Saturday, January 9, 2010

Illusion ?

Kepada murid 5Um dan 5Ukm yang mengambil matapelajaran fizik, sila ikuti siri "light" . Maaf saya tiada masa untuk membuat ulangkaji bahagian tingkatan 4 dengan anda setakat ini, kami perlu menghabiskan syllabus tingkatan 5 sebelum percubaan pertama yang dijangka diadakan pada bulan ogos.
Imagine a coin on the bottom of a shallow pool of water. If you reach for the coin, you will miss it because the light rays from the coin are refracted at the water’s surface.

Consider a light ray that travels from an underwater object to your eye. The ray is refracted at the water surface and then reaches your eye. Your eye does not know Snell’s Law; it assumes light rays travel in straight lines. Your eye therefore sees the image of the at coin shallower location. This shallower location is known as the apparent depth.

The refractive index of a medium can also be expressed as
n = real depth/apparent depth
n = refractive index ( without unit)

Let pratice:

1. A coin is placed at the bottom of a 40 cm deep pond. The refractive index for water is 1.33. How deep does the coin appear to be?

2. A coin appears to be 7 cm deep in a colourless liquid. The depth of the liquid is 10.43 cm.
a. Determine the refractive index of the liquid.
b. Identify the liquid.

3. A coin is placed in a bowl of acetone (n = 1.36). The coin appears to be 10 cm deep. What is the depth of the acetone?

4. A dot is drawn on a piece of paper and a glass prism placed on the dot according to the diagram.
(a) Use the information supplied to determine the refractive index of glass.
(b) Draw a ray diagram to explain how the image of the dot is above where the dot really is.


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