5.7- THE DIFFRACTION GRATING

Question 1

What does a diffraction grating consist of?

Answer 1

plate with many closely spaced parallel slits ruled on it

Question 2

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

Answer 2

light transmitted by grating in certain directions only

Question 3

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)

Answer 3

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

Question 4

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

Answer 4

zero order beam

Question 5

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

Answer 5

incident beam

Question 6

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

Answer 6

from zero order beam

Question 7

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

Answer 7

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

grating with closer slits used

Question 8

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

Answer 8

each slit diffracts light waves passing through it

Question 9

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

Answer 9

it reinforces a wavefront from a slit adjacent to it

Question 10

Diffracting grating equation for angle of diffraction of nth order beam

Answer 10

dsinθ = nλ

Question 11

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

Answer 11

N = 1 / d

d= grating spacing

Question 12

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

Answer 12

greater the angle of diffraction

Question 13

What happens the larger the number of slits per metre?

Answer 13

bigger the angle of diffraction

Question 14

What is the maximum number of orders given by?

Answer 14

value of d/λ rounded down to nearest whole number

Question 15

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

Answer 15

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

Question 16

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

Answer 16

temperature of light source

Question 17

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

Answer 17

shorter the wavelength of brightest part of spectrum

Question 18

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

Answer 18

can measure temperature of light source

Question 19

Example of light sources that emit light at specific wavelengths?

Answer 19

glowing has in vapour lamp or discharge tube

Question 20

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

Answer 20

consists of narrow vertical lines of different colours

Question 21

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

Answer 21

characteristic of chemical element that produced the light

Question 22

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

Answer 22

elements in gas can be identified by observing its line spectrum

Question 23

What is a line absorption spectra?

Answer 23

continuous spectrum with narrow dark lines at certain wavelengths

Question 24

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

Answer 24

think dark vertical lines superimposed on continuous spectrum

Question 25

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

Answer 25

due to elements in glowing gas

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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