In: Physics
An optical interferometer can detect a displacement of 0.1?, or ?50nm.
At what speed would a 3.0m stick "shrink" by 50 nm? Hint: Use the binomial approximation.
Length contraction is governed by equation
L = L0 * v (1 - v2 / c2)
hence change in length delta L = L0 - L
= L0 * [1 - v (1 - v_2 / c_2) ] ----- (1)
v (1 - v^2 / c_2) = (1 - x) /2 ( where x = v^2 / c_2, )
= (1 - x/2)
= 1 - v^2 / 2c_2
delta L = L_0 * [ 1 - 1 + v^2 / 2 * c_ 2 ]
50 * 10-9m = 3.0 * v^2 / 2 * c_2
v^2 = 50 * 10-9 * 2 * c2 / 3.0
= sqrt (3.33 * 10-8 ) * c2
v = 1.83 * 10-4 m/s * 3.00 * 108 m/s
= 5.49 * 104 m/s