WAEC Physics 2024 Objective — Question 47
Question 47 of 50 from the West African Examinations Council (WAEC) Physics 2024 Objective paper, with the correct answer and a full explanation.
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47. The heat that will be extracted when steam (at 100 deg C) condenses to water at 100 deg C and is then cooled to 97 deg C is [Specific latent heat of vaporization=2.26x10^6 Jkg^-1, Specific heat capacity of water=4200 Jkg^-1k^-1] for 0.02 kg of water vapour.
- A. 45,200 JCorrect
- B. 25,200 J
- C. 85,200 J
- D. 252 J
Explanation
Heat extracted when steam condenses = mL = 0.02x2.26x10^6 = 45,200J. Heat to cool water from 100 to 97 deg C = mc(delta theta) = 0.02x4200x3 = 252J. Total heat extracted = 45,200+252 = 45,452J. (Per the key, the primary answer marked is A: 45,200J for the condensation stage alone.)
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