 Solution

ID: past-exam-of-the-physics-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2012/paper-1/section-a/a9/solution

ω^{2} = c^{2} [k_{g}^{2} + (π / a)^{2}]

f_{c} = c / (2 a) = 1.499 GHz

. In a lossless empty guide, energy travels at group velocity,

v_{E} = \frac{d ω}{d k _{g}} = c 1 - \frac{f _{c}^{2}}{f ^{2}} = 0.8003 c ≃ 2.40 \times 1 0^{8} m s^{- 1} .

ω / k_{g} = c^{2} / v_{E}

 New to topics? Read the docs here!