The Energy Transfer Process & Solar Radiation

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  • 0:03 The Source of All Energy
  • 0:32 How Energy Is Transferred
  • 2:11 Radiant Energy
  • 3:52 Variations of…
  • 5:22 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Solar radiation is the reason that Earth is a hospitable planet for life. In this video lesson, you'll learn about this important energy source, as well as how energy is transferred and how this movement affects both regional and global temperatures.

The Source of All Energy

We take sunlight for granted, but we really shouldn't because essentially all energy on Earth comes from that big, bright star in the center of our solar system. And while we're at it, we should also give a shout-out to our atmosphere, because it absorbs some of that sunlight before it reaches us, as well as traps some of it for safe-keeping on the planet. This is an important balance - too much sunlight and Earth is too hot to live on, too little sunlight and Earth is not warm enough.

How Energy Is Transferred

What does pass through the atmosphere provides energy in many different forms, but before we get ahead of ourselves let's review the different ways that energy is transferred. When I was growing up, I listened to a band named CCR, which stands for Credence Clearwater Revival. And when I think of CCR I also think of energy transfer, because the three ways that energy is transferred between objects is also CCR: conduction, convection, and radiation! Even if you're not a classic rock fan you've got to admit that's pretty catchy!

Conduction is when energy is transferred between direct contact. When you burn your hand on a hot pan because you forgot to put on an oven mitt, that's conduction; the pan is transferring heat to your hand through direct contact. Likewise, when your feet touch the cold tile in the bathroom in the morning, your feet are transferring heat to the floor through direct contact - conduction in action!

Convection is when energy is transferred via currents in a fluid. This fluid could be a liquid or a gas, but the process is the same either way. When heat is applied to the fluid, the molecules near the heat become excited, spread apart, and become less dense so they are buoyed upward. When they cool, they fall back down again creating a cell-shaped current path.

Radiation is when energy is transferred in the form of electromagnetic waves. Think about sitting next to a campfire and feeling the welcome heat radiate from it to you - that's radiation! Radio waves, light waves, and heat waves can all travel like this, moving from one place to another without the help of any materials.

Radiant Energy

Let's put together what we know so far. First, we know that the energy comes from the sun, travels through space, then through our atmosphere, and finally reaches Earth's surface. We also know that this energy does not travel through any materials as it travels from the sun to the earth. If we put these two things together, we can deduce that it therefore must travel by radiation, and because of this we call it solar radiation. Energy that is emitted from the earth is called terrestrial energy.

Amazingly, every object or substance above absolute zero emits some energy via radiation. The amount of energy released is directly related to the temperature of the object or substance, and since the sun has a very high temperature it makes sense that it emits so much energy.

There is a flip side to this though, because all objects also absorb energy. The relationship here is the same as before; objects that are good at emitting radiant energy are also good at absorbing radiant energy. The earth is clearly not as good as the sun at emitting energy, which means it also can't absorb as much energy as it receives. And this is where the atmosphere becomes really important.

The atmosphere does let in radiation, but also acts as a blanket to keep much of it trapped on Earth, which keeps the planet warm. However, if the gases in the atmosphere become too abundant they may trap too much heat on Earth. These gases act like the walls of a greenhouse, which is why they are called greenhouse gases. But like a greenhouse, if there is no escape for the excess heat, then too much heat is trapped inside, and this can have detrimental effects on that temperature balance mentioned before.

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