories per second |
Also Read: Unit of Light
How to Measure Variable Power?
[Click Here for Previous Year Questions]
To measure variable power 3 methods are used:
- Instantaneous Power – This is the power measured at a given instance of time. For calculating such power high-level mathematical instruments are needed to be used.
- Average power – When power is measured for a long period of time, the average of it can find out. The average of power can find out by adding the power of different points of time and then dividing the sum with time.
- Peak Power – The maximum amount of instantaneous power a machine or system can reach, over a long period of time is called peak power. Peak power is much higher than average power and is maintained for a very short period of time to avoid any damage.
Uses of the Unit of Power
[Click Here for Sample Questions]
Here are the important uses of the Unit of Power-
- Unit of power can be used in other electrical measurements. Electrical measurements are usually done with the unit- Horses and 1 Watts is equal to 0.74549 Horses.
- While Voltage is usually measured with the unit of volts, we can solve other equations related to this with the unit of power because 1 Watt is equal to 1 volt.
- Measuring amperes can also be done with the measurement of power because 1 watt is equal to 0.001335 amperes.
Also Read:
Previous Year Questions
- Water falls from a height of 60 m at the rate of 15 kg/s… (NEET 2008)
- A particle of mass M, starting from rest, undergoes… (NEET 2010)
- A ball moving with velocity 2m/s… (NEET 2010)
- Two masses of 1 g and 9 g move with equal kinetic energies… (NEET 1993)
- A batsman hits back a ball straight in the direction of the bowler without… (NEET 1989)
- A bullet of mass 10 g leaves a rifle at an initial velocity of… (NEET 1989)
- On a frictionless surface, a block of mass MM moving at… (NEET 2015)
- Two particles of masses m1, m2 move with initial velocities...(NEET 2015)
- A particle moves from a point… (NEET 2016)
- A moving body of mass m and velocity… (NEET 1996)
Things to Remember
- Power is the rate at which energy is transferred or Converted or the rate of doing work.
- SI Unit of power is Watt; 1 Watt = 1 J/s = 1 kg -m2/s3
- 1 watt is equal to 1 joule of work done in 1 second.
- Watt is named after the famous inventor James Watt.
- Watt is a scalar quantity, which means it doesn’t contain direction.
- The formula for power is Power = Work / time; P = W / t.
- Other units of power, such as horsepower, kilowatt, and megawatt, are commonly used in various applications.
- In the MKS system, the unit of power is kgm2s-3
- In the CGS system, the unit of power is erg per second.
Sample Questions
Ques: State the relation between the units of power. (1 mark)
Ans: 1 kW = 1000W, 1 MW = 1000000W and 1GW = 1000000000W.
Ques: How big is Watt as compared to Joule? (1 mark)
Ans: Joule is very small as compared to Watt. Joule is the 3600th part of a watt-hour.
Ques: What is the biggest multiple of Watt? (1 mark)
Ans: The biggest multiplier of watts is yottawatt and it is 1024 times watt.
Ques: What is Horsepower? (2 marks)
Ans: Horse Power (HP) is another unit of Power, which is largely used in mechanical engineering. It is also useful in describing the output of automobiles, motorbikes, aeroplanes, etc.
Ques: Explain in depth why there are so many multiples and submultiples of Watt. (3 marks)
Ans: The application of the concept of power is everywhere from atomic science to rocket science, from drones to fighter jets, so when some concept is applied to so many differing areas you can not standardize the same unit for every area of use. To facilitate research watt is selected as a unit of power, which is a unit quantity of power, and to facilitate usability many micro and macro units are also defined in terms of a watt.
Ques: What is the unit of power used in electric physics? (2 marks)
Ans: In electro physics, the power is equal to the voltage multiplied by charge and divided by time.
P = V.Q/T
Where
V = voltage , SI unit = Volt
Q = Charge , SI unit = Coulomb
T = Time , SI unit = second
So the unit of power in electro physics will be v.c/s.
Ques: A 60-watt bulb is switched on 24 hours per day and there is another 60-watt bulb that is turned on for only 12 hours. Calculate the energy consumed by both bulbs in one day. (4 marks)
Ans: For the first 12 hours, both bulbs A and B are turned on, thus,
Power = 60 + 60 = 120 watts
Energy = Power x Time
= 120 x 12
= 1.44 kWh (kilowatt-hour)
Now, for the next 12 hours, only bulb A would remain on, therefore,
Power = 60 watts
Energy = 60 x 12 = 0.72 kW h
Now,
Average Power = Total energy consumed / Total time taken
Therefore, the average power for our light bulbs will be,
= (1.44 + 0.72) / 24
= 0.092 kW
Ques: State and define the SI unit of power. (2 marks)
Ans: The SI Unit of power is Watt (W). One joule of energy transferred in a second is equal to 1 watt.
1 Watt = 1 J/s = 1 kg -m2/s3
As the metric system is divided into base units and derived units when we convert joules into base units we get (kg -m2/s2). Which is used to find out the conversion of watts into base units.
Ques: How can varying power be measured? (3 marks)
Ans: The measurement of varying power depends on the specific context and application. In general, power is the rate at which energy is transferred or used over time, and it is often measured in watts (W).
If you want to measure the power of a fluctuating electrical signal, you can use an oscilloscope or a power meter that is designed to measure AC (alternating current) power. These devices can give you a real-time reading of the instantaneous power of the signal.
If you want to measure the power output of a machine that operates over a range of speeds or loads, you may need to use a dynamometer or a similar device that can measure torque and rotational speed. From these measurements, you can calculate the mechanical power output of the machine.
In some cases, you may need to measure the power consumption of a device or system, which can be done using a wattmeter or similar device. This can help you determine how much energy is being used over a given period of time.
Overall, the specific method for measuring varying power will depend on the type of power being measured and the specific application.
Ques: What is Joule? (3 marks)
Ans: Joule refers to the SI unit of work or energy which is equal to work done by a force of 1 Newton to move the point of application, 1 m in the direction where the force is acting. 1 Joule is equivalent to 3600th of a watt-hour and is approximately the amount of energy required to lift an apple against the Earth’s gravity by a distance of 1 m.
Also Read:
Comments