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Answers to Readers' Questions on Physical Science:

Lasers

The following 12 comments and questions have been sent in. They are listed according to date.

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How does the photoelectric effect work?

Question

May 28, 2010

I've been confused since I started studying about lasers because I actually started by studying the photoelectric effect. When light is shone to a metal, the electrons in that metal vibrate or move to higher energy states depending on the threshold frequency of the metal and the frequency of the light that is being illuminated to the metal. Does an electron move away from it's nucleus? If it doesn't, how do we get electrons moving in solar panels? If it does,under what conditions?

Khanyisani - South Africa

19807

Answer

Although we normally think of light as a waveform, in the photoelectric effect, light is thought of as a particle called a photon. This is part of the wave-particle duality of small particles.

The frequency of light determines the energy of the photon. When a photon hits an electron in a metal, the energy of the photon can be absorbed, causing the electron to move to a higher energy level.

However, if the frequency and energy of the photon is sufficient, it will knock the electron out of orbit, causing it to become a free electron in the metal. Free electrons are the stuff of an electric current.

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Doing a science project on laser light beams

Question

November 28, 2009

Hi
I am doing a science project on laser light beams and I was wondering how i would do a good project on a red laser beam going through different colored waters.

- USA

18754

Answer

All of the colors from white light shining though colored water are absorbed except for the color of the water. Depending on how concentrated the coloring is, most other colors will barely shine through. Thus, red will pass through red water but not very well through dark blue water. Since yellow water is not concentrated, some red will be absorbed and some will make it look orange.

Knowing this, you need to define what you are trying to achieve. You might try to determine what colored water transmits the laser beam the best and which one is the worst.

Ideally, you could use a light meter to measure the values. If you don't have a meter, you can shine the light through the container of colored water and have the light shine on a white piece of paper. Have a few friends grade each color from 1 to 10 in brightness. Then you can compare the results.

I hope this helps with your project.

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Do photons have a mass?

Question

September 1, 2006

What is a photon and does it have a mass? Is it possibile to attach a photon to any substance? Please reply soon?

- New Zealand

11810

Answer

Although light is considered an electromagnetic wave, there are certain times it acts like a particle. In fact, light can be considered a waveform of photon particles. Photons are particles of light. For many years, scientists said that photons have no mass, but they recently found they do have a very small mass. The momentum of photons (mass x velocity) is used to push solar sails used in spacecraft.

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Laser beam shifting with time

Question

February 14, 2006

We are using good quality laser beams for proximity switching. We are facing very strange problem. On longer distance of over 15meters, we are unable to hold the beam on one single point of 4-5mm. Beam shifts its position in 5-6 hours and is totally out of our sensor (LDR). We have tried various types of mountings which are highly stable (rock-tight). So we are confused as what could be the reason of beam shifting its own position in 5-6 hours.

Now we feel that laser source is the culprit. Is our understanding correct ? Does the laser source (ruby rod) changes its position due to heat etc. Even a fractional micron movement at source, will result in over 10mm movement of laser beam at LDR which is placed at 25meters distance. Please help urgently.

regards,

Suresh - India

10077

Answer

It does seem that expansion due to a change in temperature is causing your shift, especially if it happens over a period of time.

Is your room temperature-controlled? If the room temperature changes, that could cause expansion in a variety of elements and could be visible in misalignment.

With a distance of 15 meters, I assume you are not using something like a granite optical bench. Note that metal rails could easily expand with temperature.

To reduce any possible expansion around your ruby laser, you might try a heat sink to reduce any heat buildup that could cause the problem.

I hope these ideas help.

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Wants to do a project with lasers

Question

February 7, 2006

My name is Nathaniel and I am in third grade. I would like to do something about lasers for my science fair project. I was thinking, "How a laser works?' I have been unsuccessful at finding material on lasers at a kids level. Do you have any suggestions for internet sights at my level (third grade) that would help me learn about lasers. My parents purchased a cheap laser pointer and I have laser tag game (but that it involves gun like that probably won't be acceptable at a school function. I also thought about purchasing the spy gear laser trip wire to do the project. Do you have any ideas what I might do? Some other ideas we thought about was lasers and CD/ DVD players and how they read the CD/ DVD? My parents aren't sure if this over my head.

Nathaniel - USA

9983

Answer

You really want to have some sort of demonstration with a laser instead of trying to explain how it works.

Lasers have some interesting properties. One is that if you shine a laser light on a piece of paper the spot will have a "speckle effect". Even the inexpensive pointer lasers should do that. You could show how it may change with different types and colors of paper.

Also lasers are just one color. What would happen if you shined laser light through different colored water? How much would shine through? What color would the light be?

One thing is to be very careful of laser light. Never look into the laser. Always do your testing by shining on some paper.

Best wishes in your project.

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Is it possible to live on the milky way?

Question

December 5, 2005

how does a light's speed can be measured? and it is posible to live on the milky way and can you make a electrons stay in one place with out trapping it?how does lazer work?

youngsoo - USA

9264

Answer

See our lesson on the speed of light at:
http://www.school-for-champions.com/science/lightspeed.htm

We are a planet in the Milky Way. There may be other planets that sustain life in the Milky Way.

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Do you have any ideas for a science project?

Question

November 7, 2005

Do you have any ideas for a science fair project that has to do with electromagnetic spectrum?

Angie - USA

8847

Answer

The electromagnetic spectrum consists of all the energy from the long radio waves to visible light to the very short x-rays. You want to pin things down to something more specific.

One idea is to work with the visible spectrum. If you can get a prism, you can shine light through it to show a rainbow effect of all the colors. Use a slit or point of light. You can also use sunlight to show the spectrum. Then you can compare the colors that come from various sources of light.

That may be an idea for a project.

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Wants to use green laser in scienc fair

Question

August 21, 2005

Hi, I need help with coming up with a Science Fair Project. I love green lasers, but I need some ideas on a project. I have won the science fair every year and I can't loose this year.

- USA

7839

Answer

A green laser can produce some cool effects. See:
http://www.thinkgeek.com/gadgets/lights/5a47/action/ to see some effects.

But there are two problems. One is that a green laser is not cheap. You can get red laser pointers that are much less expensive. The second problem is that although the effects are cool... so what? Can you win a contest just with something cool?

One thing to do is to show that advantage of using a green laser over a red laser for certain tasks. Since the green laser has a shorter wavelength, it may have advantages where a sharp focus is required. Also, you might show how combining green and red, you can create different colors or effects. Finally, you can try to show some special use of a green laser. Like, would it help plants grow?

I hope these ideas help. Best wishes in your science fair project.

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Can moving lasers create a picture?

Question

March 18, 2005

If an aray of green lasers is set up, on a circular ring, and spun at about 20 mph. can a picture from a digital projector be visible on the screen created ?

Richard - USA

6382

Answer

I'm not sure how you plan to project the pictures. You aren't thinking of a hologram are you? Taht works in a different manner.

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Is laser light is in the electromagnetic spectrum?

Question

January 18, 2005

Is the laser light is in the electromagnetic spectrum? What is the frequency? and What is the source of such a light?

Prabhu - India

5651

Answer

All light is in the electromagnetic spectrum. Lasers come in many colors, including infra-red and x-rays. They are generated by simulating the orbits in the material's atoms.

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