Date | May 2017 | Marks available | 2 | Reference code | 17M.2.SL.TZ1.2 |
Level | Standard level | Paper | Paper 2 | Time zone | 1 |
Command term | Describe | Question number | 2 | Adapted from | N/A |
Question
Outline what is meant by the principle of superposition of waves.
Red laser light is incident on a double slit with a slit separation of 0.35 mm.
A double-slit interference pattern is observed on a screen 2.4 m from the slits.
The distance between successive maxima on the screen is 4.7 mm.
Calculate the wavelength of the light. Give your answer to an appropriate number of significant figures.
Explain the change to the appearance of the interference pattern when the red-light laser is replaced by one that emits green light.
One of the slits is now covered.
Describe the appearance of the pattern on the screen.
Markscheme
when 2 waves meet the resultant displacement
is the «vector» sum of their individual displacements
Displacement should be mentioned at least once in MP 1 or 2.
λ =
= 6.9 x 10–7 «m»
answer to 2 SF
Allow missed powers of 10 for MP1.
green wavelength smaller than red
fringe separation / distance between maxima decreases
Allow ECF from MP1.
bright central maximum
subsidiary maxima «on either side»
the width of the central fringe is twice / larger than the width of the subsidiary/secondary fringes/maxima
OR
intensity of pattern is decreased
Allow marks from a suitably labelled intensity graph for single slit diffraction.