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# OCR PHYSICS B G491~ 19th May 2015 AM ~ AS Physics watch

1. (Original post by Tomm1998)

9a) 1Mbyte*1000*3 = 3072. Remember 1Mbyte is actually 1.024 not exactly 1.
Now do 3072/3500 to get 0.878, which is <1Mbyte.

ii) This is all about estimating, which you need a rough idea based on events in your own life to make an accurate judgement. The first box is about pages per book, which from my experiance tends to be around 300 pages, the second box to fill in is words per line, which I would roughly say is 15. Now you use your estimates to find an answer. It states thar 1 byte = 1 character which there is 6 of per word. So 6*15*30*300 = 810,000 bytes of information. Remember this isnt the exact answer, the answer will depend on YOUR estimates. There tends to be a range of answers, so you should be good as long as your estimates are reasonable.

9b) Firstly, convert minutes to seconds so it doesnt throw you off later. And be careful with this question, it asks for the answer to be in BITS per second. We were dealing with bytes earlier, so 1 bytes = 8 bits. Now, we use the answer from part ai) which is the information per book. 0.878Mbytes * 10^6 to get it into bytes, then * 8 to get it into bits. This will equal 7,024,000 now we divide this by 60 to get bits per second. 7,024,000/60 = 117067. Keep it to low s.f. and use standard form for big numbers. I got 1.17*10^5 bits/s.

ii) f = v / λ so plug in the numbers, 3*10^8/0.36 = 8.3*10^8Hz

iii) not really sure on this one, I guess just look and see what the mark scheme says?

Hopefully I helped and explained things
Man you make it sound so easy! Thanks!
2. Euuuggghhh I'm getting really consistent B's on past papers but need an A... Does anyone know of any useful materials online on imaging?
3. (Original post by freya.98)
Euuuggghhh I'm getting really consistent B's on past papers but need an A... Does anyone know of any useful materials online on imaging?
Are you losing your marks on the imaging section? Also google, askwillonline g491, its a blog with revision for OCR B. I would link it but my phone is refusing to paste in the link
4. Does anyone have any good tips on improving timing? I always skip the questions I get stuck on then go back to them but theres always one or two I never get round to :\
5. (Original post by yeslordsugar)
Hi! It says in the spec for materials section we need to know "direct evidence of the size of particles and their spacing" Probably being stupid but what is this!?! Also what equations do we need to know for materials that aren't on the formula sheet? Thanks so much!

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I was not told about any equations that we need to know that aren't in the paper :O
6. (Original post by lyricalvibe)
How's everyone feeling for the exam ?
i regret picking physics
7. Do people think this year will be materials heavy or like last year?
8. (Original post by NedSunshine)
i regret picking physics
Hah, I'm sure you'll do fine You finished all the content?

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9. (Original post by Fandalf)
Do people think this year will be materials heavy or like last year?
i hope like last year as I'm resitting and hate the materials stuff
10. Imaging is where I'm losing most of them (other than silly mistakes ofc), thanks for the blog! Hopefully if I can get imaging together that should pull up my marks by 4-6, which should bring me to an A
11. does anyone know of any good sites for materials revision?
12. When using log2 (Vtotal/Vnoise) and the answer is a decimal e.g. 2.8 do you use the integer number of bits below or above? E.g. 2 or 3? I always believed it was below but last years paper it only allowed above? Sorry if this is obvious, I am very confused ahaha
13. (Original post by lauren_2)
When using log2 (Vtotal/Vnoise) and the answer is a decimal e.g. 2.8 do you use the integer number of bits below or above? E.g. 2 or 3? I always believed it was below but last years paper it only allowed above? Sorry if this is obvious, I am very confused ahaha
You use the number above. It has always been like that as that's the only way it works. Think about it if you need 130 alternatives that requires log2(130)=7.02 now although rounding down to 7 might seem plausible 2^7 gives 128 which is 2 alternatives shy of what we want. So 8 bits is the minimum number of bits which can produce 130 alternatives.
14. (Original post by Fandalf)
You use the number above. It has always been like that as that's the only way it works. Think about it if you need 130 alternatives that requires log2(130)=7.02 now although rounding down to 7 might seem plausible 2^7 gives 128 which is 2 alternatives shy of what we want. So 8 bits is the minimum number of bits which can produce 130 alternatives.
Okay that makes sense, thank you! I was getting confused because of questions such as this, where the answer was below.
15. (Original post by terrytomlinson)
does anyone know of any good sites for materials revision?
These 2 pdfs are pretty helpful for pretty much all the materials stuff.

16. How do I enter inverse sin(9.81/2) on a Casio calculator ? I keep on getting maths error when I press shift sin.
17. (Original post by TheGeneral95)
How do I enter inverse sin(9.81/2) on a Casio calculator ? I keep on getting maths error when I press shift sin.
Sin values are between -1 and 1 9.81/2 is > 1 so thats why you're getting the maths error. You've obviously done the wrong calculation I believe?
18. (Original post by lyricalvibe)
How's everyone feeling for the exam ?
Not Brilliant! Looking through the content for the first time now! :L
19. (Original post by lyricalvibe)
Hah, I'm sure you'll do fine You finished all the content?

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Hey, ive learnt the content over the year but what is an effective method for quickly going over everything on one day? Should i make flashcards and write notes? Im also doing past papers aswell.
20. (Original post by HennersPD)
I completely agree! After last years debacle of a paper I'm really worried for this year! Just hope they'll be kind and give us something nice!
In the examiners report for last years paper they admit that they messed up big time, and noted that the timing was way off. Im 99% sure this paper will not be anywhere near as hard

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