When a beam of light goes from a denser medium $\left({\mu }_d\right)$ to a rarer medium $\left({\mu }_r\right)$, then it is generally observed that the magnitude of the angle of incidence is half that of the angle of refraction. Then the magnitude of incident angle will be- $($here $\left.\mu =\frac{{\mu }_d}{{\mu }_r}\right)$