Home » Physics » Electromagnetism » Electromagnetic spectrum

Electromagnetic spectrum

Here is the Electromagnetic spectrum homework. open the file

The spectrum is the full range, of all wavelengths, of EM waves.
How much of this can we see with our eyes? (very little)
For blue and purple light, the width of these vibrating EM waves are, according to this diagram, about how wide? Roughly, according to this pic, the width of a bacteria cell.

Here is the EM spectrum.

Gamma rays Spectrum Properties NASA
NASA tour of the EM spectrum http://missionscience.nasa.gov/ems/index.html

All parts of the EM spectrum – radio, light, Wi-Fi, X-rays – are made of the same thing. The only thing different is their wavelength (or frequency.)

λ (wavelength) is the distance between successive crests

λ is the Greek letter lambda

f = frequency = number of times a wave’s peak passes/second



Gamma rays

Gamma rays have the smallest wavelength, and the most energy.

Their λ is about the width of an atomic nucleus.

They are generated by radioactive atoms, or nuclear explosions.

Tightly focused beams of gamma rays are used by doctors to kill cancerous cells.

Learn more about radiation and radioactivity here.

Here we see a nuclear reactor starting up. Nuclear fission releases gamma rays, and other forms of particles and energy.


λ  = width of an atom

Discovered in 1895 by Wilhelm Conrad Roentgen, a German scientist

We see below the first X-ray of his wife’s hand.

“The photograph electrified the general public and aroused great scientific interest in the new form of radiation. Roentgen called it “X” to indicate it was an unknown type of radiation. The name stuck, although (over Roentgen’s objections), many of his colleagues suggested calling them Roentgen rays.”

Roentgen 1st X-Ray

X-rays. Science.hq.nasa.gov

Ultraviolet (UV) rays

λ = width of a sugar molecule

They have shorter wavelengths than visible light

Invisible to the human eye

Small amounts of UV light help our bodies process vitamin D. Without this processing the chemical wouldn’t be in an active form.

Small amounts of UV light cause skin to tan (produce more melanin in the skin.)

Larger amounts of UV light cause sunburns. This damages the DNA in skin cells. Over time this DNA damage can lead to skin cancer.

Some insects see UV light, e.g. bees. They see flowers very differently than we do.

Left: Primrose in visible light; Right: Additional detail seen in UV light (false color)

Bjorn Roslett Primrose in visible and UV

Visible light

The only EM waves we can see.

Wavelengths of EM radiation that your eyes react to. All the colors of the rainbow – and every combination of them.

λ = about the width of a bacteria.

Shorter visible λ we perceive as blue.

Longer visible λ we perceive as red.

When our eyes see all the different visible λ together we perceive the result as “white.”


Prisms can break white light apart into a spectrum.

How? Each wavelength of light refracts by a different amount. This is called “dispersion.”


Infrared light

Infrared means “below red,” as infrared light has less energy than red light. We typically describe light energy in terms of wavelength, and as the energy of light decreases, its wavelength gets longer. Infrared light, having less energy than visible light, has a correspondingly longer wavelength. The infrared portion of the spectrum ranges in wavelength from 1 to 15 microns, or about 2 to 30 times longer wavelength (and 2-30 times less energy) than visible light.

Infrared light is invisible to the unaided eye, but can be felt as heat on one’s skin. Warm objects emit infrared light, and the hotter the object, the shorter the wavelength of IR light emitted. This IR “glow” enables rescue workers equipped with longwave IR sensors to locate a lost person in a deep forest in total darkness, for example. Infrared light can penetrate smoke and fog better than visible light, revealing objects that are normally obscured. It can also be used to detect the presence of excess heat or cold in a piece of machinery or a chemical reaction.

λ = width of a needle point

Infrared means “below red”. It has less energy than red light.

It can be felt as heat on our skin.

“Infrared light can penetrate smoke and fog better than visible light, revealing objects that are normally obscured. It can also be used to detect the presence of excess heat or cold in a piece of machinery or a chemical reaction.”

– from What is infra-red light? FLIR components

What can IR light show us. On the left we see, in visible light, a region in space where stars are forming.  Now look at the same region with IR light. This light penetrates the dust clouds, thus revealing more details.

IR light can penetrate thin layers of plastic.



