Power - Meaning, Unit, Formula, FAQs

Power in physics refers to the amount of work done or energy transferred per unit of time. It is expressed in watts (W) and a watt is the equivalent of one joule per second. Power measures, how fast the energy is used or converted to another form. In electrical systems, for e.g. power = voltage x current (in a charge-neutral case, what this really tells you is how much electrical energy is being consumed, or being pumped, per unit of time. Power is important in running the various types of equipment and machines we use in everyday life. Generally, the higher the power rating, the more work a device can do in less time.

JEE Main 2025: Physics Formula | Study Materials | High Scoring Topics | Preparation Guide

JEE Main 2025: Syllabus | Sample Papers | Mock Tests | PYQs | Study Plan 100 Days

NEET 2025: Syllabus | High Scoring Topics | PYQs

This Story also Contains

1. Define Power
2. Solved Example Based on Power
3. Conclusion

LiveJEE Main 2025 Live: Exam city slip soon at jeemain.nta.nic.in; admit card date, cut-off updatesDec 30, 2024 | 10:30 PM IST

Candidates can have a look at the JEE Main 2025 physics syllabus below.

JEE Main 2025 physics topics	Number of questions	Marks
Modern Physics	5	20
Heat and Thermodynamics	3	12
Optics	3	12
Current Electricity	3	12
Electrostatics	3	12
Magnetics	2	8
Unit, Dimension and Vector	1	4
Kinematics	1	4
Laws of Motion	1	4
Work, Power and Energy	1	4
Centre of Mass, Impulse, and Momentum	1	4
Rotation	1	4
Gravitation	1	4
Simple Harmonic Motion	1	4
Solids and Fluids	1	4
Waves	1	4
Electromagnetics Induction; AC	1	4

Read More

In this article, we are going to read about power and different types of power and also see some solved examples, which belong to the chapter work, energy, and Power, which is one of the important chapters in Class 11 physics. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE and more. Over the last ten years of the JEE Main exam (from 2013 to 2023), more than fifteen questions have been asked on this concept. And for NEET almost six questions were asked from this concept.

Let's read this entire article to gain an in-depth understanding of the concept of power.

Define Power

Power is defined as the rate at which work is done or energy is transferred.

Dimension- ML2T−3

Units - Watt or Joule/sec (in SI), Erg/sec (in CGS)

Average power

Pav=ΔwΔt=∫0tp⋅dt∫0tdt

Instantaneous power

P=dwdt=P=F→⋅v→

Where, F→→ force v→→ velocity

Power is expressed as the rate of change of kinetic Energy

P=dkdt

Where,

dk→ change in kinetic energy dt→ interval of time

i.e. power is equal to the scalar product of force with velocity

Recommended Topic Video

Solved Example Based on Power

Example 1: An engine of a car of mass m = 1000 Kg changes its velocity from 5 m/s to 25 m/s in 5 minutes. The power (in KW) of the engine is

1) 5

2) 2

3) 1

4) 4

Solution:

Power expressed as the rate of change of kinetic Energy -

Power = Work done / time = change in K.E / time

Power = dk/dt

P=12m[(25)2−(5)2]5×60=12×1000×6005×60=1000 WP=1KW

Hence, the answer is the option (3).

Example 2: A constant power-delivering machine has towed a box, which was initially at rest, along a horizontal straight line. The distance moved by the box in time 't' is proportional to :

1) t2/3
2) t
3) t3/2
4) t1/2

Solution:

Power delivered by machine is, P

Force acting on the machine, F

\text { As we know, } P=\vec{F} \cdot \vec{V}

As force and velocity have the same direction the angle between force and velocity is

So P=FV
or P=maV=mdVdtV
Given that the machine is delivering constant power.
So P=C (constant)
P=C
FV=C
MdVdtV=C

Integrating both sides, we get

V22∝tV∝t1/2dxdt∝t1/2 Again integrate both sides x∝t3/2

Hence, the answer is the option(3).

Example 3: Sand is being dropped from a stationary dropper at a rate of 0.5 kg−1 on a conveyor belt moving with a velocity of 5 ms−1. The power needed to keep the belt moving with the same velocity will be :

1) 1.25 W
2) 2.5 W
3) 6.25 W
4) 12.5 W

Solution:

The power needed to keep the belt moving with the same velocity will be

P=(dmdt)v2=(0.5)×25P=12.5 W

Hence, the answer is the option (4).

Example 4: A particle of mass M is moving in a circle of fixed radius R in such a way that its centripetal acceleration at time t is given by n² R t² where n is a constant. The power delivered to the particle by the force acting on it is:

1) Mn2R2t
2) MnR2t
3) MnR2t2
4) 12Mn2R2t2

Solution:

Centripetal acceleration, ac=n2rt2 where, ac=v2r
⇒v2r=n2rt2⇒v=nrt…
tangential acceleration, at=dvdt=nr…
Tangential force acting on the particle, F=Mat=Mnr
Power delivered, P=F→⋅v→=Fvcos⁡θ
∴P=Fv=(Mnr)×nrt(∵θ=0∘)⟹P=Mn2r2t

Hence, the correct option is option 1.

Example 5: Sand is being dropped from a stationary dropper at a rate of 0.5 kg−1 on a conveyor belt moving with a velocity of 5 ms−1. The power needed to keep the belt moving with the same velocity will be :

1) 1.25 W
2) 2.5 W
3) 6.25 W
4) 12.5 W

Solution:

The power needed to keep the belt moving with the same velocity will be

P=(dmdt)v2=(0.5)×25P=12.5 W

Hence, the answer is the option (4).

Conclusion

Power in physics is the rate at which work is done or energy is transferred, measured in watts (W), which is equivalent to one joule per second. It can be calculated as the product of voltage and current in electrical systems and as the rate of change of kinetic energy in mechanical systems. Power is crucial for efficiently operating various equipment and machines. Understanding power is essential for exams like JEE Main and NEET, where multiple questions are often asked on this concept.