9. The main problem that physicists had in understanding blackbody radiation bef

Question

9. The main problem that physicists had in understanding blackbody radiation before Planck's work was: A) Blackbody radiation came from objects that were not actually black. B) The classically predicted frequency spectrum showed an infinitely large peak at low frequencies. C) The classically predicted frequency spectrum showed an infinitely large peak at high frequencies D) The classically predicted frequency spectrum had a minimum intensity rather than a maximum as observed E) The classically predicted frequency spectrum has a maximum intensity that decreased with temperature, rather than increasing as observed

Explanation / Answer

10)

1 keV electron
= h/p ( is the wavelength, h is the planck's constant, p is the momentum)
Kinetic energy= K = p2 /2m (m is the mass)
p = (2mK)1/2 =( 2* mass of electron * kinetic energy)1/2 = ( 2* 9.1 x 10-31 * 1 x 103 * 1.6 x 10-19)1/2

* multiplied 1.6 x 10-19 with the energy because that is the conversion factor from eV to Joules
substituting p in = h/p
= 6.625 x 10-34 /( 2* 9.1 x 10-31 * 1 x 103 * 1.6 x 10-19)1/2 = 0.038 nm


1.0 keV photon

= h c / Eph = 6.625 x 10-34 x 3 x 108/(1.6 x 10-19 x 1 x 103) = 0.12 nm

1.0 keV neutron

We use the same substitution as we used in the electron problem, only replacing the mass of electron with that of neutron. mass of neutron = 1.67 x 10-27 kg

= 6.625 x 10-34 /( 2* 1.67 x 10-27 * 1 x 103 * 1.6 x 10-19)1/2 = 9.06 x 10-14 m

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