The magnetic field in a plane electromagnetic wave travelling in glass ( n =1 · 5) is given by B_y =(2 × 10^-7 T ) sin (α x +1 · 5 × 10^11 t ) where…

The magnetic field in a plane electromagnetic wave travelling in glass $\displaystyle (\mathrm{n}=1 \cdot 5)$ is given by \[\mathrm{B}_{\mathrm{y}}=\left(2 \times 10^{-7} \mathrm{~T}\right) \sin \left(\alpha \mathrm{x}+1 \cdot 5 \times 10^{11} \mathrm{t}\right) \] where x is in metres and t is in seconds. The value of $\displaystyle \alpha$ is :