5.7- THE DIFFRACTION GRATING Flashcards
What does a diffraction grating consist of?
plate with many closely spaced parallel slits ruled on it
What happens when a parallel beam of monochromatic light is directed normally at a diffraction grating?
light transmitted by grating in certain directions only
Why is it that when a parallel beam of monochromatic light is directed normally at diffraction grating, light transmitted by grating in certain directions only? (2)
light passing through each slit diffracted
diffracted light waves from adjacent slits reinforce each other in certain directions only, including incident light direction + cancel out in all other directions
What is the central beam referred to as? (diffraction grating)
zero order beam
What is the zero order beam in the same direction as?
incident beam
What are the other transmitted beam numbered outwards from? (diffraction grating)
from zero order beam
What does the angle of diffraction between each transmitted beam + central beam be increased by? (2)
light of longer wavelength used (e.g. replacing blue filter with red filter)
grating with closer slits used
What does each slit do as light passes through it? (diffraction grating)
each slit diffracts light waves passing through it
What happens as each diffracted wavefront emerges from the slit? (diffraction grating)
it reinforces a wavefront from a slit adjacent to it
Diffracting grating equation for angle of diffraction of nth order beam
dsinθ = nλ
Equation for the number of slits per metre on the grating?
N = 1 / d
d= grating spacing
For a given order and wavelength, what happens the greater the value of d?
d= grating spacing
greater the angle of diffraction
What happens the larger the number of slits per metre?
bigger the angle of diffraction
What is the maximum number of orders given by?
value of d/λ rounded down to nearest whole number
What is the spectrum of the spectrum of light from a filament lamp?
continuous spectrum of colour from deep violet at about 350nm to deep red at about 650nm
What is the most intense part of the continuous spectrum dependent on?
temperature of light source
What happens the hotter the light source? (continuous spectrum)
shorter the wavelength of brightest part of spectrum
What can be measured by measuring the wavelength of the brightest part of the continuous spectrum?
can measure temperature of light source
Example of light sources that emit light at specific wavelengths?
glowing has in vapour lamp or discharge tube
What does the spectrum of glowing gas in a vapour lamp or discharge tube consist of as it emits light at specific wavelengths?
consists of narrow vertical lines of different colours
What are the wavelengths of the lines on a line emission spectra the characteristics of?
characteristic of chemical element that produced the light
If a glowing gas contains more than one element, how can the elements be identified?
elements in gas can be identified by observing its line spectrum
What is a line absorption spectra?
continuous spectrum with narrow dark lines at certain wavelengths
What is observed after spectrum of light from a filament lamp passed through glowing gas?
think dark vertical lines superimposed on continuous spectrum
What is the pattern of dark lines observed after spectrum of light from filament lamp passed through glowing gas due to?
due to elements in glowing gas
What do the elements in the glowing gas do? (line absorption spectra)
absorb light of same wavelengths they can emit so transmitted light is missing these wavelengths
What do the atoms of the glowing gas that absorb light then do? (line absorption spectra)
emit light subsequently but not necessarily in same direction as transmitted light
