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# Hey boyos, someone help me understand this physics concept? watch

1. I'm homeschooled so it's not always simple to find explanations for things I don't get.
I've been struggling with 'Light' in physics for a week now (Edexcel P1, P3). The book I'm using doesn't clearly outline how to calculate refractive index and speed from refractive index. I'll try to break this down into questions:
1. How do you calculate speed from refractive index?
2. How do you calculate refractive index in the first place?
3. Probably the dumbest question but in formulae such as [sin C = 1/n], what does 'sin' mean? I know it's to do with angles but it never came up in math or physics lessons while I was in school - part of the reason I left was because they were understaffed and we were very behind in various subjects.
Any help would be much appreciated.
2. (Original post by aeroplanedriver)
I'm homeschooled

I know it's to do with angles but it never came up in math or physics lessons while I was in school
Surely you didn't stop studying maths when you left school? That is a serious mistake, especially as you seem to have stopped at quite an early stage of mathematical education - before GCSE level. You need to study maths if you study physics.

Even Wikipedia can explain sines to you.
3. (Original post by Good bloke)
Surely you didn't stop studying maths when you left school? That is a serious mistake, especially as you seem to have stopped at quite an early stage of mathematical education - before GCSE level. You need to study maths if you study physics.

Even Wikipedia can explain sines to you.
No, I'm still studying maths but it isn't something I've ever done yet - not even in school. I'm guessing it's trigonometry and obviously I will study that but this physics unit has come up first.
4. (Original post by aeroplanedriver)
No, I'm still studying maths but it isn't something I've ever done yet - not even in school. I'm guessing it's trigonometry and obviously I will study that but this physics unit has come up first.
Then I suggest you keep a better balance between the subjects, holding back physics topics until you have enough mathematical knowledge to cope.
5. (Original post by aeroplanedriver;68488452
1. How do you calculate speed from refractive index?
2. How do you calculate refractive index in the first place?
3. Probably the dumbest question but in formulae such as [sin C = 1/n
)

, what does 'sin' mean? .
1. n = c/v
2. Depends on what is known,
Snell's law is one method if the first medium is known such as air

3. sin means sine which is defined as " the ratio of the side opposite a given angle (in a right-angled triangle) to the hypotenuse"
6. (Original post by mphysical)
1. n = c/v
2. Depends on what is known,
Snell's law is one method if the first medium is known such as air

3. sin means sine which is defined as " the ratio of the side opposite a given angle (in a right-angled triangle) to the hypotenuse"
Thank you
7. (Original post by Good bloke)
Then I suggest you keep a better balance between the subjects, holding back physics topics until you have enough mathematical knowledge to cope.
Will do, thanks
8. (Original post by aeroplanedriver)
Will do, thanks
Take a look at this series of videos on trigonometry.

They will explain fully all you will need at GCSE level.

9. Thanks for replies. I did a bunch of trig stuff and it's actually really easy. Feel like an idiot now
10. I love the way this appeared in the list:

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