A light ray entering an optical fiber surrounded by air is first refracted and then reflected as shown in Figure 25.55. Show than if the fiber is made from crown glass, any incident ray will be totally internally reflected. Figure 25.55 A light ray enters the end of a fiber, the−surface of which is perpendicular to its sides. Examine the conditions under which it may be totally internally reflected.
A light ray entering an optical fiber surrounded by air is first refracted and then reflected as shown in Figure 25.55. Show than if the fiber is made from crown glass, any incident ray will be totally internally reflected. Figure 25.55 A light ray enters the end of a fiber, the−surface of which is perpendicular to its sides. Examine the conditions under which it may be totally internally reflected.
A light ray entering an optical fiber surrounded by air is first refracted and then reflected as shown in Figure 25.55. Show than if the fiber is made from crown glass, any incident ray will be totally internally reflected.
Figure 25.55 A light ray enters the end of a fiber, the−surface of which is perpendicular to its sides. Examine the conditions under which it may be totally internally reflected.
SECTION B
Answer ONLY TWO questions in Section B
[Expect to use one single-sided A4 page for each Section-B sub question.]
Question B1
Consider the line element
where w is a constant.
ds²=-dt²+e2wt dx²,
a) Determine the components of the metric and of the inverse metric.
[2 marks]
b) Determine the Christoffel symbols. [See the Appendix of this document.]
[10 marks]
c)
Write down the geodesic equations.
[5 marks]
d) Show that e2wt it is a constant of geodesic motion.
[4 marks]
e)
Solve the geodesic equations for null geodesics.
[4 marks]
Page 2
SECTION A
Answer ALL questions in Section A
[Expect to use one single-sided A4 page for each Section-A sub question.]
Question A1
SPA6308 (2024)
Consider Minkowski spacetime in Cartesian coordinates th
=
(t, x, y, z), such that
ds² = dt² + dx² + dy² + dz².
(a) Consider the vector with components V" = (1,-1,0,0). Determine V and V. V.
(b) Consider now the coordinate system x' (u, v, y, z) such that
u =t-x,
v=t+x.
[2 marks]
Write down the line element, the metric, the Christoffel symbols and the Riemann curvature
tensor in the new coordinates. [See the Appendix of this document.]
[5 marks]
(c) Determine V", that is, write the object in question A1.a in the coordinate system x'. Verify
explicitly that V. V is invariant under the coordinate transformation.
Question A2
[5 marks]
Suppose that A, is a covector field, and consider the object
Fv=AAμ.
(a) Show explicitly that F is a tensor, that is, show that it transforms appropriately under a
coordinate transformation.
[5 marks]
(b)…
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