Question

A rear window defroster in a certain car is made of 10 identical resistive strips, each of 8.00-12 resistance, connected as shown on the figure and powered by a 12.0-V car battery. It is installed on a 120cm x 60cm window, that is covered by a 0.500-mm thick layer of ice. How long would it take to have all the ice melted using the heat supplied by the defroster? Assume no heat is lost to the surroundings, and the ice/window is initially at 0°C. Density of ice is 917 kg/m3, and its latent heat of fusion is 335 J/g.

Answer 1

1.20m x 0o6m x orx10-3. As the volume of the given appratus will become V2 120cm x 60cm X0.500 mm m 0.36X10 As the ice i spreaders d over the dimension of 1200 120 cm x 60 cm over a thickness g 0.5oo mm latent heat of fustanie Now as L = 3355/ g. and the density of the ice is f = 917 kg/m3 As we know that Sam v M=&v = 9178 3:6*10-3x10-1 * 0.33012 kg 3 3.3012 Kgx10- to fure So heat required the ice will be E = L XM 2 3358 3:3012 × 103 x10-1 1105,902 XL0-18 118590.25

As we know by Joule's law of hearing H = I²RE Now the current will be v=lRnet strips. 7 = v Rast stripte R one strip No of strips in all strips are parallel Aso combination, so + +1 R, R RO - R net New R = R₂ = Rs = --2- Ru= 82 o Rust =0.82 10 Hence Rnet strips Now I : 12 0.8 A

AS R=0.8 P215A Now the heat produced by the current will provide energy to the ice to fuse. ECH so 11059022 (15) ²X.Qxt- &t= 10 614309 s. 10 f Ô 14.395 -la 6 14.395 or 10.2398333 min so time required to the full ice to fuse is 614.39 seconds or 10.239 833 minutes,