Assume that a 110 W light bulb radiates all its energy as a single wavelength of

Question

Assume that a 110 W light bulb radiates all its energy as a single wavelength of visible light. Estimate the electric field strength at the surface of the bulb. Assume that the bulb is a sphere and its radius is 2.8 cm. Estimate the magnetic field strength at the surface of the bulb.

Explanation / Answer

Assuming E varies sinusoidally. The average power/unit area of the electromagnetic beam at the surface of the bulb where Eo and Bo are the peak amplitudes is: Po / area = Eo^2 / (2*c*uo) = 130 watts/m^2 Surface area of bulb: 4*pi*r^2 Po / area = Eo^2 / (2*c*uo) = 130 / 4*pi*r^2 =130 / (4*3.14159*0.028^2) = 13195 watts/m^2 --->at radius r Eo^2 / (2*c*uo) = 13195 Solving for Eo Eo = sqr(2*3*10^8*(4*3.14159*10^-7)*13195) = 3154.17 N/c "peak" Since Eo = c*Bo Bo = 3154.17/(3*10^8) = 0.0000105139 T "peak" For rms values: divide Eo or Bo by sqr(2)

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