| Date | May 2012 | Marks available | 1 | Reference code | 12M.1.HL.TZ2.18 |
| Level | Higher level | Paper | Paper 1 | Time zone | Time zone 2 |
| Command term | Question number | 18 | Adapted from | N/A |
Question
A coherent beam of light of wavelength λ is incident on a double slit. The width of the slits is small compared to their separation. An interference pattern is observed on a distant screen. O is the mid point of the screen.
There is a bright fringe at O and a bright fringe at P. Between O and P there are three dark fringes.
Which of the following is the path difference between the light from the two slits arriving at P?
A. 1.5 λ
B. 2 λ
C. 3 λ
D. 4 λ
Markscheme
C
Examiners report
Young's double slit experiment is not explicitly on the syllabus. But candidates are expected to study the condition for constructive interference in terms of the path difference (4.5.6). This question was deemed fair and it was pleasing to see how many candidates chose the correct response.
