Electromagnetic waves

[Rachel Maddiee]

Energy increases as the electromagnetic wavelength decreases and the frequency increases. The energy of a wave is directly proportional to its frequency. A wave will transmit more energy per second if it has a higher frequency. Shorter wavelengths are more energetic than longer wavelengths.

Is this correct?

[studiot]

Yes it is correct, but you might like to use one of your sentences to say why these statements are true.

What is the relationship between frequency and wavelength?
You have mentioned electromagnetic waves, although your question simply says waves.
Does this make a difference?

[Carrock]

16 hours ago, Rachel Maddiee said:

Energy increases as the electromagnetic wavelength decreases and the frequency increases. The energy of a wave is directly proportional to its frequency. A wave will transmit more energy per second if it has a higher frequency. Shorter wavelengths are more energetic than longer wavelengths.

Is this correct?

See Studiot also for more clues.

I'm being picky, but there's a lack of information here. Maybe p.138 helps.

Your answer is correct only if you are referring to individual photons. Is 'wave' in the question intended to be synonymous with 'photon?'

It seems that a correct answer is 'not at all.'

e.g. a laser produces a 1Watt beam with wavelength 441.6nm. Its power is increased to 10W still at 441.6nm. How has the beam wavelength changed?

 

[swansont]

2 minutes ago, Carrock said:

See Studiot also for more clues.

I'm being picky, but there's a lack of information here. Maybe p.138 helps.

Your answer is correct only if you are referring to individual photons. Is 'wave' in the question intended to be synonymous with 'photon?'

It seems that a correct answer is 'not at all.'

e.g. a laser produces a 1Watt beam with wavelength 441.6nm. Its power is increased to 10W still at 441.6nm. How has the beam wavelength changed?

 

I was thinking about this; I agree. It's a poorly-worded question, because of the other variable the energy (or power) depends on.

[studiot]

31 minutes ago, Carrock said:

e.g. a laser produces a 1Watt beam with wavelength 441.6nm. Its power is increased to 10W still at 441.6nm. How has the beam wavelength changed?

Well spotted. +1

The energy can change without chnage of wavelength or frequency.

You don't need a laser for this.

Just turning up the volume on the radio will do it.
(This is a hint towards swansont's other variable)

 

So it boils down to what change was made first ?

Energy, frequency, wavelength, or what ?

Edited January 7, 2020 by studiot

[Rachel Maddiee]

Pg.138

[studiot]

What a mess of a question.

 

Well page 138 suggests we are talking about electromagnetic waves and the comment adjacent to Fig3 mentions swansont's other variable - amplitude.
In the text it also refers to the relationship between frequency and wavelength I mentioned.

 

Does the book say anywhere what the relationship between amplitude and energy is?
(there is a very important one)

 

After this you will know this substantially more than other less diligent students on your course.

Edited January 7, 2020 by studiot

[Rachel Maddiee]

Wavelength and frequency are inversely related.

I don’t really see anything about the amplitude in that information?

The speed of light is equal to the product of the wavelength and frequency 

[studiot]

Suppose you are standing on the beach.

Would you like to be hit by a large wave or a small one ?

A large wave has greater amplitude than a small one.

[Rachel Maddiee]

The amount of energy carried by a wave is related to the amplitude of the wave. A high energy wave is characterized by a high amplitude; a low energy wave is characterized by a low amplitude. ... 

 

But it does not ask about the relationship between amplitude and energy?

What exactly did I miss in my explanation?

[studiot]

14 minutes ago, Rachel Maddiee said:

The amount of energy carried by a wave is related to the amplitude of the wave. A high energy wave is characterized by a high amplitude; a low energy wave is characterized by a low amplitude. ... 

 

But it does not ask about the relationship between amplitude and energy?

What exactly did I miss in my explanation?

Yup, in fact the energy of a wave is proportional to the square of the amplitude.

 

https://www.physicsclassroom.com/class/waves/Lesson-2/Energy-Transport-and-the-Amplitude-of-a-Wave

 

 

You question says

Quote

The amount of energy it carried was increased

 

But it did not say how.

 

So you have two separate factors which can increase the energy

Changing  the amplitude

Changing the frequency

 

Your explanation should work the energy relationships backwards to explain how the energy was increased with each and therefore what the effect was on the frequency and wavelength.

[Rachel Maddiee]

So do I need to include that in my explanation?

[studiot]

Just now, Rachel Maddiee said:

So do I need to include that in my explanation?

