# P3 GCSE Edexcel Physics Extension Unit

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#1
'sini / sinr = constant' what does this mean? (page 191 in the green text book)
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5 years ago
#2
Im not sure but sin i is the angle of incidence and sin r is the angle of reflection 0
5 years ago
#3
It gives you the value of the refractive index

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#4
(Original post by kingaaran)
It gives you the value of the refractive index

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refractive index of what? the material the ray is going into or from?
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#5
e is the charge on an electron in the equation:
KE=eV
e = 1.6x10-19C
will this number be given to us in the question? (its not in the formula page with the equation.
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5 years ago
#6
(Original post by jillifish)
refractive index of what? the material the ray is going into or from?
The formula comes from Snell's Law: Nr = this is the refractive index of the substance that light is going into.
Ni = this is the refractive index of the substance that light is coming out of, before it enters the refractive medium.
I = incident Ray angle
R = refractive Ray angle.

The equation in your book omits the denominator on the left hand side of the equation, because you'll get examples of going from air into something. Since the refractive index of air is 1, you're simply left with Hence, the formula will give you the refractive index of the medium that the light is entering.

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5 years ago
#7
(Original post by jillifish)
e is the charge on an electron in the equation:
KE=eV
e = 1.6x10-19C
will this number be given to us in the question? (its not in the formula page with the equation.
I have seen that number on A Level Physics Formula sheets, so I'm sure they wouldn't be expecting you to remember that. Youshould be getting that in the question.

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#8
(Original post by kingaaran)
The formula comes from Snell's Law: Nr = this is the refractive index of the substance that light is going into.
Ni = this is the refractive index of the substance that light is coming out of, before it enters the refractive medium.
I = incident Ray angle
R = refractive Ray angle.

The equation in your book omits the denominator on the left hand side of the equation, because you'll get examples of going from air into something. Since the refractive index of air is 1, you're simply left with Hence, the formula will give you the refractive index of the medium that the light is entering.

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thankyou!
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5 years ago
#9
Can someone explain the critical angle and total internal reflection? 0
5 years ago
#10
(Original post by jillifish)
e is the charge on an electron in the equation:
KE=eV
e = 1.6x10-19C
will this number be given to us in the question? (its not in the formula page with the equation.
My teacher said it is very probable that it won't as the examiners have said that they will not include things that "the students should know given they are working at a further additional level" so learn it to be safe
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5 years ago
#11
(Original post by TJHughes)
My teacher said it is very probable that it won't as the examiners have said that they will not include things that "the students should know given they are working at a further additional level" so learn it to be safe
(Original post by jillifish)
e is the charge on an electron in the equation:
KE=eV
e = 1.6x10-19C
will this number be given to us in the question? (its not in the formula page with the equation.
I think your teacher is just trying to scare you, because if the number is given at A Level then I'd expect it to be given at GCSE.

Oh, and the number has a negative in front of it btw

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5 years ago
#12
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5 years ago
#13
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#14
i can only find two past papers for this exam: the SAM and June 2013. 0
5 years ago
#15
How's everyone feeling about this exam ? I think it's defo the hardest. 0
5 years ago
#16
(Original post by Marcusroye98)
Can someone explain the critical angle and total internal reflection? The critical angle is the angle that the angle of incidence (the ray of light entering the prism/medium) needs to be so any rays of light that exit the medium do so at the boundary (90 degrees) to the medium.

Total internal reflection occurs when the angle of incidence is GREATER than the critical angle, and it is when the ray of light hits the boundary and all of it is reflected back (none of it exits the boundary) resulting in all the light to be internally reflected (used for optical fibres which are used in endoscopes and some communications technology)
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5 years ago
#17
THANK-YOU I am really confused, do you know the calculation to work out the focal length ( 1/f = 1/u +1v) does it have to be in cm or m?
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5 years ago
#18
(Original post by jillifish)
i can only find two past papers for this exam: the SAM and June 2013. There's June 2013, Sample Assessment Material and Additional Sample Assessment Material, this should be on Edexcel's website? My teacher just printed them all out for me, with the SAMs the mark schemes are at the back. Good luck **Edit**
I found just found the link for it online, couldn't find it on Edexcel's website.
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5 years ago
#19
(Original post by Marcusroye98)
THANK-YOU I am really confused, do you know the calculation to work out the focal length ( 1/f = 1/u +1v) does it have to be in cm or m?
that depends if the answer units are CM or M... If the question is in M but the answer space has CM then you convert. If the question has M and the answer space has M then you just work it out... no conversion
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5 years ago
#20
(Original post by Marcusroye98)
THANK-YOU I am really confused, do you know the calculation to work out the focal length ( 1/f = 1/u +1v) does it have to be in cm or m?
Basically what angelo said, i don't believe it matters so long as you use the same unit throughout the equation. i usually convert to meters though but that is just my personal preference.
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