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Electromagnetic spectrum


Here is the Electromagnetic spectrum homework. open the file

B-field     magnetic field
E- field    electric field
EM            electromagnetic

Consider the EM spectrum:
from longest waves (far left) to shortest waves (far right)

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

What are these EM waves made of?

step 1: E- field

here we see an electric field radiating out of a circuit

Magnetic electric fields outside wire

step 2: B-field

A magnetic field around a bar magnet, made visible with iron filings.

Step 3:
Fact:  A changing E- field creates it’s own B-field
Fact:  But a changing B-field creates its own E- field 

Hmm… so E creates B, which creates E, which creates B, and so on… forever.

Yes, that’s right! Once you generate a E & B field like this, they travel through space forever, until they hit something.

Let’s see what this looks like:


Fields are at right-angles to each other

They travel through vacuum (empty space) at the speed of light

c  =  speed of light
c  =  3 x 108 m/s       =   186,282 miles/second

So all parts of the EM spectrum – radio, light, Wi-Fi, X-rays,
are all made of exactly the same thing! The only thing different among them? wavelength and frequency!

λ (wavelength) is the distance between successive crests

The symbol is the Greek letter lambda, λ


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


Gamma rays

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

Gamma rays have the smallest wavelengths and the most energy

Their λ    = width of an atomic nucleus

Generated by radioactive atoms, or nuclear explosions.

Can kill living cells. Tight beams of gamma rays can be used to kill cancerous cells

Learn more about radiation and radioactivity here.


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.”

Learn more about radiation and radioactivity here.

Roentgen 1st X-Ray


Ultraviolet (UV) rays

λ = width of a sugar molecule

Shorter wavelengths than visible light

Practically invisible to the human eye

Small amounts of UV light help our bodies process dehydrocholesterol (“Vitamin D”)
Without this processing the chemical wouldn’t be in an active form.

Small amounts also cause skin to tan (produce more melanin in the skin.)

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

Some insects see UV light, like bees. They would 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.

λ = about the width of a bacteria

Shorter visible λ we perceive as blue

Longer visible λ we perceive as red

All visible λ together we perceive as white


Prisms can break white light apart, through dispersion, into a spectrum.

Infrared light

λ = width of a needle point

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

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

“The image on the left shows an optical view of a star forming region. The same area is shown on the right in infrared radiation. Notice how the infrared observations penetrate the obscuring cloud to reveal many new details.”

IR light can penetrate thin layers of plastic.


λ = width of butterfly wings

“Microwave ovens work by using microwave about 12 centimeters 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

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.

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