Escape the Raindrops

-

 Ever wondered how a rainbow forms? Raindrops act like a prism and split the light into the colours of the visible spectrum. The splitting is called dispersion. The splitting is caused by refraction.


Ray diagram showing how sunlight is refracted and reflected in a raindrop



That's not the whole story though. After entering the raindrop, the light is reflected off the back surface. It then travels out of the front of the drop, refracting again at the boundary. If, when this light leaves the raindrop, it happens to travel to your eyes, you see the familiar bow in the sky. What this means is that nobody sees the same rainbow as you. A friend stood next to you sees the light that has been refracted in their direction.


double rainbow, promary rainbow, secondary rainbow, sr machanism



Ever heard of the famous double rainbow? They are formed when the light reflects twice inside the raindrop. Have you ever noticed that the colours in the second rainbow are reversed? The diagram above shows why.


Other affects you may notice when you see a good rainbow are supernumerary bows (green and magenta bows underneath the other bows. These are caused by a process called interference), Alexander's dark band (a dark region between the two bows) and that the area under the bows is very bright.



Do you want a challenge and to find out more about light? Click on the image below….




Popular posts from this blog

Escape The Ant Colony

-
Image
  Here's a really bad science joke that I've heard. Why don't ants get sick? Because they have little anty bodies.  I'll get my coat. That's not the only link between ants and disease prevention. I was listening to a podcast the other day where the discussion was about antibiotic resistance. This is a huge problem, which has lots of doctors and scientists are very worried. Antibiotic resistance is when antibiotics no longer kill bacteria. You can take the tablets, but they won't make you better. To understand why doctors are concerned we need to look back at what life was like before antibiotics.   In 1941 Police Constable Albert Alexander was injured in an air raid. A small cut near his mouth became infected and he was taken to hospital.  The infection got worse, and he developed sepsis, which is when your immune system overreacts to an infection and starts attacking your own organs. Most people who develop sepsis die. Doctors in 1941 were used to seeing people
Read more

Escape the Tamping Rod

-
Image
  The brain is the most complex structure we know, so studying and discovering how it works is complex. For many years scientists have had to rely on dissecting brains when they're dead (we hope), which means they're no longer working. Not an ideal way to discover how something works. Another strategy is to study what happens to a person when something goes wrong with their brain, which brings us to the unfortunate Phineas Gage. At approximately 4:30 on 13th September 1848, Gage was working at clearing rock for a new railway. He was preparing an explosive charge, using a long metal rod to pack the explosives into a hole drilled into the rock. A spark caused the charge to explode, propelling the rod up through his cheek and out through the top of his head. The rod was blown 25m away from the accident. Miraculously Gage survived this. Stories of his treatment following the accident are full of brain matter falling out of wounds and infections. The doctors could even see his '
Read more

Barcoding the Stars

-
Image
Looking up at the night sky, you will see dozens of stars. If you live in a very dark place, you may even see hundreds. The thing that people find difficult to grasp is just how far away these stars are. Our sun is 150 million km away from earth. If you could travel at the speed of light, which is as fastest you can go, it would take 8 minutes to get there. To get to the next nearest star at the speed of light, you would be travelling for 4 years (that's without toilet stops). Other objects are much further away. There are billions of galaxies outside of our Milky Way. Light from one of the nearest takes over 2 million years to reach earth. That is truly a galaxy far, far away. This is the Andromeda Galaxy, the farthest object you can see with the naked eye. We can't get to the stars to study them, so how do we find out how they work? The answer is light. We use telescopes to collect light from the stars and watch them move and change. Some telescopes detect light that we can&#
Read more