All Problems

Dispersion and Absorption of Light

Problem 5.200

A free electron is located in the field of a monochromatic light wave. The intensity of light is I=150 W/m2I=150 \mathrm{~W} / \mathrm{m}^{2}, its frequency is ω=3.41015 s1\omega=3.4 \cdot 10^{15} \mathrm{~s}^{-1}. Find: (a) the electron's oscillation amplitude and its velocity amplitude; (b) the ratio Fm/FeF_{m} / F_{e}, where FmF_{m} and FeF_{e} are the amplitudes of forces with which the magnetic and electric components of the light wave field act on the electron; demonstrate that that ratio is equal to 12v/c,\frac{1}{2} v / c, where vv is the electron's velocity amplitude and cc is the velocity of light.

Instruction. The action of the magnetic field component can be disregarded in the equation of motion of the electron since the calculations show it to be negligible.

Reveal Answer
5.200. (a) a=eE0/mω2=51018 cm,a=e E_{0} / m \omega^{2}=5 \cdot 10^{-18} \mathrm{~cm}, where E0=2I/ε0c,v=E_{0}=\sqrt{2 I / \varepsilon_{0} c}, \quad v= =aω=1.7 cm/s=a \omega=1.7 \mathrm{~cm} / \mathrm{s} (b) Fm/Fe=2.91011F_{m} / F_{e}=2.9 \cdot 10^{-11}