Visible irradiate is the part of the electromagnetic spectrum the our eyes can see:

It is just a small part of the complete spectrum, isn"t it?

Visible Spectrum

Visible Light: the wavelengths that are visible to most person eyes.

You are watching: Compared to yellow light, orange light has

The main colors, in order, go "Roy G Bv":Red Orange Yellow Green Blue Violet


As we see on this beautiful rainbow:




Light has actually a wavelength of about 380 nm to 750 nm, depending on color.

nm way nanometer, one billionth that a meter.

Example: red light has a wavelength of about 700 billionths that a meter (just less than one-millionth the a meter). Small!

THz method teraHertz, a sunshine cycles every second

So red light vibrates at around 400 million million cycles every second. Fast!

Higher frequency (with much shorter wavelength) has more energy:

Red light has actually lower frequency, much longer wavelength and also less energyBlue irradiate has higher frequency, shorter wavelength and an ext energy


Speed the Light

Light travel at practically 300,000,000 meters per second (to be exact: 299,792,458meters every second) in a vacuum.

That is 300 million meters every second, or:

3 × 108 m/s300,000 km/s186,000 miles per second

At that rate light travels:

1 meterin3.3 ns (3.3 billionths of a second)
Around the Earth"s equatorin134 multiple sclerosis (134 thousandths of a second)
From planet to Moonin1.3 s
Surface of sun to Earthinabout 8 minute

It is therefore fast, yet still takes around 8 minutes from the surface ar of the sun to the Earth.

The symbol for this rate is c:

c ≈ 300,000,000 m/s

Light have the right to Travel Slower

We really shouldn"t call it the rate of light, firstly due to the fact that it uses to the totality electromagnetic spectrum, and gravity waves, and more. Possibly we could contact it "Max Speed"!

But likewise because light only travels that speed in a vacuum! It have the right to travel slower ...

Wavelengthand Frequency are Linked

The Wavelength and Frequency are related:

Frequency = VelocityWavelength

Wavelength = VelocityFrequency

Assuming the light is ina vacuum, the velocity is the rate of light:3 × 108 m/s

Let"s try a straightforward example (in this situation not a wavelength the light):

Imagine a really long wavelength of 75,000 km


Frequency = 300,000 km/s75,000 km

= 4 /s

= 4 Hz

We have the right to fit 4 the those wavelengths in 300,000 km, so it vibrates 4 times in 1 second.

So the frequency is 4 Hz (4 per second)

Or, the other method around, if we understand it vibrates 4 time a second we can calculate that wavelength:

Wavelength = 300,000 km/s4 /s

= 75,000 km

Example: Blue light has a wavelength of about 480 nm (480 × 10-9 m)

So the frequency is:

Frequency = 3 × 108 m/s480 × 10-9 m

= 6.25 × 1014 /s

= 6.25 × 1014 Hz

Which is 625 TeraHertz

Light travel in right Lines

Light travels in a straight line until its hits something, or it"s course is adjusted by different densities, or through gravity.

Light native the sun streams throughout the road.The shadows likewise show that light travels in right lines.

This irradiate spreads out a little and is scattered by the atmosphere.

Laser beams making directly lines.



Light behaves together a wave, so the can:

scatter (bounce off in every directions),transmit (pass right through)or obtain absorbed


Light also behaves as packets that energy dubbed Photons.

We can measure a photon"s position and also momentum.Photons have no mass, however each photon has an quantity of energy based upon its frequency (number the vibrations per second)Each photon has a wavelength

So it is like a particle and likewise like a wave. This is called the "wave-particle duality".


Einstein wrote:

"It appears as despite we need to use occasionally the one theory and also sometimes the other, when at time we may use either."


Intensity is power every area, normally in watt per square meter:

Intensity = W/m2

Example: sun on a small 100 square meter house

About 150 come 300 watts of power are obtained from the sun per square meter.

Let"s pick the smaller number:

Intensity = 150 W/m2

How much Power is the over the entirety roof?

Power = 150 W/m2 × 100 m2

Power = 15,000 W

So a little house gets around 15 kilowatts top top it"s roof,which is several times an ext than a family members uses.

But that is just while the sun shines, and only about 20% deserve to be recorded by typical solar panels

But the is still too many of energy from the Sun.

Inverse Square

Inverse Square: when one value decreases together the square that the various other value.

Example: light and also distance

The further away we are from a light, the much less bright it is.


The brightness decreases together the square of the distance. Because the light is dispersing out in all directions:

the power twice as far away is spread out over 4 times the areathe power 3 time as far away is spread out over 9 times the areaetc


Light is normally cost-free to vibrate in any type of direction at best angles to its path.

But polarized irradiate vibrates in one plane only:

Light gets partly polarized once itbounces turn off surfaces like water or glass.

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Polarizing lenses have the right to block irradiate from that plane, to cut down on reflect light and make it easier to see right into water:

Without and with a polarizing lens

Fiber Optics

Light, and infrared, have the right to be sent out along fiber optic cables, carrying information coded right into the wavelength.

Fiber optic cables

The light continues to be inside since of a special building of refraction: when the refractive index is lower on the outside, and also the edge is not as well steep, the light beam has total internal reflection on the inside:

Light bounces off the walls inside the cable

Fiber optic cables room much much better than electrical wires:

Wires get much more "noise" (other signals that distort or interfere through the original) from power lines, TV, radio, lightning etc.Photons have actually no mass so have the right to swap between 0 and 1 quickly. Electrons have mass and are slow in comparisonGlass has actually much much less resistance to light 보다 copper does to electrical signals, so deserve to go much more without needing a boost

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Electromagnetic Spectrum Physics Index