To solve this problem it is necessary to take into account the concepts of Intensity as a function of Power and the definition of magnetic field.
The intensity depending on the power is defined as
[tex]I = \frac{P}{4\pi r^2},[/tex]
Where
P = Power
r = Radius
Replacing the values that we have,
[tex]I = \frac{60}{(4*\pi (0.7)^2)}[/tex]
[tex]I = 9.75 Watt/m^2[/tex]
The definition of intensity tells us that,
[tex]I = \frac{1}{2}\frac{B_o^2 c}{\mu}[/tex]
Where,
[tex]B_0 =[/tex]Magnetic field
[tex]\mu =[/tex] Permeability constant
c = Speed velocity
Then replacing with our values we have,
[tex]9.75 = \frac{Bo^2 (3*10^8)}{(4\pi*10^{-7})}[/tex]
Re-arrange to find the magnetic Field B_0
[tex]B_o = 2.86*10^{-7} T[/tex]
Therefore the amplitude of the magnetic field of this light is [tex]B_o = 2.86*10^{-7} T[/tex]
