# Oxford PAT 2015, Question 20

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## 6 thoughts on “Oxford PAT 2015, Question 20”

1. KY says:

I think for question C the answer should be 7 because only when the level falls to level 2 will produce observable light, which means only 10 to 3 can produce observable light. Thus the answer should be 7

1. Well, yes and no. Yes, as it turns out the only emissions of hydrogen visible to a human eye are when the lower energy level is 2. But no, physics the word “observed” does not just mean “observed by the naked eye” — it really means “detected (using any suitable apparatus)”. So, while most of the lines are in the UV or IR parts of the spectrum, they can still be detected using some sensors and so they can all be observed.

In the exam, unless a question specifically refers to the human senses in some way, you should assume that ‘observable” means “could be detected by some sensor system”

2. 20)c) says:

Thanks so much for the website it’s really useful!

Please could you explain your answer to part c? Sigma notations don’t come naturally to me

1. At energy level 10, we can generate 9 emission lines, corresponding to the photons emitted when we drop from 10 to 9, 10 to 8, 10 to 7, and so on down to 10 to 1. At energy level 9 we can generate 8 emission lines, corresponding to the photons emitted when we drop from 9 to 8, 9 to 7, 9 to 6, and so on down to 9 to 1.

In general, at energy level n we generate (n-1) emission lines. So the total number of emission lines is 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9, corresponding to the lines generated by energy levels 2, 3, 4, 5, 6, 7, 8 and 9 respectively.

The notation Σn, where 1 ≤ n ≤ 9, just means 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9.

3. Hi, this topic isn’t really going to be covered for my A Levels until November, so do you have any useful links where I can learn about quantum mechanics(if this is that topic)?
Thankyou.

1. To answer this question you need to know that the energy E of a photon is related to its frequency f by the equation E = hf where h is the Planck constant that the question refers to. The only bit of the syllabus that covers this is “atomic structure”, which is a bit cryptic. You could try looking at this site: http://www.bbc.co.uk/education/topics/znv39j6, especially the sections on wave particle duality and spectra.