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Information about this web site => Request for physics Simulations => Topic started by: leeyiren on January 10, 2010, 05:08:30 am



Title: Request for converging lens ray diagram with an adjustable screen
Post by: leeyiren on January 10, 2010, 05:08:30 am
There are many simulations on this site related to converging lens with an adjustable object.

Eg, http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1155.new;topicseen#new

To see the real image we need a screen. Yet i notice most simulations do not have an adjustable screen.

I would like to request a simulation of a converging lens ray diagram with an adjustable screen and object at different distance.

This suggestion has been posted on the thread (link above) but i would like to officially request for physics simulations on this board.

Lookang previously replied, "I agree with your suggestion. Let me do some research on ways to show the sharpness of the image on the screen."

This thread will assist me in keeping track of any updates in future. Pardon me if there are already applets out there. Pls direct me to it. Thx


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: Fu-Kwun Hwang on January 11, 2010, 02:15:46 pm
Most simulatuions only show the ray tracing of light paths for converging lens and indicate where the real/virtual image will be formed.
If a screen is located at the real image focus point, image will be seen.

If a screen is not located at the real image focus point:
 if it is close to the real image focus point, it will be a suposition of many images out of focus, and the intensity is also smaller.
 if it is too far away, no image will be formed.
Lookang was looking for ways to let image out of focus, and he is still working on it.
Please check out Re: how to model intensity and blurring of image in Ejs ? (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1391.msg5263#msg5263)

I would say the best way is to show a real experiment in front of the students, instead of a simulation.
May be what you need is an animation (not a real simulation) to illustrate the effect.

I will try to make one such simulation if I can figure out a way to present it.
Do you have any suggestion?


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: leeyiren on January 11, 2010, 06:27:17 pm
the following simulation maybe an inspiration?!?!
http://dl.dropbox.com/u/3579325/pencil%20and%20screen.jar

Actually the best way is to do an experiment. However i do not have the resources. I am currently self-studying physics. My understanding is basic and i cannot really visualise anything:-[ . I hope some pros can help newbies visualise without constructing an experiment, be it a simulation or animation or youtube video of the experiment. thx a lot.

PS: if not for the free simulations at this site i could not have got this far :-\ keep it up.


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: leeyiren on January 11, 2010, 06:32:32 pm
http://www.yenka.com/en/Yenka_Light_and_Sound/attachments/y-t2-1-1.gif

there is already a simulation out there. only its not free.... :'(


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: Fu-Kwun Hwang on January 11, 2010, 09:34:15 pm
For Pencil and Screen simulation, the original source is phet.colorado.edu/
However, it did not real show image for screen located at different place.
It only show the range of light source. And I do not think the intensity are being calculated.

For the image shown at  http://www.yenka.com/en/Yenka_Light_and_Sound/attachments/y-t2-1-1.gif
I am not sure is it a real simulation or is it just an animation?

It is not difficult to create a similar animation. But I am not sure is it a visual effect and/or is it base on  solid physics.
I do not think it is just a convolution of an image --- may be I am wrong.
It has to be a 3D simulation. And all the light paths need to be calculated to form the image.
It is a complicated task and we might really learn something new from the simulation.
The easiest way is to perform the simple experiment.

Quote
However i do not have the resources.
I think you can find the resources you need. It is not difficult to buy a lens. (magnify lens is available at many stores). You can use a candle as a light source. And you will understand more if you perform the experiment by yourself.
Simulation is good for experiments which are difficult perform or for some physics concept which need more visual effect or dynamic process which are not easily observed.

Simulation will not replace experiment. Simulation and experiment have it's own role.
For some cases, simulation is better than real experiment.
For some cases, real experiment is better than simulation.


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: leeyiren on January 11, 2010, 10:52:44 pm
Why is it so hard to form a real image of a toy soldier? Why do we always use candles and other luminous stuff?


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: Fu-Kwun Hwang on January 11, 2010, 11:12:38 pm
Because you need a strong light source to see the image.
Light from the object can go in all direction. Only those light which pass throught lens can form the image.
So the intensity become much weaker (not easy to observe).


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: leeyiren on January 11, 2010, 11:18:24 pm
i will be carrying out the experiment. What other objects you recommend? My concern is candle flames are dangerous and I may not be able to see the inversion as there is not must contrast in colour. The screen would be a wall. Any way to figure out the focal length. Should i do in a bright room? thx


Title: Re: Request for converging lens ray diagram with an adjustable screen
Post by: Fu-Kwun Hwang on January 12, 2010, 11:12:28 am
You can try it with a small light bulb even or flashlight. It will be better in a dark room instead of bright room if you use light bulb.
The screen can be a wall or paper. (a half transparent paper will be better, because you can look at the mage from both side).
Be careful about the candle flames.

Try to find a rectangle paper box (e.g. tissue paper box). Cut it into two equal size with a knife. And join them together so that you can change the width of the box (one side fit into inside of another half).
Cut a circle at one end so that you can put a lens there(you can glue it with 3M tape). Cut a rectangle area at another end and replace it with a larger half-transparent paper.
Put a light source in front of the lens, adjust the width of the box, and you can see the image form at the other side.
You might be able to look out window and see image from building next door at the other side (half-transparent paper) if you adjust the width of the box -- equal to the focus length of the convex lens.

It is similar to a pin hole experiment, but replace pine hole with a convex lens.