Question

Q3. A cube with side lengths of 2.91 cm is heated to a constant temperature of 720 ◦C at the focal point inside of a parabolic reflector. This has the effect of directing all of the cube’s radiant energy toward a 3.92 kg pack of ice that is initially at −19.0 ◦C. If the emissivity of the cube is 0.466, how long does it take for the ice to completely vaporize? Use the following numbers in your calculation:

• The specific heat capacity of ice is 2090 J/kg · ◦C.

• The latent heat of fusion is 334 kJ/kg

• The specific heat capacity of liquid water is 4186 J/kg · ◦C.

• The latent heat of vaporization is 2256 kJ/kg

• The Stefan-Boltzmann constant is 5.67 × 10−8 W/m2 · K

Hint: Assume that the only heat transfer is by radiant energy and assume that the system is thermally isolated from its surroundings. Use that fact to determine the heat that is delivered to the ice.

Answer 1