Diffraction grating Flashcards
what is a diffraction grating?
a plate with many closely spaced parallel slits
Why is the monochromatic light only directed in certain directions?
the ligh passing through each slit is diffracted
the diffracted light waves from adjacent slits reinforce each other in certain directions only, including the incident light direction and cancel out all other directions
What is the central beam referred to as?
the zero order beam is in the same direction as the incident beam
the other transmitted beams are numbered outwards from the zero order beam
How does the angle of diffraction between each transmitted beam and the central beam increase?
light of longer λ
a grating with closer slits is used
What is the diffraction grating equation?
d sin θ = n λ
n = order d = diffraction grating gap
what is the equation for the number of slits per metre?
1 / d
What effect does the number of slits have on the angle of diffraction?
increases it
What is the equation to find the number of orders produceD?
n = d / wavelength
rounded down to the nearest whole number
What is continuous spectra
continuous spectrum of colour from deep violet (350nm) to deep red (650 nm)
most intense part depends on the temperature of the light source
hotter the source the shorter the wavelength on the brightest part of the spectrum
what is line emission spectra?
a glowing gas in a vapour or a discharge tube emit light at specific wavelengths, so its spectrum consists of narrow vertical lines of different colours
characteristic of the chemical element that produced it
What is line absorbtion spectra?
continuous spectrum with narrow dark lines at certain wavelengths
e.g. if the spectrum of light from a filament is observed after passing it through a glowing gas, thin dark vertical lines are obvserved superimposed on the continuous spectrum
due to the elements in the glowing gas that absorb light of the same wavelengths, they can emit at so the transmitted light is missing
