a) The light from a 200-W lamp spreads uniformly in all directions. Assuming that 5% of the lamp power is converted to light, find the irradiance of the optical E&M wave and the amplitude of the electric field at a distance of 10m from the lamp.
b) Suppose now a 2000-W laser beam is concentrated by a lens into a cross-sectional area of 10^-6 cm^2. Find the corresponding irradiance and amplitude of the E-field and B-field.