NTNUJAVA Virtual Physics Laboratory
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JDK1.0.2 simulations (1996-2001) => Optics => Topic started by: nin on March 12, 2007, 09:35:50 pm



Title: Mirage
Post by: nin on March 12, 2007, 09:35:50 pm
Sir, i'm nin from Malaysia. Can u explain the formation of mirage? it's quite confusing... And what is virtual object?? Here's a question : The Palomar Observatory Telescope has a parabolic mirror with a focal length of 80m.Calculate the magnification when a convex lens with a focal length of 5cm is used as the eyepiece. [ans:1600] how to do....? can ?? u explain? ??? ;D


Title: Re: Mirage
Post by: Fu-Kwun Hwang on March 13, 2007, 09:05:39 am
I do have a simulation for Mirage (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=207.0).
You can check it out and post your response there if you remains in doubt.

For virtual object, please check out Thin Lens combinations (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=47.0)
Right click the mouse button in the simulation region, it will become a two lens system.
Those gray lines represent vitrual object.
Actually, it is the image for the object when there is only one lens.
We use it to calculate the image when there is a second lens. (It is not a real object).


Title: Re: Mirage
Post by: nin on March 13, 2007, 02:39:24 pm
 :-[ i'm sorry, i still can't understand what is virtual object....about mirage, can u explain the mirage that we can see during a hot day and in the desert? i've seen the applet, but i dunno whether that parabolic shape represent a mirror. If it is a mirror, y it is  call a mirage not reflection??? and i've also seen the optigone website. The things inside the parabolic shape thing, is it placed inverted,so tht the image is upright?


Title: Re: Mirage
Post by: Fu-Kwun Hwang on March 13, 2007, 05:45:40 pm
In a hot day or in the dessert, because the temperature at different height are not the same.
So the air density is not the same which cause the refraction index of light to be different at different height.
If it cause light to bent, then you will see strange image.
(http://www.phy.ntnu.edu.tw/demolab/phpBB/pics/241_reflects.jpg)
Light emitted from the car move down then bent upward, and enter our eye.
It will appear to us that the light is coming from below the ground.
(Similar to a mirror was placed on the ground)!