| Date | November 2016 | Marks available | 2 | Reference code | 16N.3.SL.TZ0.14 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Explain | Question number | 14 | Adapted from | N/A |
Question
Optical fibres can be classified, based on the way the light travels through them, as single-mode or multimode fibres. Multimode fibres can be classified as step-index or graded-index fibres.
State the main physical difference between step-index and graded-index fibres.
Explain why graded-index fibres help reduce waveguide dispersion.
Markscheme
step-index fibres have constant «core» refracting index, graded index fibres have refracting index that reduces/decreases/gets smaller away from axis
OWTTE but refractive index is variable is not enough for the mark.
Award the mark if these ideas are evident in the answer to 14(b).
«in graded index fibres» rays travelling longer paths travel faster
so that rays travelling different paths arrive at same/similar time
Ignore statements about different colours/wavelengths.
