91影视

The expression for the intensity radiated by sun in terms of electric field is$\mathbf{I}\mathbf{=}\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{蔚}}_{\mathbf{0}}{\mathbf{c}{\mathbf{E}}_{\mathbf{m}\mathbf{a}\mathbf{x}}}^{\mathbf{2}}$Emax is the maximum value of electric field in the sinusoidal wave,${\mathbf{蔚}}_{\mathbf{0}}$is the permittivity in the vacuum, c is the speed of light.

Refer equation $\mathrm{I}=\frac{1}{2}{\mathrm{蔚}}_0{{\mathrm{cE}}_{\max }}^2$The speed of light and the permittivity in the vacuum is constant for vacuum.

Figure I

The graph is draw between the intensity radiated by sun and the square of the maximum electric field. Thus, the intensity is directly proportional to the square of the maximum electric field and it is depends only on electric field.

$\mathrm{I}鈭�{{\mathrm{E}}_{\max }}^2$and can be concluded asthe intensity increases square of the electric field also increases.

Therefore, the graph should be a straight line and the slope is equal to$\frac{1}{2}{\mathrm{蔚}}_0\mathrm{c}$

The best fit straight line has a slope$1.33脳{10}^{-3}\mathrm{J}/{\mathrm{V}}^2\mathrm{s}$

Refer part (a), the slope of the straight line is$\frac{1}{2}{\mathrm{蔚}}_0\mathrm{c}$.Thus,

$\frac{1}{2}{\mathrm{蔚}}_0\mathrm{c}=1.33脳{10}^{-3}\mathrm{J}/{\mathrm{V}}^2\mathrm{s}$

Rearrange the equation to find the speed of light in air, is

$$\begin{gathered} {\mathrm{蔚}}_0\mathrm{c}=1.33脳{10}^{-3}\mathrm{J}/{\mathrm{V}}^2\mathrm{s}脳2 \\ \mathrm{c}=\frac{2.66脳{10}^{=3}\mathrm{J}/{\mathrm{V}}^2\mathrm{s}}{{\mathrm{蔚}}_0} \\ =\frac{2.66脳{10}^{-3}\mathrm{J}/{\mathrm{V}}^2\mathrm{s}}{8.854脳{10}^{-12}{\mathrm{C}}^2/{\mathrm{Nm}}^2} \\ =3.00脳{10}^8\mathrm{m}/\mathrm{s} \end{gathered}$$

Therefore, the speed of light in the air is $3.00脳{10}^8\mathrm{m}/\mathrm{s}$