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A level physics, particles and radiation question

I came across a question that reads:
'A fluorescent tube is filled with mercury vapour at low pressure. After mercury atoms have been excited they emit photons
In which part of the electromagnetic spectrum are these photons?'

The answer is ultraviolet but I have no idea why, is there something in A level physics I am missing that would indicate why UV rays are emitted?
Reply 1
Original post by grhas98
I came across a question that reads:
'A fluorescent tube is filled with mercury vapour at low pressure. After mercury atoms have been excited they emit photons
In which part of the electromagnetic spectrum are these photons?'

The answer is ultraviolet but I have no idea why, is there something in A level physics I am missing that would indicate why UV rays are emitted?


I’m not sure what exam board you do but for AQA Physics that’s just part of the content, just something you have to learn :/
Original post by grhas98
I came across a question that reads:
'A fluorescent tube is filled with mercury vapour at low pressure. After mercury atoms have been excited they emit photons
In which part of the electromagnetic spectrum are these photons?'

The answer is ultraviolet but I have no idea why, is there something in A level physics I am missing that would indicate why UV rays are emitted?



My notes for AQA 7408. This is part of the content: 3.2.2.
"Ionisation and excitation; understanding of ionisation and excitation in the fluorescent tube."

Application: Fluorescent Tubes:
Constituents:
- has mercury vapour inside it at low pressure.
- is coated on the inside with phosphor.
- free electrons

A high voltage is then required to start the flow of current (the voltage accelerates the flow of electrons along the tube).

- Ionisation: The high-energy free electrons then ionise the mercury vapour - there are now more free electrons than previously.
- Excitation: The free electrons then excite electrons in the mercury atoms. After the electrons fall, they will release photons of frequency E/h, with a mixture of fixed frequencies due to the different levels the electrons have fallen to and from. The frequency of the photons released is categorised as UV radiation.
- Absorption & Excitation: The ultra-violet photons then collide with the phosphor coating on the inside of the tube. The electrons in the phosphor are now excited.
- The excited electrons then eventually move back to their ground state. When they do so, they release the excess energy in the form of photons. These photons have a frequency in the visible range.
Reply 3
Original post by speed_bird
My notes for AQA 7408. This is part of the content: 3.2.2.
"Ionisation and excitation; understanding of ionisation and excitation in the fluorescent tube."

Application: Fluorescent Tubes:
Constituents:
- has mercury vapour inside it at low pressure.
- is coated on the inside with phosphor.
- free electrons

A high voltage is then required to start the flow of current (the voltage accelerates the flow of electrons along the tube).

- Ionisation: The high-energy free electrons then ionise the mercury vapour - there are now more free electrons than previously.
- Excitation: The free electrons then excite electrons in the mercury atoms. After the electrons fall, they will release photons of frequency E/h, with a mixture of fixed frequencies due to the different levels the electrons have fallen to and from. The frequency of the photons released is categorised as UV radiation.
- Absorption & Excitation: The ultra-violet photons then collide with the phosphor coating on the inside of the tube. The electrons in the phosphor are now excited.
- The excited electrons then eventually move back to their ground state. When they do so, they release the excess energy in the form of photons. These photons have a frequency in the visible range.


Do you have the textbook for AQA physics? If so which page in the textbook is this mentioned?
Reply 4
Original post by grhas98
Do you have the textbook for AQA physics? If so which page in the textbook is this mentioned?

It’s page 37 :smile:
Reply 5
Original post by cata03
It’s page 37 :smile:


Thanks!

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