![]() ![]() The visible light spectrum, composed of electromagnetic waves with λs between 400nm and 750nm, falls right in between the two divisions described above. You may have noticed a rather significant omission in the litany of waves thus far considered: visible light. However, the effects of any electromagnetic wave depend to some extent on its intensity - the amount of power it delivers per unit area (i.e., how much energy the wave transfers to a given area in a given amount of time). ![]() X-rays pose a much greater threat to your general wellbeing than radio waves because any given x-ray photon has much greater energy (great enough, in fact, to break bonds in DNA) than any given radio wave photon. ![]() We should consider here, though, that this is why the short- λ electromagnetic waves tend to have a rather worse reputation than those at the longer end of the spectrum. Modeling electromagnetic waves in this quantum way (each photon of a particular wavelength has a particular amount - a quantum - of energy) has very interesting and practical applications, some of which we’ll explore in subsequent sections. We describe them using the photon model - we treat short-wavelength electromagnetic waves as a collection of discrete packets of energy ( photons). Interestingly, these waves in fact have more particle-y than wave-y characteristics. These species of electromagnetic waves behave much as we’d expect “normal” waves to.Īt the short- λ end of the spectrum lie the ultraviolet light ( λ on the order of a couple tens of to a couple hundred nanometers), the x-rays ( λ on the order of a few nanometers to a few hundredths of a nanometer), and the gamma rays ( λ on the order of hundredths of nanometers or less). At the long- λ end of the electromagnetic spectrum we find radio waves ( λ on the order of meters or more), microwaves ( λ on the order of centimeters to millimeters), thermal radiation ( λ on the order of tens of thousands of nanometers), and infrared light ( λ on the order of many hundreds of to thousands of nanometers). We’ll discuss things primarily in terms of λs here. They do this rather quickly: Light waves, and indeed all electromagnetic waves, travel in a vacuum at (unsurprisingly) the speed of light, about 3×10 8 m/s (roughly 186,000 miles per second!).Īll electromagnetic waves travel at the same speed in a vacuum, but they differ widely in wavelength ( λ), and therefore frequency ( f ), since the velocity of a wave is equal to the product of its wavelength and its frequency (see Everything You Need to Know About Oscillations & Waves for a fuller discussion of these concepts). It means electromagnetic waves can traverse the great expanse of nothingness between the sun and the earth. Here’s why that’s important: It means that an electromagnetic wave can propagate in a vacuum, no medium necessary. The changing magnetic field induces an electric field (see Everything You Need to Know About Magnetism), which in turn induces a magnetic field as it changes, which induces an electric field… and so on ad infinitum until the wave is absorbed or the energy it carries is otherwise transformed. It’s clear that understanding electromagnetic waves will help us understand how our world works, but what, exactly, are they? Let’s consider this question.Īn electromagnetic wave is a traveling wave composed of oscillating electric and magnetic fields. And electromagnetic waves shape modern life in many, many smaller-scale (but more immediate) ways: your cell phone, your wifi connection, your microwave, and medical imaging techniques such as x-ray and MRI are all brought to you courtesy of electromagnetic waves. This process makes life as we know it possible. Electromagnetic waves, like all waves, carry energy (see Everything You Need to Know About Oscillations & Waves) plants and photosynthetic algae make their way in the world by capturing a vanishingly small fraction of this energy as chemical energy. Almost all the energy on our home planet ultimately comes from the sun by way of electromagnetic waves (radioactive decays in the Earth’s crust also contribute some energy). ![]()
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