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# Edexcel Physics Unit 3 9th May Watch

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1. (Original post by Relaxedexams)
10^-28

I suppose its the line of best fit then.

So 1 mark each for line of best fit, wrong gradient, not changing units to SI by multiplying by 10^6, and wrong final planck constant? I also put unit as Js without converting to SI. Will I get docked a mark for that too?
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Wrong gradient is carried over from wrong line of best fit. If your gradient calculation was correct for the line of best fit you drew, you'll probably only lose one mark total for both of those.

Wrong final planck constant is also carried over, since it's carried over from the wrong gradient which was carried over from the wrong line of best fit (one simple error can lead to so many things! ). I'm not 100% sure how they'll mark this, you'll either lose 0 or 1 mark.

Not multiplying by 106 but still putting unit as Js is probably considered one mistake, so deduct 1 mark for that.

So overall 8 or 9 out of 11.
2. (Original post by Relaxedexams)
I got 3.63! Which is much closer to your value than the others at my school. Most of them got 5!

I suppose its because they didn't cut through the origin, so their gradient was larger, leading to a higher planck constant.

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I'm definitely not promoting my answer as the correct one though. To be honest I'd be more confident in my answer if I'd got 5 like your friends, since it's closer to the real value. I may be good at maths, but my graph drawing is terrible, so your friends may very well have gotten a "better" answer than me.
3. (Original post by justinawe)
I'm definitely not promoting my answer as the correct one though. To be honest I'd be more confident in my answer if I'd got 5 like your friends, since it's closer to the real value. I may be good at maths, but my graph drawing is terrible, so your friends may very well have gotten a "better" answer than me.
Hey guys
I got a value of 5.2*10^-34 Js
i looked at all the possible lines of best fit i could have drwan but this value is the closest one to the actual value .. i thought i made a mess of my graph. Normally i'd get a value of about 6*10^-34 Js ( i got that value in one of the other past paers)
And btw i am pretty sure that we were not supposed to start the graph from the origin .. i started both scales from one and went all the way up to 2 ( up to 2.7 on the horizontal scale)
Please share your ideas with me .. i hope i am right
4. (Original post by justinawe)
Yeah, I got 4.00 x 10-34... I'm not too sure how some people on here got more than 5
i got 5.21*10^-34 Js
That is because starting from the origin is a bad idea since all your points will cluster at one end .. i have read many examiner reports and they do penalise you if you do that (Even if the line goes through the origin, and this one does)
I have even discussed it with my teacher
As for the units , yeah i have written the same thing (10^6 m^-1)
and i thought my answer was way off :P since it should be at least 6 (for me to feel comfortable :P)
5. (Original post by justinawe)
I'm definitely not promoting my answer as the correct one though. To be honest I'd be more confident in my answer if I'd got 5 like your friends, since it's closer to the real value. I may be good at maths, but my graph drawing is terrible, so your friends may very well have gotten a "better" answer than me.
Well, almost all my friends didn't draw from the origin, so they got a higher gradient by drawing a best fit line that crossed the x axis, but obviously that is wrong as the y intercept is 0. If graph was drawn in that way, they would have got a larger gradient which leads to a larger planck constant such as 5.

One more thing, if you break the scale, your graph should still cross the origin right?

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6. (Original post by Relaxedexams)
Well, almost all my friends didn't draw from the origin, so they got a higher gradient by drawing a best fit line that crossed the x axis, but obviously that is wrong as the y intercept is 0. If graph was drawn in that way, they would have got a larger gradient which leads to a larger planck constant such as 5.

One more thing, if you break the scale, your graph should still cross the origin right?

Posted from TSR Mobile
I don't think graph would go through origin. Was there a systematic error? In voltmeter.
7. Anyone knows whether the Planck constant we obtained from the gradient needed a unit?
8. I plotted Wavelenght against 1/wavelenght but in my axis i put Voltage(volts) and 1/wavelenght. How many points out of 5 would i gain?
would this affect me on the Next planck constant one where i needes to use the gradient?
9. (Original post by Relaxedexams)
My graph went through origin, cutting 3 points but I used a scale of 1 every 10 squares, so my gradient was 0.68

Got planks constant as 3.x * 10^28. Didn't multiply it by 10^6 either...