 

I think we all here suggest you do.

[Rachel Maddiee]

   19 hours ago,  Rachel Maddiee said: 

Energy increases as the electromagnetic wavelength decreases and the frequency increases. The energy of a wave is directly proportional to its frequency. A wave will transmit more energy per second if it has a higher frequency. Shorter wavelengths are more energetic than longer wavelengths. The amount of energy carried by a wave is related to the amplitude of the wave.

i don’t need to include anything about photons or speed of light, do I?

[Carrock]

1 hour ago, studiot said:

What a mess of a question.

This is a perfect answer, but I doubt it would get any marks...

23 minutes ago, studiot said:

I think we all here suggest you do.

What you're writing is educationally valuable but I think OTT for what should have been a simple question.

 

Rachel:

You seem to have to have reverse engineered the question and realised the author meant 'photon' rather than 'wave.'

However you have unfortunately 'learned' that photon' and 'wave' are interchangeable, which needs to be unlearned ASAP. Wherever you learned about photons it was not from this question!

I'll break the letter of 'Homework Help' rules and give you a (slightly) corrected answer.

 

Quote

 

'Wave' in the question is a vague, undefined concept, and the effects of adding energy are therefor not predictable.

 

If 'photon' is substituted for 'wave' then the following are true:

Energy increases as the photon wavelength decreases and the frequency increases. The energy of a photon is directly proportional to its frequency. Shorter wavelength photons are more energetic than longer wavelength photons.

 

Saying in three different ways that frequency rises and wavelength falls, without repetition, is a challenge in itself...

 

9 minutes ago, Rachel Maddiee said:

i don’t need to include anything about photons or speed of light, do I?

I think you need to mention photons if you go beyond  "'Wave' in the question is a vague, undefined concept, and the effects of adding energy are therefor not predictable."

Edited January 7, 2020 by Carrock
Grammar

[Rachel Maddiee]

But photon is not in my reference page..

[Carrock]

"'Wave' in the question is a vague, undefined concept, and any effects on frequency or period of adding energy are therefor not predictable."

There's just no better answer without making assumptions which are not mentioned in the question or reference.

Surely your teacher will understand that the question is 'wrong' rather than the answer.

[Rachel Maddiee]

I think I’ll stick with “wave” since that’s how it defined in my book

[studiot]

7 minutes ago, Carrock said:

"'Wave' in the question is a vague, undefined concept, and any effects on frequency or period of adding energy are therefor not predictable."

There's just no better answer without making assumptions which are not mentioned in the question or reference.

Surely your teacher will understand that the question is 'wrong' rather than the answer.

Whilst I agree that the question is not clear, there is indeed an answer closer to what I understand the question to mean.

3 hours ago, Rachel Maddiee said:

  23 hours ago, Rachel Maddiee said:

   19 hours ago,  Rachel Maddiee said: 

Energy increases as the electromagnetic wavelength decreases and the frequency increases. The energy of a wave is directly proportional to its frequency. A wave will transmit more energy per second if it has a higher frequency. Shorter wavelengths are more energetic than longer wavelengths. The amount of energy carried by a wave is related to the amplitude of the wave.

i don’t need to include anything about photons or speed of light, do I?

No I would not mention photons and but you could mention the constant speed of light since it connects frequency and wavelength, both of which you are asked about.

But I also still say you need to reverse your thinking and statements.

Fig 3 says you can infer that change of frequency does not affect amplitude, so you can infer that there is no direct connection between amplitude and frequency.

In other words change of amplitude does not affect frequency.

But you know that the energy of a wave depends upon both frequency and amplitude, but independently of each other.

Page 138 refers to electromagnetic waves and shows light from a light source being split into different colours (frequencies).

So if you increased the power to that lightsource you will increase the light output - by increasing the amplitude of the lightwave.

Increasing the amplitude will increase the lightwave energy but will have no effect on the frequency or wavelength of the light.

But increasing the power to any real lightsource (with a spectrum as shown on page 138)  is likely to also change the frequency spectrum of the light.

This change will increase the relative amounts of higher frequency light.
This will also increase the relative amount of shorter wavelength light since the product of frequency and wavelength is the constant speed of light.

 

[Rachel Maddiee]

So I should definitely include lightwave energy?

[J.C.MacSwell]

5 hours ago, studiot said:

Suppose you are standing on the beach.

Would you like to be hit by a large wave or a small one ?

A large wave has greater amplitude than a small one.

The smaller ones give you the sunburn...