diffraction grating Flashcards
Describe the fringe pattern from a diffraction grating compared to that of a double slit.
- thinner distinct
- more fringes
- equally spaced
How are fringes ordered in diffraction grating?
- central fringe = 0 order
- adjacent fringes increases from 1
What must the path difference be for constructive interference to occur?
a whole number of wavelengths i.e even number of half wavelengths
How are paths from a diffraction grating to the screen modelled as and why?
modelled as parallel bc the distance from grating to screen is significantly larger than the grating spacing
State the equation for path difference.
nλ = d sin(θ)
State what happens to fringe spacing when the distance to the screen increases.
increases
State what happens to fringe spacing when the wavelength increases and why.
- increases
- as path difference increases (nλ)
- so angle of diffraction increases
State what happens to fringe spacing when the grating spacing increases and why.
- decreases
- as angle of diffraction decreases
- (to keep path difference constant)
State how to find the grating spacing.
d = 1/N
where N is no. of lines per metre
State what happens to fringe spacing when number of lines on the diffraction grating increases.
- d decreases (1/N)
- sin(θ) increases
- w increases
Explain how to find the maximum order number.
n = d sin(90)/λ
round down to nearest whole no.
State two applications of diffraction grating.
→ used in spectrometers to:
- analyse light from stars
- chemical analysis
- measure red shift
→ x-ray crystallography
Briefly explain how x-ray crystallography uses diffraction grating.
→ x-rays directed at thin crystal sheet
→ gaps between atoms in a crystal are similar in size to wavelength of x-rays
→ therefore crystal acts as diffraction grating, forming a diffraction pattern which is used to find atomic spacing
