AMASE: Rainbows

[Young woman standing in front of a world map.]

Princess Physics: Have you ever wondered how rainbows form?    

[Cut to Princess Physics, writing on a white board.]

[Upbeat music.]

[Cut back to Princess Physics in front of a world map.]

Princess Physics: Hi everyone! It's Princess Physics and today we're gonna learn about how rainbows are formed. They are everywhere you can see them when the Sun breaks through the clouds on a rainy day, you can see them in a collection of water droplets from a sprinkler in the summer and sometimes when you're lucky you can even see a double rainbow. All rainbows have one thing in common... You have to be at the right place at the right time to
see them. 

So, how do you rainbows form?

Why do we see all of the colors in the spectrum and why are the colors always in the same order? This amazing occurrence is a result of some simple properties of light waves such as
reflection, refraction and dispersion.

You've probably heard of reflection before. It's when a beam of light encounters a surface between two different mediums and instead of passing through the medium it reflects off of
the surface and comes back towards the way it was originally traveling.

[Cut to Princess Physics drawing a diagram of reflection on a white board.] 

[Music]

[Cut back to Princess Physics in front of a world map.]

Princess Physics: You see a reflection all the time in mirrors and windows and sometimes even water. 

The next property we'll talk about is refraction. Refraction happens when the path that a beam of light follows is bent when it passes between two mediums.

[Cut to Princess Physics drawing a diagram of refraction on a white board.]

[Music]

[Cut back to Princess Physics in front of a world map.]

Princess Physics: Now the last one, dispersion, is a little bit more complicated. Sunlight is sometimes referred to as white light because it's actually composed of all of the colours in a rainbow. 

[Cut to Princess Physics drawing a diagram of dispersion on a white board.]

Princess Physics: Each colour has a specific wavelength and each wavelength will refract at a different angle.

[Cut to animated diagram of white beam of light travelling toward a triangle shape, wavelengths separating into different colours as they exit the triangle.]

Princess Physics: This is called dispersion because the white light is dispersed into a spectrum of colours. 

[Cut back to Princess Physics in front of a world map.]

Princess Physics: The spectrum of colours is sometimes referred to as ROYGBIV which is an acronym meaning red, orange, yellow, green, blue, indigo and violet. So, because red has the highest wavelength it will be refracted the least amount. That's why red is always on the top of a rainbow. Violet on the other hand, has the lowest wavelength so what will be refracted the most. 

That order of colours is very well established and it's defined by their wavelengths so that's why they're always in the same order even when they're dispersed and reflected. 

[Cut to Princess Physics drawing a diagram of a water drop, being hit by sunlight on a white board.]

Princess Physics: So how do you rainbows form?

White light from the Sun approaches a raindrop. When the light passes from air into water the light will be refracted and dispersed into all of the colours on the spectrum and then when the dispersed colours reach the back of the raindrop they will all reflect and come back towards the Sun. This is why, when you see a rainbow usually the Sun is behind you. 

[Cut back to Princess Physics in front of a world map.]

Princess Physics: And this is how we get rainbows! Thanks for watching everyone and remember... never stop learning!

[Cut to animated triangle diagram.]

[Music]