Electromagnetic Spectrum

Physics 1, Group 6, Rosal 2015

James Clerk Maxwell

With the equations he formulated on electromagnetic induction, he found that these equations had a speed of ~3.00 x 108 m/s w/c is equal to the speed of light

Discovered the nature of light (as electromagnetic waves)

Light wave as a transverse wave

Electromagnetic Radiation

Made of electric and magnetic fields vibrating, acc to wave theory, at right angles to one another and moving through space at the speed of light

Form of ENERGY that can travel through empty space

Classified across the spectrum by its wavelength

A transverse wave consisting of oscillating electric and magnetic fields

Electromagnetic Spectrum

All EM waves travel at the same speed in a vacuum, they differ from one another in their frequency & wavelength

Classification of EM waves according to frequency

Light is simple EM waves in this range of frequencies

Ex. Accelerating electric charge -> radiate in electric and magnetic fields

Radio waves Examples: radio stations, stars, aircraft and

shipping bands, TV and fm radio, astronomical bodies, lightning, can transmit info

Low wavelength, low frequency, low energy

Microwaves Microwaves in space are used by astronomers to

learn about the structure of nearby galaxies, and our own Milky Way!

Can penetrate through smoke, haze, clouds, and even light rain

Ex. Microwaves radar, transmit data, satellite imagery

Infrared Our skin emits infrared light, which is why we can

be seen in the dark by someone using night vision goggles. In space, IR light maps the dust between stars.

Even that we can not see or hear infrared, we can feel it at our skin temperature sensors.

Visible spectrum

Color Frequency Wavelength

violet 668–789 THz 380–450 nm

blue 606–668 THz 450–495 nm

green 526–606 THz 495–570 nm

yellow 508–526 THz 570–590 nm

orange 484–508 THz 590–620 nm

red 400–484 THz 620–750 nm

Visible Spectrum

Portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. 

corresponds to a band in the vicinity of 400–790 THz.

Reflects light off objects from any light source

Visible sunlight passes through the earth’s atmosphere and reflects off objects allowing us to see them

Why does a CD reflect rainbow colors?

Like water drops in falling rain, the CD separates white light into all the colors that make it up. The colors you see reflecting from a CD are interference colors, like the shifting colors you see on a soap bubble or an oil slick.

You can think of light as as being made up of waves-like the waves in the ocean. When light waves reflect off the ridges on your CD, they overlap and interfere with each other. Sometimes the waves add together, making certain colors brighter, and sometimes they cancel each other, taking certain colors away.

Why does a CD reflect rainbow colors?

On a CD, the surface is mirrored so the rainbow colors are much more intense.

the angle controls the path difference.

Ultraviolet Ex. Sun, stars and other “hot objects in

space emit UV radiation, “ultraviolet” because its frequency is just a bit higher than visible violet light, in gadgets, black light lamps

10 nm- 400 nm

X-Ray Naturally emitted by space objects like neutron stars, black

holes, binary stars, remnants of super nova, stars, comets, and even our own sun

X-ray images are produced when they are absorbed by what they strike and, leaving shadows on the film that imprints in an image

3nm – 0.3 nm

Gamma Rays Smallest wavelength

Ex. Nuclear power plants, big particle accelerators, stars, radiotherapy- used to kill cancer cells (gamma knife), kills microorganisms in food through irradiation, sterilizing medical equipment

Biggest gamma ray generator: naturally produced in the hottest regions of the universe

Light Comparison (f and λ)

LIGHT COMPARISONName Wavelength Frequency (Hz)Gamma Ray Less than 0.02 nm More than 15 EHzX-Ray 0.01 nm – 10 nm 30 EHz – 30 PHzUltraviolet 10 nm – 400 nm 30 PHz – 760 THzVisible 390 nm – 750 nm 770 THz – 400 THzInfrared 750 nm – 1mm 400 THz – 300 GHzMicrowave 1 mm – 1 m 300 GHz – 300 MHz

Radiowaves 1 mm – 100, 000 km

300 GHz – 3 Hz