A square plate of dimension a × a makes an angle θ = π/4 with the x axis in its rest frame
(S) as shown in the figure.
It is moving with a speed \(v=\sqrt{\frac{2}{3}} c\ \) along the x axis with respect to an observer S' (where c is the speed of light in vacuum). The value of the interior angle ϕ indicated in the figure (which is obviously π/2 in the frame S), as measured in S' is
1
\(\frac{π}{3}\)
2
\(\frac{2 π}{3}\)
3
\(\frac{π}{6}\)
4
\(\frac{4 π}{3}\)