Older freezers developed a coating of ice inside that had to be melted periodica

Question

Older freezers developed a coating of ice inside that had to be melted periodically; an electric heater could speed this defrosting process. Suppose you're melting ice from your freezer using a heating wire that carries a current of 3.8A when connected to 120V. A. What is the resistance of the wire? (Answer in 2 significant figures and appropriate units) B. How long will it take the heater to melt 780g of accumulated ice at -10 degrees Celsius? Assume that all of the heat goes into warming and melting the ice, and that the melt water runs out and doesn't warm further. (Answer in 2 significant figures and appropriate units)

Explanation / Answer

The mass of the ice is m = 780g = 0.78 kg


the initial temperature Ti = -10C


then the amnount of heatrequired to the ice is Q = ms?T + mL

= (0.78kg) [ (2090 J/kg C) (10) + 3.33*10^5 J/kg] = 276042 J To supply this much of energy Q = I^2 Rt = I^2 (V/I) t = VI t The curent through the wire I = 3.8A the supplied voltage V = 120V

Q = (120) (3.8) t therefore the time t = 276042 / 456 = 605.3552631578947sec or

= 10.08925438596491min

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