DP Physics (last assessment 2024)
Question 18M.3.SL.TZ1.9c.ii
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.3.SL.TZ1.9c.ii |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate | Question number | c.ii | Adapted from | N/A |
c.ii.
[Maximum mark: 3]
18M.3.SL.TZ1.9c.ii
A ray of light travelling in an optic fibre undergoes total internal reflection at point P.
The refractive index of the core is 1.56 and that of the cladding 1.34.
The input signal in the fibre has a power of 15.0 mW and the attenuation per unit length is 1.24 dB km–1.
(c.ii)
Calculate the power of the output signal after the signal has travelled a distance of 3.40 km in the fibre.
[3]
Markscheme
attenuation = –1.24 × 3.4 «= –4.216 dB»
–4.216 = 10 log
I = 5.68 «mW»
Need negative attenuation for MP1, may be shown in MP2.
For mp3 answer must be less than 15 mW (even with ECF) to earn mark.
Allow [3] for BCA.
[3 marks]
