When a metal is heated its density decreases. there are two sources that give rise to this decrease of rho: (1) the thermal expansion of the solid and (2) the formation of vacancies (section 5.2). consider a specimen of gold at room temperature (20°c) that has a density of 19.320 g/cm3 . (a) determine its density upon heating to 800°c when only thermal expansion is considered. (b) repeat the calculation when the introduction of vacancies is taken into account. assume that the energy of vacancy formation is 0.98 ev/atom, and that the volume coefficient of thermal expansion, αv is equal to 3αl .

The heater element of a 120 v toaster is a 5.4 m length of nichrome wire, whose diameter is 0.48 mm. the resistivity of nichrome at the operating temperature of the toaster is 1.3 × 10-6 ω·m. the toaster is operated at a voltage of 120 v. (a) what is the power drawn by the toaster? (b) if the cost of electricity is 12 ¢ per kilowatt-hour, and it takes 2 minutes to toast bread, how much does it cost for toasted bread? (c) when the heater element is at room temperature, is the resistivity in the nichrome wire greater than, less than, or equal to it’s resistivity when at operating temperature? explain.