A ray of light passing through a prism $\left(\mu =\sqrt[]{3}\right)$  surface minimum deviation. It is found that the angle of incidence is double the angle of refraction within the prism. Then, the angle of prism is________(in degrees).

At minimum deviation :

i = i'

r = r'

$r+r\text{'}=A\Rightarrow r=\frac{A}{2}$

Snell's law :

1 sin I = $\sqrt[]{3}sinr=\sqrt[]{3}sin\frac{i}{2}$ $\text{exception 25:}\text{exception 25:}\frac{}{}$

$\Rightarrow 2cos\frac{i}{2}=\sqrt[]{3}$

$\Rightarrow i=60°$

$\begin{array}{l}i=2r\Rightarrow r=30°\\ \Rightarrow A=60°\end{array}$