Unvailing of the truth 1: go back

Optics : The physics concept behind many of the magic tricks is optics -- a science of light. We need light to see things. Our brain would analyze the informations light brought to our eyes and then tell us what we see. That is why we can't see anything in darkness and we can't see what is behind us unless we use a mirror to reflect the image to our eyes.

Color : We all know that a single ray could diverge, or split, into 7 colors as seen in a rainbow (red, orange, yellow, green, blue, indigo, and violet.) Although light travels in the same speed when in the same medium, each of them has different characters. However, all colors can be defined by three basic colors -- blue, red, and green.

We can see colors because our eyes have light and color-sensitive receptors called rods and cones. Their job is to detect the "relative" amount of red, blue, and green lights and their brightness. For example, if an object absorbs light and reflects mostly blue, then we see a blue object, and if the object reflects relatively equal amount of blue and red colors and aborbes mostly other color (yellow), then we see an purple object.

To test for the color combination, you can set the background color of your monitor screen. You will see then the background of your screen could be set with different amount of red, blue, and green. For example, set the background color to be blue = 0, red = 50 and green = 50, and we get a blackish green. Then without changing the settings of green and blue, we increase the setting of red color by 50 each time, and notice that the color changes from blackish green to dark brown and then eventually to bright orange. One can get all sorts of colors just by varing the combination of green, blue, and red color. If then increase the amount of green = 250 and red = 250 (blue still equals zero,) we obtain yellow.

Unvailing of the truth 2: go back

Fermat's Principle : What path does light take when traveling from one point to another? In 1657, Fermat proposed that light takes the path that requires the least time. We all know that with constant speed, the fastest way to travel is to take the shortest path. We also know that the shortest distance between 2 points is the straight line connecting these two points. Therefore, in the same medium, light travels in straight line from one point to another. When we see an object, we actually receive the information about that object brought by the light which is reflected directly and straightly from the object.
 
Unvailing of the truth 3: go back

Reflection : Just look into a mirror, and the image you see in the mirror is your reflection. Light travels in a straight path, but it bounces to another direction when the material it hits cannot be penetrated. This is also how when using a mirror, you can see what is behind you. Although the light coming from behind you cannot reach your eyes directly, if it hits a surface which would not absorb the light and would reflect it back to your eyes, you could still get the information about an object. That is why we use a mirror when we want to see something not within the range of our vision.

How is light reflected? If you did the activity given at the end of the Card Magic section, and use a string to connect the magician, the card, and the mirror, you will see that the incident angle of light (the angle at which the light hit the mirror from card) and the reflection angle (the angle at which the light was reflected to magician's eyes from the mirror) are equal.

Reflection
Diagram #1

Refraction : Have you ever stand in water and try to grab a shining coin at the bottom quickly but miss it? Or when you are taking a hot bath, have you try to put your hand below water, point your finger toward the surface of water, and see how short it looks from normal? Well, this is the work of light being refracted (or bend) when traveling from one medium into another. To make it simple, light bends when the density of the medium changes, and its velocity changes as well. It is just like walking in mud is much more difficult and slower then walking in the air.

However, our eyes do not know that light has been bent or refracted before it hits our eyes. So our brain would still analyses the informations about the object as if the light were traveling in a straignt line. Thus, the difference between the actual light path (the straight line) and the light path our brain imagined (the dotted line) cause the object looks closer.

Refraction
Diagram #2


Therefore, the coin at the bottom of water is actually farther down then it seems to be, and your toe looks shorter then it actually is.

Unvailing of the truth 4: go back

Mirrors : A mirror is a surface which is aluminized to block the light from going through. Basically speaking, the shiny surface reflects the light that hits it, and by changing the thickness of the aluminum foil applied to reflect light and by changing the curvature of the mirror surface, one can construct different types of mirrors for different purposes.

Concave Mirror :

Reflection
Photo #1

From the name, imagine you are walking into a cave of mirror. The diagram below shows you how a concave mirror looks like. To understand how a concave mirror works, we firstly recall what we learned in the "reflection" section. Remember that the principle of reflection does not change with the curvature of a mirror surface, so "the incident angle = the reflection angle" still applies to the concave mirror. Recall Diagram #1, just simply bend, or curve, the plane mirror so that the incident rays (red) are parallel to each other.

A concave mirror will have all incident light focus at a certain point and therefore, produce a real image of the object. A convex mirror is a plane mirror curved in the oppisite direction and has its focus behind the mirror and therefore, produce a virtual image.

Transparent Glass Mirror (Two-Way Mirror) : A two-way mirror is a transparent material coated with a thin layer of aluminum so that only a desired amount of light will be reflected. This is a two-way mirror because both sides of the glass can serve as a mirror. When one side of the glass is much darker then the other side, the mirror acts as a glass from the darker side and the glass acts as a mirror from the brighter side. It is because the light coming from the darker side is insignificant comparing with the amount of light in the brighter side so people at the brighter side basically see their own reflection and not what is behind the glass. This mirror is used in my magic box demostration so that when the light bulb hide behind the glass is off, the area behind the glass is darker and no one can see the light bulb, but when the light is on, the side behind the glass is brigher then the other, light transmitted from inside the box, and people can see the light bulb.

The transparent glass I used for my magic box has 37% reflection. It means that with 100 incident rays, 37 of them would be reflected and 63 would go through the glass to the other side.