Does red light have a longer wavelength than blue

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

Table of Contents Show

Light Can Travel Slower
Wavelength and Frequency are Linked
Imagine a very long wavelength of 75,000 km
Example: Blue light has a wavelength of about 480 nm (480 × 10-9 m)
Light Travels in Straight Lines
Example: Sun on a small 100 square meter house
Inverse Square
Example: light and distance
Polarization
Fiber Optics
Is the wavelength of red light longer than blue?
Does red light have the longest wavelength?
Why does red have a longer wavelength?
Which has a higher frequency red or blue light?

That is 300 million meters every second, or:

3 × 108 m/s
300,000 km/s
186,000 miles per second

At that speed light travels:

Distance Time1 meterin3.3 ns (3.3 billionths of a second)Around the Earth's equatorin134 ms (134 thousandths of a second)From Earth to Moonin1.3 sSurface of Sun to Earthinabout 8 minutes

It is so fast, but still takes about 8 minutes from the surface of the Sun to the Earth.

The symbol for this speed is c:

c ≈ 300,000,000 m/s

Light Can Travel Slower

We really shouldn't call it the speed of light, firstly because it applies to the whole electromagnetic spectrum, and gravity waves, and more. Maybe we could call it "Max Speed"!

But also because light only travels that speed in a vacuum! It can travel slower ...

MediumSpeed
million m/sVacuum299.8Air299.7Ice228Water225Ethanol220Glass205Olive oil204Diamond123

Wavelength and Frequency are Linked

The Wavelength and Frequency are related:

Frequency = Velocity Wavelength

Wavelength = Velocity Frequency

Assuming the light is in a vacuum, the velocity is the speed of light: 3 × 108 m/s

Let's try a simple example (in this case not a wavelength of light):

Imagine a very long wavelength of 75,000 km

Frequency = 300,000 km/s 75,000 km

= 4 /s

= 4 Hz

We can fit 4 of 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 way around, if we know it vibrates 4 times a second we can calculate its wavelength:

Wavelength = 300,000 km/s 4 /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/s 480 × 10-9 m

= 6.25 × 1014 /s

= 6.25 × 1014 Hz

Which is 625 TeraHertz

Light Travels in Straight Lines

Light travels in a straight line until its hits something, or it's path is changed by different densities, or by gravity.

Light from the Sun streams across the road.
The shadows also show that light travels in straight lines.

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

Laser beams making straight lines.

Wave

Light behaves as a wave, so it can:

reflect (bounce off),
scatter (bounce off in all directions),
refract (change speed and direction)
diffract (spread out past an opening)
transmit (pass straight through)
or get absorbed

Photons

Light also behaves as packets of energy called Photons.

We can measure a photon's position and momentum.
Photons have no mass, but each photon has an amount of energy based on its frequency (number of vibrations per second)
Each photon has a wavelength

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

Einstein wrote:

"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either."

Intensity

Intensity is power per area, usually in Watts per square meter:

Intensity = W/m2

Example: Sun on a small 100 square meter house

About 150 to 300 watts of energy are received from the Sun per square meter.

Let's choose the smaller number:

Intensity = 150 W/m2

How much Power is that over the whole roof?

Power = 150 W/m2 × 100 m2

Power = 15,000 W

So a small house gets about 15 kilowatts on it's roof, which is several times more than a household uses.

But that is only while the Sun shines, and only about 20% can be captured by typical solar panels

But that is still lots of energy from the Sun.

Inverse Square

Inverse Square: when one value decreases as the square of the other value.

Example: light and distance

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

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

the energy twice as far away is spread over 4 times the area
the energy 3 times as far away is spread over 9 times the area
etc

Polarization

Light is normally free to vibrate in any direction at right angles to its path.

But polarized light vibrates in one plane only:

Light gets partly polarized when it
bounces off surfaces like water or glass.

Polarizing lenses can block light from that plane, to cut down on reflected light and make it easier to see into water:

Without and with a polarizing lens

Fiber Optics

Light, and infrared, can be sent along fiber optic cables, carrying information coded into the wavelength.

Fiber optic cables

The light stays inside because of a special property of refraction: when the refractive index is lower on the outside, and the angle is not too steep, the light beam has total internal reflection on the inside:

Is the wavelength of red light longer than blue?

Blue light has a short wavelength; red light a longer wavelength. The sky looks blue because blue light is scattered far more than red light, owing to the shorter wavelength of blue light.

Does red light have the longest wavelength?

As the full spectrum of visible light travels through a prism, the wavelengths separate into the colors of the rainbow because each color is a different wavelength. Violet has the shortest wavelength, at around 380 nanometers, and red has the longest wavelength, at around 700 nanometers.

Why does red have a longer wavelength?

Why does red light have the maximum wavelength in a spectrum irrespective of having the maximum wavelength? It has the longest wavelength because it has the lowest energy.