A short magnetic needle is pivoted in a uniform magnetic field of induction $1T.$ Now, simultaneously another magnetic field of induction $\sqrt 3 T$ is applied at right angles to the first field; the needle deflects through an angle $\theta'$ whose value is :

Question

$$\begin {array} {1 1} (1)\;30^{\circ} & \quad (2)\;45^{\circ} \\ (3)\;90^{\circ} & \quad (4)\;60^{\circ}\end {array}$$