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# The Physics PHYA2 thread! 5th June 2013 Watch

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1. (Original post by tom160)
Explanation for Jan 2013 q7 b(ii) please?
Just count the total amount of waves
2. What are the 3 graphs of intensity for single slit , double slit and grating suppose to look like ?

thanks

3. (Original post by Claree)
Speed of microwaves is the speed of light. Microwaves are electromagnetic waves, just like visible light. All EM waves have the same speed.
Thank you!!
4. (Original post by Jack93o)
okay, you're told that both those waves are moving towards the left

P would move up, because left of P is a peak. As whole wave moves to the right, the peak will go through point P, forcing it upwards

wave B is a longitudinal wave, instead of moving up and down (like in wave A), the particles will move left and right along the same line as where the wave is moving. Q will shift to the left, because an area of compression is left of Q. So as the wave continues moving along to the right, that area of compression will pass through point Q, pulling it leftwards
you absolute beast
5. (Original post by Greasy Gorilla)
What is the difference between a fringe and a Maxima in single slit diffraction?
They are the same thing, the light fringes are the maxima where the waves meet in phase, whilst the dark fringes are the minima where the waves meet out of phase.
6. (Original post by Nav_Mallhi)
Refraction is basically the bending of light.
If the ray goes from a material of a lower refractive index to a higher refractive index, it will bend TOWARDS the normal and vica versa.

(Original post by Raimonduo)
A higher refractive index. When a light ray enters a substance which has a higher refractive index, than the incidence substance, it will refract TOWARDS THE NORMAL. Thus, the higher the refractive index of the substance, the more it refracts towards the normal.
Thanks
7. (Original post by BayHarborButcher)
But I dont understand, doesn't that mean it always happens as long as a ray is refracted? But this was the only question I've seen that asked you to show it.
Yes! A refracted ray has an angle less than or equal to the critical angle. When the incident angle is = to the critical angle, you will have an emergent ray parallel to the substance. But, increasing the incident angle bigger than to the critical angle(incident angle exceed the critical angle), total internal reflection occurs. Is that clear now m8?
8. (Original post by StalkeR47)
Just learned something in the first 55 seconds haha

BTW are we allowed to draw in pencil if they ask us to do graph?
9. Does anyone know how to explain how to derive the d sin theta = n lambda question?
10. (Original post by v.007)
What are the 3 graphs of intensity for single slit , double slit and grating suppose to look like ?

thanks

I'm wondering this too!! Someone help please!
11. (Original post by Anonymous1717)
Does anyone know how to explain how to derive the d sin theta = n lambda question?
http://www.thestudentroom.co.uk/show...age=54&page=54
12. (Original post by Dingo749)
Currently sat wishing I had the motivation to revise for this :')Posted from TSR Mobile
Thank god I'm not the only one
13. (Original post by Qari)
Just learned something in the first 55 seconds haha

BTW are we allowed to draw in pencil if they ask us to do graph?
Yes you can! It even says on the first page of the paper. "USE PENCIL ONLY FOR DRAWINGS".
14. (Original post by Claree)
How does a node form? (with regards to phase/phase difference and cancellation)
As the waves move through each other this is the point where the 2 waves cancel each other out however are still in phase.
15. I seriously just can't come to terms with this diffraction business with how the equations are derived. Where they talk about there being similar triangles and first order and second order and wavelength differencesCould anyone explain it simply for me pleaseeeMy text book makes no sense
16. (Original post by masryboy94)
lets say the distance between the centre of 2 adjacent slits is 'd' which can be worked out by doing . so as the wavefront of the source comes in, it diffracts at an angle towards the screen, this can be calculated by using a protractor or a spectrometer. if you get constructive interference you know that the path difference for say the first order is . now using some trig, we know that . sub in and 'd' to give . which gives . now for every maxima or order on the screen, that means you are getting constructive interfence, therefore the path difference with always have to be a whole number (integer) multiple of , so lets call that . therefore you get

on diagram A to C is
Can you derive fringe spacing for us?
17. (Original post by Greasy Gorilla)
What is the difference between a fringe and a Maxima in single slit diffraction?
You can refer to fringes as being dark (where the waves interfere destructively) or light (the opposite), maxima refers to just light fringes e.g. central maxima, first order maxima, etc

(Original post by Claree)
How does a node form? (with regards to phase/phase difference and cancellation)
This is what you need to say:
When 2 similar waves travelling in opposite directions, they superpose to form a stationery wave. Nodes are formed when the 2 similar waves interfere destructively
18. anyone have or know where i can find the January 2013 paper for physics. Really need it cause i missed my mock and thats the only paper i havent got at the moment!
Ill realllllyyyyy appreciate it
19. (Original post by tom160)
Explanation for Jan 2013 q7 b(ii) please?
This one is a bit cheeky to be honest.

Firstly, you'll need the wavelength from part q7 b(i), in order to work this question out.
Then, count the amount of peaks and troughs of each wave. Keep in mind, 1 peak + 1 trough = 1 wavelength. Thus, when you've found the the amount of peaks and troughs in each wave, they should have a difference of 1 peak and 1 trough. Which makes the path difference
20. (Original post by StalkeR47)
For that question, could you possibly correct me if I'm wrong?

The ray hits the glass-air boundary at an angle of incidence of 50 degrees.

The ray is then totally internally reflected away from the normal and at the glass-water boundary, it again refracts away from the normal. TIR is 90 degrees right? So the angle of reflection would be 90-50=40 degrees?

At the water oil boundary, the ray refracts away from the normal through the glass container.

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