How is Energy Measured?

ResidentialCalendarOctober 23, 2018

Your groggy face is lit with the low-wattage light from the fridge. You open this small door every morning in search of breakfast. Rarely do you think about all the energy involved in getting yourself to the kitchen and turning the lights on, or the energy keeping your food cool and preserved. Do you ever wonder, “How is energy measured?” 

Energy is easy to take for granted. We expect that when we flip a switch, the lights will go on. Waking up in the morning, your first impulse might be to make food or a hot cup of coffee. That’s all in pursuit of energy. It’s constantly working through and around you. 

Energy in its simplest form is the capacity to do work.1 This includes converting potential energy to usable energy. That means everything from the lightbulb in the fridge transforming an electrical current into light energy, to your body burning up the calories in your breakfast sandwich for energy to move and focus. 

Since energy has such an impact in every part of our lives, let’s explore a little more about it by looking at the different forms of energy and how they're measured. 

How are energy and temperature units measured?

Energy is a complex topic because there are different ways to measure it, depending on the application. Different types of energy include electrical, mechanical, chemical, thermal, and nuclear. We’ll focus mostly on thermal and electrical in this post. But, let’s start with an overview. 

To get science and engineering experts on the same page, the International System of Units (SI) was developed in 1960. Here’s a breakdown of the seven base units in the SI system.2

  • Meter - for measurement of length
  • Kilogram - for mass
  • Second - for time 
  • Ampere - for electric current
  • Kelvin - for temperature
  • Candela - for luminous intensity
  • Mole - for amount of substance

To zero in further, we’ll look at a few of the SI derived units that relate to electricity and power.3 Think of these as subsets based on the core units combined with other factors in physics.

  • Joule - used for energy, work, quantity of heat 
  • Watt - used for power 
  • Coulomb - used for electric charge or quantity of electricity

For electricity used to power devices, homes, or businesses, these are units that measure electric potential and electric current. 

  • Volt (V) - the standard unit of electric potential 
  • Ampere (A), or amp - the standard unit of electric current 

Units of thermal energy measured

Thermal energy relates to the differences in temperature between objects and the heat created when energy is transformed from one form into another. The calories in your breakfast sandwich fall under thermal energy since your body burns them up for fuel.

On a larger scale, a British Thermal Unit (BTU or Btu) is the energy content of fuel. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.

Combustion is what transforms the chemical energy of the fuel into thermal energy or heat. A therm (thm) equals 100,000 BTU and is about equal to the amount of energy released by burning 100 cubic feet of natural gas.4

Electrical energy (to power your home) measured

Electrical energy is based on the attraction and repulsion of charged particles. The intensity of the charge and the distance between particles produces voltage. 

Voltage creates an electrical current by moving electrons through a conductor. Once energy sources have gone through the needed combustion, transformation, or conversion to be used by us in our homes, it’s measured in kilowatt hours. 

Going back to the SI derived units, remember that a Watt is the unit of measurement for power. 

  • 1000 watts (W) = 1 kilowatt (kW) - measuring power

A kilowatt-hour is a measure of energy, which has been converted. This is what you see on your electric bill. The two can be a little confusing, so here’s an example of how kilowatts and  kilowatt-hours work together. 

If you have a 1000-watt microwave, that means it requires 1,000 watts (which is equal to 1 kW) to work. If you let your microwave run for one hour, you have used 1 kWh of energy.

Solar panels create electricity to power your microwave, fridge, and light bulbs by converting the sun’s light energy into an electrical current. It’s a unique way of making energy that doesn’t involve burning fuel, coal, or gas.

It’s a smart solution, using energy sources that won’t be exhausted, and is constantly improved for better efficiency. This is an exciting time to learn about energy and how it’s measured as the energy landscape itself undergoes a huge transformation.

 

Endnotes

1 https://www.greentechmedia.com/articles/read/energy-and-power-units-the-basics-8#gs.7QIxHag
2 http://www.npl.co.uk/si-units/
3 https://physics.nist.gov/cuu/Units/units.html
4 https://www.greentechmedia.com/articles/read/energy-and-power-units-the-basics-8#gs.7QIxHag

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