[IR] Double Rainbow All the Way

Rainbows are a phenomenon that has been widely recognized as a beautiful natural occurrence throughout the stone age and now we understand the physics of the rainbow.
A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicolored arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.
In a so-called "primary rainbow" (the lowest, and also normally the brightest rainbow) the arc of a rainbow shows red on the outer (or upper) part of the arc, and violet on the inner section. This rainbow is caused by light being refracted then reflected once in droplets of water. 
It is impossible for an observer to maneuver to see any rainbow from water droplets at any angle other than the customary one (which is 42 degrees from the direction opposite the Sun)

The light is first refracted entering the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40–42°. The angle is independent of the size of the drop, but does depend on its refractive index. 

DOUBLE RAINBOW!!!

Although most people will not notice it because they are not actively looking for it, a dim secondary rainbow is often present outside the primary bow. Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky. A very dim tertiary rainbow, caused by a triple reflection of sunlight inside the raindrops, has been seen on rare occasions.

Supernumerary rainbow

A supernumerary rainbow—also known as a stacker rainbow—is an infrequent phenomenon, consisting of several faint rainbows on the inner side of the primary rainbow, and very rarely also outside the secondary rainbow. Supernumerary rainbows are slightly detached and have pastel colour bands that do not fit the usual pattern.

Reflected rainbow

When a rainbow appears above a body of water, two complementary mirror bows may be seen below and above the horizon, originating from different light paths. Their names are slightly different. A reflected rainbow will appear as a mirror image in the water surface below the horizon, if the surface is quiet. The sunlight is first deflected by the raindrops, and then reflected off the body of water, before reaching the observer. The reflected rainbow is frequently visible, at least partially, even in small puddles.

[IR] Plasmas

Plasmas are a lot like gases, but the atoms are different, because they are made up of free electrons and ions of an element such as neon (Ne). You don't find naturally occurring plasmas too often when you walk around. They aren't things that happen regularly on Earth. If you have ever heard of the Northern Lights or ball lightning, you might know that those are types of plasmas.

Aurora. Also Known As the Northern Lights

Ball Lightning

It takes a very special environment to keep plasmas going. They are different and unique from the other states of matter. Plasma is different from a gas, because it is made up of groups of positively and negatively charged particles. In neon gas, the electrons are all bound to the nucleus. In neon plasma, the electrons are free to move around the system.


While natural plasmas aren't found around you that often, man-made plasmas are everywhere. Think about fluorescent light bulbs. They are not like regular light bulbs. Inside the long tube is a gas. Electricity flows through the tube when the light is turned on. The electricity acts as an energy source and charges up the gas. This charging and exciting of the atoms creates glowing plasma inside the bulb. The electricity helps to strip the gas molecules of their electrons.

Fluorescent lights

Another example of plasma is a neon sign. Just like a fluorescent lights, neon signs are glass tubes filled with gas. When the light is turned on, the electricity flows through the tube. The electricity charges the gas and creates plasma inside of the tube. The plasma glows a special color depending on what kind of gas is inside. Inert gases are usually used in signs to create different colors. Noble gases such as helium (He), Neon (Ne), Argon (Ar), and Xenon (Xe) are all used in signs.

You also see plasma when you look at stars.

Sigh.... We won't even be able to see 1/10 of the stars here in Singapore

Stars are big balls of gases at really high temperatures.

How I interpret "Big ball of gas" ;) HAHA.

The high temperatures charge up the atoms and create plasma. Stars are a good example of how the temperature of plasmas can be very different.
Fluorescent lights are cold compared to really hot stars. However, they are still both forms of plasma, even with the different physical characteristics.

[IR] Solid or Liquid

This is an experiment Daryl and I did quite sometime ago, it is about non-newtonian fluids.

Things needed for the experiment.
1. A basin
2. Some water
3. A mixing spoon
4. Corn flour
5. Scissors
6. Measuring cup

Steps
1. Measure about 400 ml of water and pour it into the basin.
2. Open the packet of flour using the scissors.
3. Measure about 400g of corn flour with the measuring cup.
4. Pour the 400g of corn flour into the basin of water.
5. Mix flour with water using your hands.
6. Knead the mixture till it is settled.
7. It should look like melted cheese. Yum... : p
See the resemblance???

Now for the Fun Part!!!

Hit the mixture with force.
You should observe...
It feels hard like a solid, but you can clearly see ripples forming from where you hit the mixture but it does not splash out! You should also observe that it seems impossible to penetrate.

Whereas...
If you gently lay your hand on the mixture, your hand should sink through the mixture. And the mixture would gently flow and fill the spaces in the basin!

Try to...
"Tear" the mixture, you should find that you are able to somewhat "pull" and "rip" the mixture apart like a solid but it gently flows back like a liquid!

"Squeeze" the mixture, you should find that instead of flowing out like a liquid, it suddenly becomes hard and you can feel its shape, like a solid. It should feel like plasticine.

To the molecular level...
The 'Super Starch' is just a liquid with corn flour floating in it, but when you hit it with force, the water molecules are forced into the middle of each grain of flour and it becomes a solid!

In everyday life...
If you run over the wet sand, you should find that it is firm, but, if you stroll along, your feet will sink into the sand.

Why does this mixture have such an interesting property?
Some fluids (liquids & gases) mixtures have two forms.
A liquid can become a solid. This is called "isotropy"

The opposite of isotropy is "thixotropy".
Thixotropy is a liquid mixture becoming "more liquid" (more runny).
An example of thixotropy is when you need to get ketchup out of the bottle, so you had hit the base of the bottle. The act of hitting it at the base makes the ketchup "more liquid" so it can flow out easier.

This is a prezi we also created:

http://www.youtube.com/watch?v=_03fAC0pZ0Q