Continuous Spectrum: Definition & Overview

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  • 0:00 What Is a Continuous Spectrum?
  • 0:37 The Electromagnetic Spectrum
  • 1:17 The Sun
  • 1:44 Absorption Spectrum
  • 2:23 Emission Spectrum
  • 3:02 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

If you've seen a rainbow, you may have seen a continuous spectrum - or something close to it. In this lesson, you'll learn about continuous spectra in the context of the electromagnetic spectrum and light. You'll also learn about two types of spectra that aren't continuous: absorption spectra and emission spectra.

What Is a Continuous Spectrum?

When you shine white light through a prism, you find out that it contains a rainbow of colors. This is called dispersion, and it happens because light of different wavelengths, or colors, refracts, or bends, by different amounts inside the prism.

The rainbow could be described as a spectrum, and if the spectrum goes all the way from red to violet, with no gaps, then it is a continuous spectrum. A beam of perfectly white light, like you would get under certain laboratory conditions, contains this kind of spectrum. You can create a continuous spectrum by heating up a material until it glows. But as we will find out, most light - even the light from the sun - does not contain a continuous spectrum!

The Electromagnetic Spectrum

White light might be a continuous spectrum, but it's only part of the electromagnetic spectrum. There are more wavelengths than we can see with our human eyes. A wider continuous spectrum would include radio waves, microwaves and infrared, ultraviolet, x-rays, and gamma rays. As far as we know, no object in the universe sends out waves across the whole of the electromagnetic spectrum, so finding a continuous spectrum spanning the whole of the electromagnetic spectrum would be impossible.

The following diagram shows the full electromagnetic spectrum and everything it contains.

The energy of waves increases from left to right across the electromagnetic spectrum.

The Sun

The sun is extremely bright and gives off an immense amount of energy, but it turns out that it isn't even close to giving off a truly continuous spectrum. Even though we do see a rainbow when light is refracted after it rains, when we look at the Sun's light and analyze it in detail, we find that there are gaps where we see nothing at all!

When we take the Sun's light and put it through a spectrometer, a device that separates light by wavelength, the sun's spectrum looks something like this:

Absorption Spectrum

The gaps in the Sun's spectrum are called absorption lines, and they give us valuable information about the sun. Here's how it works:

The sun contains elements like hydrogen and helium. When the sunlight, including ultraviolet and infrared that we can't see, shines through these elements, they absorb the energy, but they only absorb electromagnetic waves that are just the right color to match the energy they need. This gives us those gaps in the sun's spectrum.

 Absorption Spectra

Each element in the universe has a different combination of absorption lines, so we can use the sun's absorption spectrum to figure out what elements are present in the sun. This is how we know what the sun's made of.

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