# June 2011- OCR Physics G482

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Thread starter 5 years ago
#1
For 6ai,why is a single slit needed to make the light coherent at the double slits? won't they still be coherent without the single slit as they from one source and when they are diffracted by the double slits they are in phase
For question 7a,
the mark scheme says:
reference to a transverse wave or to vibrations in plane normal to the direction of (energy) propagation. oscillations/vibrations in one direction only/confined to single plane (containing the direction of propagation)

but i think where they said
vibrations in plane normal to the direction of (energy) propagation
it is contradicted by
oscillations/vibrations in one direction only (containing the direction of propagation)
also for 7b, the examiner's report says the reflecting surface acts as a polariser but it isn't is, it it just plane polarises the waves and you don't even need to rotate the second polariser because either the vertical is completely blocked or horizontal is completely blocked
and for 7c the mark scheme says when θ is 90o minimum/zero intensity transmitted/image dim/vanished. well we proved in the previous part it cant be zero
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Thread starter 5 years ago
#2
(Original post by runny4)
For 6ai,why is a single slit needed to make the light coherent at the double slits? won't they still be coherent without the single slit as they from one source and when they are diffracted by the double slits they are in phase
For question 7a,
the mark scheme says:
reference to a transverse wave or to vibrations in plane normal to the direction of (energy) propagation. oscillations/vibrations in one direction only/confined to single plane (containing the direction of propagation)

but i think where they said
vibrations in plane normal to the direction of (energy) propagation
it is contradicted by
oscillations/vibrations in one direction only (containing the direction of propagation)
also for 7b, the examiner's report says the reflecting surface acts as a polariser but it isn't is, it it just plane polarises the waves and you don't even need to rotate the second polariser because either the vertical is completely blocked or horizontal is completely blocked
and for 7c the mark scheme says when θ is 90o minimum/zero intensity transmitted/image dim/vanished. well we proved in the previous part it cant be zero
heres the paper
0
5 years ago
#3
(Original post by runny4)
For 6ai,why is a single slit needed to make the light coherent at the double slits? won't they still be coherent without the single slit as they from one source and when they are diffracted by the double slits they are in phase
For question 7a,
the mark scheme says:
reference to a transverse wave or to vibrations in plane normal to the direction of (energy) propagation. oscillations/vibrations in one direction only/confined to single plane (containing the direction of propagation)

but i think where they said
vibrations in plane normal to the direction of (energy) propagation
it is contradicted by
oscillations/vibrations in one direction only (containing the direction of propagation)
also for 7b, the examiner's report says the reflecting surface acts as a polariser but it isn't is, it it just plane polarises the waves and you don't even need to rotate the second polariser because either the vertical is completely blocked or horizontal is completely blocked
and for 7c the mark scheme says when θ is 90o minimum/zero intensity transmitted/image dim/vanished. well we proved in the previous part it cant be zero
For double slit diffraction, the two light sources must be coherent. If you have a sodium lamp at a distance from two slits, there will be some path difference. and so it will end up incoherent (?). Having a single slit fixes that. To behonest, they only wanted any method of producing coherent light, so saying "use a laser" might be worth the mark. I'm not used to OCR mark schemes.

For 7, the point is that the reflected light is polarised (at 53o), but you can only tell that by taking a polarising filter and rotating it to see if the light gets through. If it is only partially polarised, then no angle will completely block the light, whereas for fully polarised light the filter will block it all at one specific angle.

For 7(c), Malus' law only applies to fully polarised light, and yes, the transmittance of that can be 0 through a polariing filter if they are at 90o to each other.
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