4. In the successful explanation of temperature dependence of specific heat capacity of solids. does the use of Planck's distribution signify involvement of particles? In what sense can the oscillations in solids be considered as particles? Do they participate in collisions, for example, as in Compton scattering? 5. Probability density and variance a) A classical bead is free to move and occupy any position on a semi-circular horizontal track of radius R with equal probability fre 0s 0 < n, and zero chewhere (Fig.HA#1.5). Find the probability density p(0) and sketch it. Also find the variance of the probability. b) Find and sketch the probability density of its x-position and the variance. Figure HA#1.5