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# Edexcel Physics Unit 3 9th May Watch

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1. (Original post by StUdEnTIGCSE)
Prefix are considered part of a unit so microm^-1 is 1/microm, which makes sense.

Its a wave number, we studied this in Chem. I might have got confused

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1/micro is mega.

I didn't study it anywhere, but it makes mathematical sense really

I'll demonstrate this with an example.

The first wavelength was 630 nanometres I believe, and the inverse given was 1.59.

Let's make this simple and convert it all to SI units first.

630 nanometres is .

Inverse this, and we get 1590000 m-1 to 3 s.f.

Which is 1.59 Mega m-1!
2. (Original post by justinawe)
1/micro is mega.

I didn't study it anywhere, but it makes mathematical sense really

I'll demonstrate this with an example.

The first wavelength was 630 nanometres I believe, and the inverse given was 1.59.

Let's make this simple and convert it all to SI units first.

630 nanometres is .

Inverse this, and we get 1590000 m-1 to 3 s.f.

Which is 1.59 Mega m-1!
Wrong!
How did you state it in the answer?
Mm^-1?
That's wrong ( but they might accept!)
Real way is to put as micro+meter+^-1 (no spaces in between)
Don't get me wrong!
I know that the correct answer is 10^6 * m^-1 but you can't simply replace 10^6 with M.
What you can do is replace it with (micro symbol) .it will be treated as a part of the unit.
HERE IS SOME PROOF:
6.2.3 Inseparability of prefix and unit The grouping formed by a prefix symbol attached to a unit symbol constitutes a new inseparable symbol (forming a multiple or submultiple of the unit concerned) which can be raised to a positive or negative power and which can be combined with other unit symbols to form compound unit symbols. Examples: 2.3 cm3 = 2.3 (cm)3 = 2.3 (10−2 m)3 = 2.3 × 10−6 m3 1 cm−1 = 1 (cm)−1 = 1 (10−2 m)−1 = 102 m−1 5000 µs−1 = 5000 (µs)−1 = 5000 (10−6 s)−1 = 5000 × 106 s−1 = 5 × 109 s−1 1 V/cm = (1 V)/(10−2 m) = 102 V/m Prefix names are also inseparable from the unit names to which they are attached. Thus, for example, millimeter, micropascal, and meganewton are single words
3. (Original post by TheKingOfTSR)
Wrong!
How did you state it in the answer?
Mm^-1?
That's wrong ( but they might accept!)
Real way is to put as micro+meter+^-1 (no spaces in between)
Don't get me wrong!
I know that the correct answer is 10^6 * m^-1 but you can't simply replace 10^6 with M.
What you can do is replace it with (micro symbol) .it will be treated as a part of the unit.
HERE IS SOME PROOF:
6.2.3 Inseparability of prefix and unit The grouping formed by a prefix symbol attached to a unit symbol constitutes a new inseparable symbol (forming a multiple or submultiple of the unit concerned) which can be raised to a positive or negative power and which can be combined with other unit symbols to form compound unit symbols. Examples: 2.3 cm3 = 2.3 (cm)3 = 2.3 (10−2 m)3 = 2.3 × 10−6 m3 1 cm−1 = 1 (cm)−1 = 1 (10−2 m)−1 = 102 m−1 5000 µs−1 = 5000 (µs)−1 = 5000 (10−6 s)−1 = 5000 × 106 s−1 = 5 × 109 s−1 1 V/cm = (1 V)/(10−2 m) = 102 V/m Prefix names are also inseparable from the unit names to which they are attached. Thus, for example, millimeter, micropascal, and meganewton are single words
I wrote
4. (Original post by StUdEnTIGCSE)
Prefix are considered part of a unit so microm^-1 is 1/microm, which makes sense.

Its a wave number, we studied this in Chem. I might have got confused

Posted from TSR Mobile
I think your correct!
5. (Original post by StUdEnTIGCSE)
Prefix are considered part of a unit so microm^-1 is 1/microm, which makes sense.

Its a wave number, we studied this in Chem. I might have got confused

Posted from TSR Mobile
Actually, after thinking about it, I believe you are right. My friends who wrote Mega m-1 managed to convince me they were right, but now I'm pretty sure they were wrong
6. (Original post by Aerosports)
Unofficial mark scheme:
1)B 2) D 3)C 4)B 5) C

7)Experiment for Spring constant

8) m = hc/e c = speed of light, e = electron charge

8 part c) Graph ,part d) find plancks constant ,part e)Suggest difference between real constant and your given constant i calculated 5.54x10 -34

btw the way i finished 20mins early
How did you get 5.54x10^-34?
What did you get for gradient. I got one hence I got h to be 5.3x10^-28
7. (Original post by thextractor007)
How did you get 5.54x10^-34?
What did you get for gradient. I got one hence I got h to be 5.3x10^-28
You forgot to consider the fact that the inverse wavelength wasn't in SI unit.
8. 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
9. i got h = 4.1x10^-34
almost everyone in class got that as well...
10. (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
1028 or 10-28? If it's the former, then that's way off.

Hmm, why would the scale change your gradient? It shouldn't make a difference what scale you'd use.

If you plotted the points correctly and did everything else right, it's probably an issue with your best fit line. I'd say 8 or 9 out of 11, if you did everything else right.
11. (Original post by Meera.S.)
i got h = 4.1x10^-34
almost everyone in class got that as well...
Yeah, I got 4.00 x 10-34... I'm not too sure how some people on here got more than 5
12. (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
Maybe 9?
- goes through origin(1)
- the axis (1)
-the triangle for the gradient(1)
- you did the y=mx+c (3)
- you found the inverse of the wavelengths (3)
13. (Original post by justinawe)
1028 or 10-28? If it's the former, then that's way off.

Hmm, why would the scale change your gradient? It shouldn't make a difference what scale you'd use.

If you plotted the points correctly and did everything else right, it's probably an issue with your best fit line. I'd say 8 or 9 out of 11, if you did everything else right.
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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14. i got 100 Hz for the mcq
how is the answer 250 Hz? ;/
15. (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 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.

Posted from TSR Mobile
16. (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.

Posted from TSR Mobile

if i were you, i would have rounded and gotten 4
17. i got some what 5.4*10^-34 it should be correct ans because it close to the original value also i tripled checked cause i finished the exam 15 earlier.
18. (Original post by justinawe)

Hmm, why would the scale change your gradient? It shouldn't make a difference what scale you'd use.
Well for those 1.4, 6.3 values, I rounded off and plotted points due to my scale which was congested, so gradient w ould have changed right?

Posted from TSR Mobile
19. (Original post by Meera.S.)
i got 100 Hz for the mcq
how is the answer 250 Hz? ;/
well each sqaure was 1ms, and a complete wave lenght was for 4ms that's the period for one wave lenght is 4*10-3 sec so to get frequency just inverse it
20. (Original post by ramanan)
i got some what 5.4*10^-34 it should be correct ans because it close to the original value also i tripled checked cause i finished the exam 15 earlier.
There will be a range of acceptable answers. Your value depends on how you drew your line of best fit, so naturally not everyone would arrive at the same answer.

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