From the scattering of sunlight, J. J. Thomson calculated the classical radius o

Question

From the scattering of sunlight, J. J. Thomson calculated the classical radius of the electron as having the value 2.82 10-15 m. Sunlight with an intensity of 425 W/m2 falls on a disk with this radius. Assume light is a classical wave and the light striking the disk is completely absorbed. (a) Calculate the time interval required to accumulate 1.50 eV of energy. (days) (b) Explain how your result for part (a) compares with the observation that photoelectrons are emitted promptly (within 10-9 s).

Explanation / Answer

Total energy E = LA

= (425)(3.14)(2.82 * 10-15)^2

= 1.06 * 10-26 W

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The time t needed to accumulate 1.50 eV energy will be

t = 1.50 eV / (1.06 * 10-26)

= (1.50 * 1.6 * 10-19) / (1.06 * 10-26)

= 2.26 * 10^7 s

= 2.26 * 10^7 s * (1day / 24 * 60 * 60s)

= 262 days

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