1.10 At some instant, a charge $q$ is observed to be at position $(x, y, z) = (a, 0, 0)$ and travelling in the negative $z$ direction with velocity $v$, in free space. Develop an expression for the magnetic field generated by this charge at the instant in question, at a point $P(x, y, z) = (0, b, 0)$ in terms of $q, a, b$ and $v$.