3.4 Diffraction

Question 1

What is diffraction?

Answer 1

• spreading out of waves when they pass an obstruction
• obstruction being a narrow slit

Question 2

What is the extent of diffraction dependent on>

Answer 2

• the width of the gap compared with the wavelength of the waves

Question 3

What is refraction represented by?

Answer 3

• a wavefront with vertical lines going through a straight lines materiel with a slit
• then the diffracting wave shown as semicircle;es increasing in circumference

Question 4

How is the diffraction patter of light represented?

Answer 4

• as a series of light and dark fringes which show the areas of maximum and minimum intensity

Question 5

What are the features of the single slit diffraction patter?

Answer 5

• a central maximum with a high intensity
• Subsidiary maxima equally spaced, successively smaller in intensity and half the width of the central maximum

Question 6

What would occur if the laser were to be replaced by a non laser source emitting white late?

Answer 6

• central max is white
• all maxima would be from a spectrum
• shortest wavelength closest to central max and longer is further away
• colours more blurry further away
• maxima move further away
• fringe spacing would be smaller and non central maxima is wider

Question 7

What is a diffraction grating?

Answer 7

a plate on which there is a very large number of parallel, identical, close spaced slits

Question 8

What occurs when monochromatic light is incident on a grating?

Answer 8

• a pattern of narrow bright fringes is produced on a screen
• the angles the maxima of energy are produced can be deduced by the diffraction grating equation

Question 9

what are 2 applications of diffraction grating?

Answer 9

• separating light of different wavelengths with high resolution
• used in spectrometers
• play a role in x-ray crystallography

Question 10

How are diffraction gratings used in spectrometers?

Answer 10

• analyse light from stars
• analyse composition of a star
• chemical analysis
• redshift/rotation of a star
• wavelength/frequency of light
• observed spectra if meterials
• absoprtion / emission spectra in stars

Question 11

How does diffraction grating play a role in x-ray crystallography?

Answer 11

• X-rays are directed at a thin crystal sheet which acts as a diffraction grating to form a diffraction pattern
• this is because the wavelength of X-rays is similar in size to the gaps between the atoms
• the patterns can be used to measure the atomic spacing in certain materials