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(a) Cherry-red embers in a fireplace are at $850^\circ\textrm{C}$ and have an exposed area of 0.200 m2 and an emissivity of 0.980. The surrounding room has a temperature of $18.0^\circ\textrm{C}$. If 50% of the radiant energy enters the room, what is the net rate of radiant heat transfer in kilowatts? (b) Does your answer support the contention that most of the heat transfer into a room by a fireplace comes from infrared radiation?
1. $8.80\times 10^{3}\textrm{ W}$
2. Compare to conduction: if we assume that heat conducted 1 meter away from the coals will reach beyond the fireplace, and therefore enter the room rather than go up the chimney, then only 3.83 W would be conducted to the room. Radiation has a heat transfer rate that is greater than that by conduction by a factor of 2300.
Solution Video

# OpenStax College Physics for AP® Courses Solution, Chapter 14, Problem 56 (Problems & Exercises) (2:38) Rating

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