Jennifer50
Badges: 4
Rep:
?
#1
Report Thread starter 4 years ago
#1
What is path difference?
0
reply
Kozmo
Badges: 10
Rep:
?
#2
Report 4 years ago
#2
A diffraction grating is simply a plate with many, incredibly small and very closely spaced parallel slits ruled into it.
Based upon the close proximity of said slits a very sharp interference pattern is produced (much better and clearer than with Young's Double slits) when a source of monochromatic and coherent light is passed through it.
This is due to the fact that there's such a large proportion of diffraction gratings interfering (experiencing superposition).
Waves that meet 180 degrees out of phase experience destructive interference and so produce a sharp minimum (dark point), and light rays that meet in phase (or 360 degrees out of phase) experience constructive interference and so produce a sharp maxima (bright point).

The diffraction grating equation is (for my spec - AQA):

n Image = d sin( Image )

where:

n = the order of the beam produced
d = distance between two slits in the diffraction grating (often extremely small)
Image = the wavelength of the incident light being diffracted by the grating.
Image= the angle between the order beam in question (a maxima) and the zero order (normal).
2
reply
Jennifer50
Badges: 4
Rep:
?
#3
Report Thread starter 4 years ago
#3
What do you mean by the order bit for the angle?
0
reply
Kozmo
Badges: 10
Rep:
?
#4
Report 4 years ago
#4
(Original post by Jennifer50)
What do you mean by the order bit for the angle?
When we put monochromatic and coherent light through a diffraction grating we'll have a number of maximum points produced. These, we refer to as maximum orders (you get a first order maximum produced on either side of the zero order) - the angle between an order beam and the zero order (the normal line - the most intense maxima) is dependent on the wavelength of light, the distance from the screen to the grating and the slit separation within the grating, s.

n Image / d = sin( Image )

We can see this when we rearrange the diffraction grating equation.
We can therefore say as we increase Image diffraction increases (the waves spread out more) and so Image is greater - all just from looking at the grating equation
0
reply
Jennifer50
Badges: 4
Rep:
?
#5
Report Thread starter 4 years ago
#5
What does coherent light mean?
0
reply
M0nkey Thunder
Badges: 13
Rep:
?
#6
Report 4 years ago
#6
(Original post by Jennifer50)
What does coherent light mean?
It means that the 2 waves produced have: a fixed phase difference, same frequency and same wavelength. Having coherent waves makes the interference pattern a lot clearer.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (627)
33.66%
Yes, I like the idea of applying to uni after I received my grades (PQA) (784)
42.08%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (368)
19.75%
I think there is a better option than the ones suggested (let us know in the thread!) (84)
4.51%

Watched Threads

View All