Microwaves are a portion or “band” found at the higher frequency end of the radio spectrum, but they are commonly distinguished from radio waves because of the technologies used to access them. Different wavelengths of microwaves (grouped into “sub-bands”) provide different information to scientists. Medium-length (C-band) microwaves penetrate through clouds, dust, smoke, snow, and rain to reveal the Earth’s surface. L-band microwaves, like those used by a Global Positioning System (GPS) receiver in your car, can also penetrate the canopy cover of forests to measure the soil moisture of rain forests. Most communication satellites use C-, X-, and Ku-bands to send signals to a ground station.

Microwaves that penetrate haze, light rain and snow, clouds, and smoke are beneficial for satellite communication and studying the Earth from space. The SeaWinds instrument onboard the Quick Scatterometer (QuikSCAT) satellite uses radar pulses in the Ku-band of the microwave spectrum. This scatterometer measures changes in the energy of the microwave pulses and can determine speed and direction of wind near the ocean surface. The ability of microwaves to pass through clouds enables scientists to monitor conditions underneath a hurricane.

? http://missionscience.nasa.gov/ems/06_microwaves.html

— find source of this quote —

λ = width of butterfly wings

“Microwave ovens work by using microwave about 12 cm in length to force water and fat molecules in food to rotate. The interaction of these molecules undergoing forced rotation creates heat, and the food is cooked.”

Medium-length (C-band) microwaves penetrate clouds, dust, smoke, snow, and rain – Some weather satellite use them.

L-band microwaves are used by the Global Positioning System (GPS); signals are sent from GPS satellites in orbit, to the GPS in your car or phone.

“A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth’s surface, in this example at 45°N, changes with time.” {GPS Signals, Wikipedia}

GPS constellation satellites.gif

Some satellites use micowaves to determine windspeed & direction; very useful for studying hurricanes.


Studying rainfall in Hurricane Katrina (8/2005)

Lower frequency microwaves are used by engineers

Rebar is a steel reinforcing rod in concrete. Used in many buildings or highway overpasses.

If there is any rust on the rebar, since rust reflects less EM waves in comparison with sound metal, the microwave imaging method can distinguish between rebars with and without rust (or corrosion

Radio waves

λ     = hundreds to thousands of meters long

What creates radio waves?

* Wi-fi

* Bluetooth

* AM radio and FM radio

* TV (over-the-air television)

* Cellphone towers, as well as the cellphones themselves

* Stars (including our Sun)


How do we make AM radio waves?

We can use interference (a.k.a. superposition) to add two waves together to create a more complex wave. This lets us modulate the amplitude of the resulting wave. This is known as AM radio.
AM Radio waves Giancoli Physics

How do we make FM radio waves?

We may also add two waves together to modulate the frequency of the resulting EM wave. This is known as FM radio.
FM Radio waves Giancoli Physics


From the webcomic XKCD by Randall Patrick Munroe.

electromagnetic spectrum XKCD


EM spectrum in Astronomy

Multiwavelength Whirlpool Galaxy: Each image shows a narrow band of wavelengths of light and invisible radiation across the electromagnetic spectrum. The wavelength and energy of a photon relates to how fast electrons are accelerated. Low energy radiation comes from cool regions of molecular gas, and high energy radiation comes from hot spots where atoms are fully ionized. The combined images provide insight into the structure, temperature, and chemical composition of the Whirlpool Galaxy. The stars in the infrared image represent most of the mass of the galaxy, excluding dark matter, which can’t be seen. The optical image represents a slightly smaller amount of mass and the other three images represent only traces of mass in molecules (radio image) massive hot stars, (ultraviolet image) and hot plasma (x-ray image).

text from http://ecuip.lib.uchicago.edu/multiwavelength-astronomy/astrophysics/05.html

Multiwavelength whirlpool galaxy astronomy

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

6.MS-PS4-1. Use diagrams of a simple wave to explain that (a) a wave has a repeating pattern with a specific amplitude, frequency, and wavelength, and (b) the amplitude of a wave is related to the energy of the wave.

HS-PS4-1. Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling within various media. Recognize that electromagnetic waves can travel through empty space (without a medium) as compared to mechanical waves that require a medium.

HS-PS4-5. Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy. Clarification Statements:
• Emphasis is on qualitative information and descriptions.
• Examples of technological devices could include solar cells capturing light and
converting it to electricity, medical imaging, and communications technology.

Massachusetts Science and Technology/Engineering Curriculum Framework (2006)

6. Electromagnetic Radiation Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 6.1 Recognize that electromagnetic waves are transverse waves and travel at the speed of light through a vacuum. 6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green, blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum.

%d bloggers like this: