5.7- THE DIFFRACTION GRATING Flashcards

1
Q

What does a diffraction grating consist of?

A

plate with many closely spaced parallel slits ruled on it

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2
Q

What happens when a parallel beam of monochromatic light is directed normally at a diffraction grating?

A

light transmitted by grating in certain directions only

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3
Q

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)

A

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

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4
Q

What is the central beam referred to as? (diffraction grating)

A

zero order beam

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5
Q

What is the zero order beam in the same direction as?

A

incident beam

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6
Q

What are the other transmitted beam numbered outwards from? (diffraction grating)

A

from zero order beam

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7
Q

What does the angle of diffraction between each transmitted beam + central beam be increased by? (2)

A

light of longer wavelength used (e.g. replacing blue filter with red filter)

grating with closer slits used

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8
Q

What does each slit do as light passes through it? (diffraction grating)

A

each slit diffracts light waves passing through it

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9
Q

What happens as each diffracted wavefront emerges from the slit? (diffraction grating)

A

it reinforces a wavefront from a slit adjacent to it

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10
Q

Diffracting grating equation for angle of diffraction of nth order beam

A

dsinθ = nλ

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11
Q

Equation for the number of slits per metre on the grating?

A

N = 1 / d

d= grating spacing

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12
Q

For a given order and wavelength, what happens the greater the value of d?
d= grating spacing

A

greater the angle of diffraction

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13
Q

What happens the larger the number of slits per metre?

A

bigger the angle of diffraction

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14
Q

What is the maximum number of orders given by?

A

value of d/λ rounded down to nearest whole number

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15
Q

What is the spectrum of the spectrum of light from a filament lamp?

A

continuous spectrum of colour from deep violet at about 350nm to deep red at about 650nm

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16
Q

What is the most intense part of the continuous spectrum dependent on?

A

temperature of light source

17
Q

What happens the hotter the light source? (continuous spectrum)

A

shorter the wavelength of brightest part of spectrum

18
Q

What can be measured by measuring the wavelength of the brightest part of the continuous spectrum?

A

can measure temperature of light source

19
Q

Example of light sources that emit light at specific wavelengths?

A

glowing has in vapour lamp or discharge tube

20
Q

What does the spectrum of glowing gas in a vapour lamp or discharge tube consist of as it emits light at specific wavelengths?

A

consists of narrow vertical lines of different colours

21
Q

What are the wavelengths of the lines on a line emission spectra the characteristics of?

A

characteristic of chemical element that produced the light

22
Q

If a glowing gas contains more than one element, how can the elements be identified?

A

elements in gas can be identified by observing its line spectrum

23
Q

What is a line absorption spectra?

A

continuous spectrum with narrow dark lines at certain wavelengths

24
Q

What is observed after spectrum of light from a filament lamp passed through glowing gas?

A

think dark vertical lines superimposed on continuous spectrum

25
Q

What is the pattern of dark lines observed after spectrum of light from filament lamp passed through glowing gas due to?

A

due to elements in glowing gas

26
Q

What do the elements in the glowing gas do? (line absorption spectra)

A

absorb light of same wavelengths they can emit so transmitted light is missing these wavelengths

27
Q

What do the atoms of the glowing gas that absorb light then do? (line absorption spectra)

A

emit light subsequently but not necessarily in same direction as transmitted light