The amplitude of magnetic field in a parallel beam of light of intensity 2.0 Wm^-2 is :

$1.3 \times 10^{-7} T$

Intensity of a wave = $\frac{\text { energy } / \text { time }}{\text { area }}=\frac{\text { power }}{\text { area }}$

or $\mathrm{I}=\mathrm{u}_{\mathrm{av}} \mathrm{c}=\frac{1}{2 \mu_0} \mathrm{~B}_0^2 \mathrm{c} \Rightarrow \mathrm{B}_0=\sqrt{\frac{2 \mu_0 \mathrm{I}}{\mathrm{c}}}$

$\mathrm{B}_0=\sqrt{\frac{2 \times\left(4 \pi \times 10^{-7}\right) \times 2}{3 \times 10^8}}=1.3 \times 10^{-7} T$