What Is Energy Power Multiplied By Time?

Introduce Power and Energy

Power and energy are two related but distinct concepts in physics. Power refers to the rate at which energy is transferred or converted over time. It quantifies the ability to do work or generate heat.

Energy is the capacity to do work. There are different forms of energy such as thermal energy, radiant energy, kinetic energy, potential energy, chemical energy, nuclear energy and more. Energy comes in different forms that can be converted from one to another.

The relationship between power and energy is defined through their units. Power is measured in units like watts or horsepower, which quantify the rate of energy usage over time. Energy is measured in joules or kilowatt-hours, which quantify the total capacity to do work.

Power describes the speed of energy usage, while energy denotes the total amount. Power multiplied by time equals energy. A light bulb uses 100 watts of power. This means it uses 100 joules of energy every second. Over the course of an hour, it would use 100 watts x 3600 seconds = 360,000 joules or 360 kilojoules of energy.

Power Formula

The formula for power is:

P = E / t


  • P is power, measured in watts (W)
  • E is energy, measured in joules (J)
  • t is time, measured in seconds (s)

Power represents the rate at which energy is transferred or transformed per unit of time. In the power formula, E refers to the amount of energy transferred in joules, while t refers to the time duration in seconds.

So in plain terms, power is equal to energy divided by time. The power formula demonstrates the direct relationship between energy, time, and the rate of energy transfer (power).

Energy Formula

The formula for energy is:

E = P × t


E = Energy, measured in joules (J)

P = Power, measured in watts (W)

t = Time, measured in seconds (s)

So in the energy formula, energy (E) is equal to power (P) multiplied by time (t). Power is the rate at which energy is transferred or transformed. It is measured in watts. Time is the duration over which power is transferred or energy is used. It is measured in seconds.

To find the energy used or work done, you take the amount of power and multiply it by the time that power level is sustained. The longer the time, the more energy is used since power is energy per unit time.

Relationship Between Power and Energy

power x time = energy is a key relationship

Power and energy are related through a simple equation: power multiplied by time equals energy. This relationship allows us to calculate the amount of energy used or work done when we know the rate of power and the duration.

For example, a 60-watt light bulb uses 60 joules of energy per second. If the light bulb is on for one hour (3600 seconds), it will use 60 x 3600 = 216,000 joules of electrical energy in that time. The power (60 watts) multiplied by the time (3600 seconds) gives us the total energy used (216,000 joules).

As another example, a car engine’s power may be rated at 200 horsepower. If the car drives at that power output for 30 minutes, the amount of energy used would be 200 hp x (30/60) hours = 100 hp-hours. Again, the power multiplied by time gives the total energy.

This fundamental relationship allows us to interconvert between power and energy units and calculate one if we know the other. Understanding the link between power and energy is essential for energy management, electrical systems, physics calculations, and more.

Units of Power and Energy

Power and energy have standardized units that are used to measure them.

The standard unit of power is the Watt (W). Some common measurements of power in Watts include:

  • Lightbulb: 60W
  • Laptop: 45W
  • Microwave: 1000W

The standard unit of energy is the Joule (J). Some common measurements of energy in Joules include:

  • AA battery: 2500J to 5000J
  • 9V battery: 500J to 1000J
  • Banana: 200J

It’s important to note that Watts and Joules are equivalent units. By definition, 1 Watt = 1 Joule/second. This means that 1 Watt of power exerted for 1 second results in 1 Joule of energy.

So while Watts measure the rate of energy flow, Joules measure the total amount of energy. But they can be converted between each other based on time.

Power Over Time

One of the most important relationships between power and energy is how power measures the rate at which energy is transferred or converted per unit of time. In physics, power is defined as the amount of energy transferred or converted per unit of time. This means that power describes the speed or rate at which work and energy transfer occurs.

The units of power are joules/second, which are also called watts. So power measures the number of joules of energy being used, transferred, or converted every second. This speed or rate is an extremely useful metric across many scientific and engineering applications.

For example, an electric heater may be rated at 1500 watts. This means it can convert 1500 joules of electrical energy into 1500 joules of heat energy every second. The more power a device has, the faster it can do work or transfer energy.

