Useful Energy Relations | Do the Math
The familiar unit, the Watt, is simply Joules per second. A W incandescent light bulb is spewing J of energy per second in the form of. We all know the "Watt" is a unit of power consumption and have an idea how quickly a Watt kettle boils water. The unit of energy is the "Joule" - a Watt is . Understand the relationships between energy, work and power. Students gain an intuition for what joules and watts feel like by doing work and generating.
Power is nothing more than the rate at which energy is used. The familiar unit, the Watt, is simply Joules per second.
How to convert joules to watts
A W incandescent light bulb is spewing J of energy per second in the form of light and heat. It does not make sense to talk of Watts per second or Watts per hour. Watts is already a speed of energy consumption, not an energy unit on its own.
I like to think of power as being like what your speedometer tells you: The odometer is then the energy analog: Or if you think of energy as being like money, then power is the rate at which you spend or make money: We cover power here so that the widely used unit of energy called the kilowatt-hour can be understood.
Joule - Wikipedia
This is not kilowatts per hour, but kilowatts times hours. A kilowatt-hour is the amount of energy accumulated by running something at W for one hour seconds. Or it could be watts for ten hours.
In any case, it reduces to 3, J e.
Logarithmic scale of energy units, and useful conversions. The figure above lays out energy units on a logarithmic scale, covering about 27 orders of magnitude.
Memorizing these numbers will allow you to convert arbitrarily between units as needed. A few notes on each one: Light quanta photonsthermal energy per particle, and chemical reaction energies per molecule are conveniently expressed in eV.
Useful Energy Relations
For instance, visible light photons have energies around 1. Thermal energy per particle e. Chemical reactions per molecule tend to be in the 0.
The official definition of the Joule may still leave some uneasy. To clarify the magnitude of one Joule I will use the example of a conventional Watt incandescent light bulb. A light bulb rated at a Power of Watts will use Joules of Energy per second that it is operating. Another way to demonstrate the quantity of energy in one Joule is to think of how much energy is required to bring one liter [think of a Nalgene bottle] of water from room temperature 20 degrees Celsius to a boil degrees Celsius.
This would requireJoules.
Power and Energy • A Source of Confusion
So as you can see, one Joule is actually a fairly small amount of energy. Why is it confusing?how to convert watts to joule - electrical videos
Now that we have an understanding of energy and power we can address the basic misconception between the two. Power is a rate of energy use, and is usually expressed in Watts [W]. Where the confusion comes in is when we use the term kilowatt-hour to express units of energy, which is however correct. One kilowatt-hour is equivalent to the amount of Energy consumed when a device using energy at a rate of 1 kW is operated for one hour, in other words, Joules per second being used for seconds, resulting in a total energy use of 3, Joules.
Here are two examples: Imagine if you take 2 hours to clean your room with a vacuum cleaner that says: In full sun conditions, the array receives about Joules per second or: How much energy is stored in the battery after a day of 5 full sun hours?