Question

A flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal plane wave $E_x=36\sin (1.20\times {10}^{7}z+6\times {10}^{15}t)V/m$. The average intensity of the beam will be

• A. $0.86W/m^2$
• B. $1.72W/m^2$
• C. $3.44W/m^2$
• D. $6.88W/m^2$

Answer 1

Answer: (B)

$1.72W/m^2$

average intensity $I=\frac{{ϵ}_{o}c{E}_{rms}^2}{2}$

${ϵ}_o=8.85\times {10}^{-12}$

$c=3\times {10}^8$

$E_{rms}=36$

$I=\frac{8.85\times 3\times 36\times 36\times {10}^{-4}}{2}=1.72\frac{W}{m^2}$