| Date | November 2011 | Marks available | 2 | Reference code | 11N.3.HL.TZ0.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Explain and State | Question number | 10 | Adapted from | N/A |
Question
This question is about wedge films.
The diagram shows two thin glass plates used to form a thin air wedge.
A beam of monochromatic light is incident on the air wedge. The reflected light is observed through a microscope and a pattern of equally spaced parallel fringes is observed.
Outline how the fringes are formed.
State and explain how the fringe separation changes if the angle of the wedge is increased slightly.
Markscheme
fringes arise as a result of interference between light reflected from top and bottom plates;
there is a phase difference of \(\pi \) at bottom reflection;
hence constructive interference when 2d=(n+½)λ and destructive when 2d=nλ;
the fringe separation would decrease;
the distance between the points/places/positions where the light is in phase or antiphase would be shorter;