Looking at power over time also helps calculate quantities like energy used. For instance, if a 100 watt light bulb is on for 5 hours, it uses 100 joules of energy per second for a total of 5 hours. By multiplying (100 joules/sec) x (60 sec/min) x (60 min/hr) x (5 hr), you get a total energy usage of 180,000 joules or 180 kilojoules.

So in summary, power describes the rate of energy transfer, while energy examines the total amount. Their relationship over time is crucial for understanding many everyday electrical and mechanical systems.


Here are some examples calculating power, energy and time:

Let’s say a lightbulb uses 100 watts of power. We can calculate the energy used by the lightbulb over a certain amount of time:

Power (P) = 100 watts

Time (t) = 5 hours

Energy (E) = Power x Time

= 100 watts x 5 hours

= 500 watt-hours

In this example, if the 100 watt lightbulb is left on for 5 hours, it will use 500 watt-hours of energy.

As another example, let’s say you need 10,000 joules of energy to heat up an object. You have a heater that provides 500 watts of power. How long will it take for the heater to produce 10,000 joules?

Power (P) = 500 watts

Energy (E) = 10,000 joules

Time (t) = E/P

= 10,000 joules / 500 watts

= 20 seconds

So with 500 watts of power, it will take 20 seconds to produce 10,000 joules of energy. This demonstrates the relationship between power, energy and time.


The power-energy-time relationship has many practical applications in physics and engineering. Here are some examples:

Electricity and Electronics

In electrical engineering, power (watts) equals voltage multiplied by current. Energy (joules) equals power multiplied by time. This allows calculating electric energy consumption and billing.

Mechanical Engineering

In mechanics, power is force multiplied by velocity. Kinetic energy equals 0.5 times mass multiplied by velocity squared. The power-energy-time formula allows calculating power consumption and energy transfers in machines and motors.


In thermodynamics, power measures the rate of heat transfer or work done. Energy is measured in joules of heat or work. The relationship allows analyzing power plants, heat engines, refrigerators, and more.


In optics, power is the radiant flux and energy is the total radiation. This allows calculating laser power outputs and energy levels.

Overall, the ability to relate power, energy, and time is crucial for modeling and evaluating energy usage across many scientific and engineering disciplines.


The power-energy-time relationship is fundamental in physics because it connects three of the most important concepts in describing motion and the behavior of physical systems. Power and energy are intrinsic properties of systems while time offers a way to observe and measure changes in those properties.

Specifically, the relationship P=E/t mathematically links power, energy, and time. This formula demonstrates that power is the rate at which energy is transferred or transformed per unit of time. As such, it provides a quantitative means to analyze and calculate how different forms of energy are converted in physical interactions.

Knowing how power, energy, and time are related allows physicists and engineers to predict and optimize the performance of designs and devices. For example, power output over time is a key metric for engines and generators. The P=E/t formula can help size components and systems to produce a desired power level.

On a fundamental level, the connection between power, energy, and time is essential to describing motion. Energy considerations dictate what states a system can occupy and how it evolves between states. Power characterizes the rate of that evolution. And time steps provide a reference to assess changes in state.

In summary, the relationship between power, energy, and time sits at the foundation of many crucial physical principles and quantitative analyses. It links the abstract quantities of power and energy to the concrete progression of time. For this reason, the power-energy-time relationship is indispensable for describing and predicting the behavior of systems in our universe.


In summary, power and energy are related but distinct concepts.

Power is the rate at which work is done or energy is transferred. It is measured in watts. The formula for power is:

Power = Work/Time


Power = Energy/Time

Energy is the capacity to do work. It is measured in joules. The formula for energy is:

Energy = Power x Time

So in essence, power is energy divided by time, while energy is power multiplied by time. The key is that power measures the rate at which energy is used or transferred, while energy measures the total amount.

We looked at examples like lightbulbs, motors, and batteries that illustrate the relationship between power (watts) and energy (joules or watt-hours). Understanding this relationship is important for measuring electrical usage and designing electrical devices and systems.

In summary, power and energy are intrinsically tied together through the dimension of time. Their formulas allow us to convert between power used or transferred per unit time, and total energy consumed or stored.

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