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# Edexcel IAL Physics Unit 3 WPH03 May June 2016 Discussion

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1. (Original post by Blazyy)
I put in parallax error when placing the pins, is that also correct?
ummmmm, what do you mean by pins?
My gradient was 5, my resistivity was 1.23*10^-6
Exact same

What did you write for the "comment on safety" for the refractive index experiment?

Also for the how to find refractive index question i wrote
Refractive index = Sin I / Sin r
Take a reading of angle of incidence and refraction from the graph
Multiply them by sin and divide to find refractive index

Is that correct?
3. (Original post by Blazyy)
I put in parallax error when placing the pins, is that also correct?
Nevermind, ignore my question
4. (Original post by Ali Bizri)
Exact same

What did you write for the "comment on safety" for the refractive index experiment?

Also for the how to find refractive index question i wrote
Refractive index = Sin I / Sin r
Take a reading of angle of incidence and refraction from the graph
Multiply them by sin and divide to find refractive index

Is that correct?
I put: draw a graph of sin 1 against sin r and calculate the gradient which will give you the refractive index. For safety, I said don't point the ray box towards yours and others' eyes as the laser can damage your eyes,
5. (Original post by Blazyy)
Nevermind, ignore my question
If you mean put the pins along the refracted ray, then yeah it makes sense that there would be a parallex error there.
6. (Original post by Ali Bizri)
Exact same

What did you write for the "comment on safety" for the refractive index experiment?

Also for the how to find refractive index question i wrote
Refractive index = Sin I / Sin r
Take a reading of angle of incidence and refraction from the graph
Multiply them by sin and divide to find refractive index

Is that correct?
For safety I wrote low voltage

but for refractive index calculation they asked for graphical calculation, so you had to say draw a graph of sin i on sin r and find gradient
Yeah, But the second and third point was out of the best fit line
I got a value of 4.91 fr gradient! :/
8. (Original post by don't cry-craft)
I put: draw a graph of sin 1 against sin r and calculate the gradient which will give you the refractive index. For safety, I said don't point the ray box towards yours and others' eyes as the laser can damage your eyes,
That makes sense, the answers should be identical for both methods so I don't think it'll be a big deal, for safety i said that this is a low risk experiment and i added one more point which was the risk of falling block so wear foot protection.
Parallax error for protractor lol
how can there be a parallax error since the protractor would be flat against the paper to measure the angle?
For safety I wrote low voltage

but for refractive index calculation they asked for graphical calculation, so you had to say draw a graph of sin i on sin r and find gradient
What did you write to "comment on her plan" when she measured the time as 3s for a trolley to go down a slope?
11. It should be on your eye level horizontally , like you need to make your eyes directly parallel to the measurement, some people can stand away from the protractor and count.
12. (Original post by Sunethra)
What did you write to "comment on her plan" when she measured the time as 3s for a trolley to go down a slope?
I wrote there would be human reaction time error, so an electronic timer would be better for accurate results.
It should be on your eye level horizontally , like you need to make your eyes directly parallel to the measurement, some people can stand away from the protractor and count.
I said parralex errors when using protractor and I said other rays might be incident on the glass block so in brackets I said do the experiment in a dark room
I wrote there would be human reaction time error, so an electronic timer would be better for accurate results.
yeah same, especially since 3s is a very short amount of time.
15. (Original post by Sunethra)
What did you write to "comment on her plan" when she measured the time as 3s for a trolley to go down a slope?
I measured the persentage uncertainty by doing 0.38/3 *100 and found about 12.5% and commented that it is too high
16. (Original post by Sunethra)
I said parralex errors when using protractor and I said other rays might be incident on the glass block so in brackets I said do the experiment in a dark room
Oh okay, I said that there's an uncertainty of 0.5 degrees when taking the readings, especially since the angles can be quite small. Would this be okay?
17. Guys my value for resistivity was 4.6x10^-6? i think i did something wrong when finding the area of the wire but my gradient was 4.5? i thing im out of the range of what they would expect
18. hey my exam was good. is the graph supposed to be a straight line or a curvy type of thing.
if i used the right method to find gradient and the value of resistivity but got the wrong answer will i get any marks.
ummmmm, what do you mean by pins?
Sometimes when you don't have a ray box in hand, you use pins to mark the incident and refracted ray.
20. (Original post by Suhaib.134)
Guys my value for resistivity was 4.6x10^-6? i think i did something wrong when finding the area of the wire but my gradient was 4.5? i thing im out of the range of what they would expect
did u convert the diameter to radius? Gradient was 4.96 i think so when u round it would be 5 not sure if urs was right.

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