(a) Define specific latent heat of vaporization.
(b) (i) What are renewable energy sources?
(ii) List four renewable energy sources.
(c) Explain why tomatoes keep longer when kept in a moist jute bag in a clay pot.
(d) A box has a volume of 0.28 m\(^3\) and is 70% filled with iron fillings at 25^\circC. Calculate the:
(i) total mass of the iron fillings;
(ii) energy required to melt 10% of the iron fillings. [Density of iron = 8.00 x 10\(^3\) kgm\(^{-3}\); specific latent heat of fusion of iron = 1.38 x 10\(^5\) Jkg\(^{-1}\), specific heat capacity of iron = 460 Jkg\(^{-1}\) k\(^{-1}\), melting point of iron = 1500^\circC] 10.
Verified Correct Answer: .
Physical Principles & Numerical Solution
a) Specific latent heat of vaporization in the quantity of heat required to change a unit mass of a liquid at its boiling point to gas.
(b)(i) Renewable energy sources are sources of energy that cannot be exhausted.
(ii) Renewable energy sources are sun or solar, wave, wind, hydroelectric, tidal, biomass or vegetable oils, geothermal, etc.
(c) Clay pot is porous, therefore molecules of water in the moist jute bag will extract latent heat of vaporization from the tomatoes which will escape through the pores of the pot, thereby causing cooling of the tomatoes.
(i) Mass = density x volume = 8.00 x 10\(^3\) x \(\frac{70}{80}\) x 0.28 = 1568 kg.
(ii) Energy required Q = MC (\(\theta_2 - \theta_1\)) + mL
= \(\frac{10}{100}\) x 1568 x 460(1500 - 25) + \(\frac{10}{100}\) x 1568 x 1.38 x 10\(^5\)
= 106, 388, 800 + 21,638, 400
= 128,027,200J or 1.28 x 10\(^8\)J
Source: Myschool Past Questions Archive (Record #52989)