Question

The sodium lamp used in a physics laboratory gives out light uniformly. Suppose
that the lamp uses 40 W. Calculate the magnitude of electric field.

Answer 1

Answer on Question #65051, Physics / Optics

The sodium lamp used in a physics laboratory gives out light uniformly. Suppose that the lamp uses 40 W. Calculate the magnitude of electric field.

Find: E - ?

Given:

P=40 W

$c = 3 \times 10^{8} \mathrm{~m/s}$

$\varepsilon_0 = 8.85 \times 10^{-12} \mathrm{~F/m}$

$\varepsilon = 1$

Solution:

Power of electromagnetic radiation:

P = wc (1),

where w is energy density, c is speed of light in vacuum.

Energy density:

$w = \varepsilon_0 \varepsilon E^2$ (2),

where $\varepsilon_0$ is electric constant, $\varepsilon$ is dielectric constant of the medium, E is magnitude of electric field.

(2) in (1):

P = $\varepsilon_0 \varepsilon E^2 c$ (3)

Of (3) $\Rightarrow E = \sqrt{\frac{P}{\varepsilon_0 \varepsilon c}}$ (4)

Of (4) $\Rightarrow E = 123 \mathrm{~V/m}$

Answer:

123 V/m

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