Problem 2.

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Homework # 1, Electrodynamics 2: 7110. Due Wednesday, Sep 11. Problem 1. [4 points] Exercise 1.11 from the Brau's textbook (Doppler effect). Problem 2.
Homework # 2, Electrodynamics 2: 7110 Due Wednesday, Sep 9

Problem 1.

[4 points] Using the fact that k α = (ω/c, k) is a 4-vector (a photon

4-wavevector), apply the Lorentz transformation to this quantity to derive the Doppler shift for a light wave, that is, the frequency observed in the laboratory for a source moving in the x-direction with velocity v = βc for arbitrary k. The frequency of the photon in the rest frame of the source is ω0 , and θ is the angle of propagation in the laboratory frame of reference.

Problem 2. [3 points] Show that the result of two consecutive Lorentz transformations, see Eq. (1.67), with velocities V1 and V2 is equivalent to a single Lorentz transformation to a frame moving with some velocity V12 . Find that velocity assuming that V1 and V2 are pointed along the same direction.

Problem 3. [3 points] Two rods (each of length l0 in its own rest frame) are moving with velocities v towards each other in the laboratory reference frame. What is the length of each rod as measured in the reference frame of another rod?

Problem 4. [3 points] Consider two vectors Aα = (2, 2, 0, 0) and B α = (2, 1, 0, 0) in the reference frame K. Using the direct Lorentz transformation to a reference frame K ′ moving with velocity V = cβ in the positive direction of the x-axis show that a) the product Aα Bα is a scalar (invariant under the Lorentz transformation); b) the object A0 B 0 + A1 B 1 is not a scalar.

Problem 5. [2 points] Write the Lorentz transformations from frame K ′ to frame K for an arbitrary contravariant 4-vector Aα = (A0 , A) and arbitrary velocity V of the K ′ frame.