Energy = f(Power,Time)

The Energy calculator computes the change in energy (ΔE) based on the power (P) and the time duration (Δt).

INSTRUCTIONS: Choose units and enter the following:

• (P) This is the constant power expended during the time.
• (Δt) This is the change in time.

Energy (ΔE): The calculator returns the change in energy in kiloWatt-hours.  However, this can be converted to compatible units (e.g. Joules) via the pull-down menu.

The Math / Science

The formula for the change in energy due to power is:

          ΔE = P * Δt

where:

• P is the constant power expended during the time.
• Δt is the change in time.

Power is the amount of energy consumed or produced over time.

• Power is a measurement of the energy used to move vehicles (automobiles, trucks, tractors, trains, boats and airplanes).
• Power is the measurement of energy consumed by a motor and transferred to the drive or wheels. 
• Power is the amount of electrical energy consumed or produced by a system over time such as the energy produced by a hydroelectric dam or energy consumed by an electrical motor.

Power Units

Power is most commonly measured in watts (W).  One watt is equal to one joule per second (1 W = 1 J / 1 s).  Power is also measured in horsepower (hp) where 1 horsepower equals 745.7 watts.  Power is also measured in heat energy transfer as BTUs per hour (BTU/h).

Power Calculators

• Power from Change in Energy over Time
• Power based on Force and Velocity
• P = ΔE / Δt
• ΔE = P * Δt
•  Δt = ΔE / P 
• Power Dissipated by Friction
• Power from Force, Distance and Time
• Power from Resistance and Current
• Power from Voltage and Resistance
• Power from Current and Voltage
• Power textbook chapter (Light and Matter)

Applications

How much energy in kilowatt hours does a light bulb use with time?

1. Enter the lightbulb's wattage (e.g. 200 watts) in the power field.
2. Choose time units (e.g. hours)
3. Enter the time duration (e.g. 24 hours)
4. Energy in Joules is returned (e.g. 17,280,000 Joules)
5. Click on the J unit button and select kWh
6. 4.8 kWh is returned.