How much do you reckon I'll get for graph + plank constant out of 11?

Posted from TSR Mobile
Quite ironically i got the same gradient(it was 0.6something),same plank constant,same mistake-didn't multiply by 10^6 and ofc the graph didn't pass through the origin

my planck constant was 3.40 x 10^-28.

What reason did u give?
10. (Original post by TheKingOfTSR)
I don't think graph would go through origin. Was there a systematic error? In voltmeter.
Systematic error in voltmeter was not mentioned.

If y intercept is 0 graph has to go through origin. How can it not?

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11. (Original post by Relaxedexams)
Systematic error in voltmeter was not mentioned.

If y intercept is 0 graph has to go through origin. How can it not?

Posted from TSR Mobile
Well not necessarily.If you start from the origin but scale it then it wouldn't.For example see below;

12. (Original post by x0x)
Hey guys
I got a value of 5.2*10^-34 Js
i looked at all the possible lines of best fit i could have drwan but this value is the closest one to the actual value .. i thought i made a mess of my graph. Normally i'd get a value of about 6*10^-34 Js ( i got that value in one of the other past paers)
And btw i am pretty sure that we were not supposed to start the graph from the origin .. i started both scales from one and went all the way up to 2 ( up to 2.7 on the horizontal scale)
Please share your ideas with me .. i hope i am right
I totally agree with you my graph did start from 1 at both axes more or less and my line of best fit didnt touch x or y axis just a straight line through points and yea i got 5.2more or less.. what was your main uncertainty or error for h?
13. What where the adv and disadv for using micrometer or metre ruler?
14. (Original post by Relaxedexams)
Systematic error in voltmeter was not mentioned.

If y intercept is 0 graph has to go through origin. How can it not?

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Because of systematic error.
Same thing as: If equation shows a straight line why doesn't all the points lie on a straight line?
Because of systematic and random errors and wrong data provided.

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15. (Original post by StUdEnTIGCSE)
Because of systematic error.
Same thing as: If equation shows a straight line why doesn't all the points lie on a straight line?
Because of systematic and random errors and wrong data provided.

Posted from TSR Mobile
So even if you don't break the graph, it doesn't cut the origin? Because of errors? We had to assume all that and draw a graph? Damn I only thought no y intercept, so cuts through origin

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16. What were the possible answer for the very last question asking why the value obtained for Planks constant was lower than the actual value?
17. (Original post by StUdEnTIGCSE)
mega m^-1 should have been microm^-1,mustn't it?
Because to get 1/lambda they had first divided by 10^3 converting the nm to micrometer then inversed it.

A unit and its prefix go as one unit, doesn't it? So mega m-1 isnt mega^-1 m^-1.
In chemistry we have done IR spectroscopy. The wavelength of IR was in cm and when to convert to wave number (number of waves per cm) which was also 1/lambda the units were cm^-1.

So in that question 1/lambda meant number of waves in a micrometer length.

The meter rule method had GREATER uncertainty and you should prove why it was so? ?

Posted from TSR Mobile
I'm not sure about whether what you're saying is right or not about the prefix, but it doesn't matter, we'll see what they'll accept and what not.

What did you write for it? And could you please tell me how many marks you think I'll lose for that silly gradient mistake? Thanks.
18. What were the grade boundaries for A in May 2012 and jan 2013?

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19. (Original post by l-g)
What were the possible answer for the very last question asking why the value obtained for Planks constant was lower than the actual value?
I wrote systematic errors in the voltmeter like zero errors and parallax while reading it.
20. (Original post by Relaxedexams)
What were the grade boundaries for A in May 2012 and jan 2013?

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May 12 was 29, Jan 13 was 32.

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