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# Feedback Comments on Electromagnetic Waves

by Ron Kurtus

A total of 311 comments and questions have been sent in. They are listed according to date.

## List of next 10 letters

### Country

Refraction of Light Relationship between frequency and wavelength of light USA

Lasers How does the photoelectric effect work? South Africa

X-ray Generation Characteristic x-ray and k-shell production Rwandwa

Dispersion of Light What is the colour of green flowers in red light? Kenya

EM Waves What is the function of electromagnetic waves? Indonesia

EM Waves Why does wavelength matter in transmission of waves? UK

Doppler Effect Equations for Light I think your equations are incorrect USA

EM Waves Can you change the wavelength? Sweden

Dispersion of Light Meaning of wave-particle paradox? Nigeria

Dispersion of Light Separating white light into its spectrum Nigeria

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First 10 letters

## Relationship between frequency and wavelength of light

Topic: Refraction of Light

### Question

June 14, 2010

Please could you help. I dont understand how frequency can stay the same but the wavelength can be different . I thought the two were linked , so if you have higher frequency then you have shorter wavelength. how can the light wave be slower going through glass, but not the frequency be affected?

Im confused.
Thanks for any help

james - USA

19902

The relationship between frequency and wavelength is c = fw, where c is the speed of light, f is the frequency and w is the wavelength.

Frequency is the number waves per second that comes from the source. That number does not vary. However, when light passes through a material like glass, its speed slows down. If the speed is slower and the frequency is the same, then the wavelength will be shorter.

## How does the photoelectric effect work?

Topic: Lasers

### 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

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.

## Characteristic x-ray and k-shell production

Topic: X-ray Generation

### Question

May 27, 2010

but what differences between characteristic x-ray production and k-shell production?
looking forward
damascene

damascene - Rwandwa

19802

Characteristic x-rays are emitted from heavy elements when their electrons make transitions between the lower atomic energy levels. The x-rays produced by transitions are called K-alpha and K-beta x-rays.

Characteristic x-ray production and k-shell production are basically the same.

## What is the colour of green flowers in red light?

Topic: Dispersion of Light

### Question

May 10, 2010

what is the colour of green flowers in a red lit room?

Taura - Kenya

19695

A green object reflects green light and absorbs all other colors. If the plant is perfectly green, it will absorb the red light and appear to be black.

However, the plant may have a small amount of red in its pigment. If that was the case, it would be a very dark red.

## What is the function of electromagnetic waves?

Topic: EM Waves

### Question

May 9, 2010

what is the function of electromagnetic waves?

okta - Indonesia

19691

Radio waves, television waves, microwaves, visible light, ultraviolet and x-rays are all forms of electromagnetic waves.

## Why does wavelength matter in transmission of waves?

Topic: EM Waves

### Question

May 3, 2010

I have been studying electromagnetic waves for a while now and i have been very confused about how the length of the wave matters to what objects it can pass through?

Alex - UK

19661

While sound waves are compression waves, electromagnetic waves are transverse, similar the water waves, except in all directions.

Consider a water wave approaching a barrier that was less than the height of the wave. This would hinder the wave from passing the barrier. That is a good analogy or model of why electromagnetic waves are blocked by the separation of atoms in a material.

Another factor is that some materials have a crystalline structure that allows the waves to pass through. Very long waves, such as radio waves, simply go around everything.

There is no pat answer, because there are so many variables involved, but this should give you somewhat of an answer to your question.

## I think your equations are incorrect

Topic: Doppler Effect Equations for Light

### Question

May 2, 2010

Hey, I just wanted to let you guys know that the equation you are showing as the model for the blue shift/red shift is the classical model. It works for sound waves, but not for electromagnetic waves. You have to account for the special theory of relativity.

The doppler effect for light needs to be modeled with:

Fs- Source frequency
C - speed of light
V - velocity (either approaching the receiver or moving away)

Fr=[((C-v)/(C+V))^1/2)]*Fs

This is only for a receiver remaining still

But when v is positive the source is moving directly away from the reviver and fr is always less that fs: when v is negative, the source is moving directly toward the receiver and fr is greater that fs.

The effect is the same for sound the the quantitative relationship is different.

Anyway.... I'm just a student, so you should check it out yourself, but I was cruising the ole internet and noticed that.

Hope this helps

Make sure and check this out first b4 you publish anything, I'm no physics professor. But I do know that you modeled it using the same equation for sound Doppler effect, and light acts differently because it doesn't require a median for travel and well... light is crazy....
You know that
Light is a mad crazy concept. Duality still bothers us, so ya....
Anyway
I might be procrastinating
So I'm just gonna end this now.

Email me for any clarification of my rambles....

Joseph - USA

19653

Thanks for your feedback. It is good that you are alert and looking deeper into things.

It is true that the equations given in "Doppler Effect Equations for Light" lesson at: http://www.school-for-champions.com/science/light_doppler_equations.htm are for the the classical model. Note that I have a condition that c >> v (the speed of light is much greater than the velocity of the object). In such a case, the equations hold or are a sufficient approximation.

The equations work fine for the Doppler radar used by police and in weather prediction. In astronomical measurements, the relativistic equations start to become more accurate.

Right now, I don't have a section on relativity, but I plan to get one up soon, and that will have the Doppler equations, taking relativity into consideration.

## Can you change the wavelength?

Topic: EM Waves

### Question

April 22, 2010

Is it possible to convert a particular electromagnetic wave to another wave in the electromagnetic spectrum. for example, convert visible light wave to microwave, or infrared to microwave.

How is this possible.

Michaels - Sweden

19585

Using the Doppler effect, you can increase or decrease the wavelength according to the relative motion and direction of the source. However, the velocity must be fairly great to cause a significant change in wavelength.

For the equations, see:
http://www.school-for-champions.com/science/light_doppler_equations.htm

Topic: Dispersion of Light

### Question

April 21, 2010

what is the meaning of wave particle paradox

ahmed - Nigeria

19576

In most cases light behaves as a wave. But in some cases, like the photoelectric effect, it behaves like a particle.

Likewise, electrons are thought of as particles, but sometimes they behave like waves.

This duality of being a particle and a wave has been puzzling and could be called a paradox.

## Separating white light into its spectrum

Topic: Dispersion of Light

### Question

April 21, 2010

what differences can we get spetrum of white light and dispersion of white light

ahmed - Nigeria

19575

Using a glass prism, you can separate the colors of white light into its spectrum. This is caused by the dispersion of the light by the glass prism.

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