12.8: Problem set

1.Under daylight conditions, the human eye exhibits maximum sensitivity to light at a wavelength of 555 nm. At what temperature (K) would a blackbody emit light with a peak intensity at this wavelength?

2.The sun has a radius of approximately 6.96 x 10⁸ m and an average surface temperature of 5,780 K. Assume it has an emissivity of 0.990. What is the total radiant flux from the sun in W m^-2 and in W?

3.Imagine the Earth is on the surface of a sphere whose radius is equal to the sun-Earth distance, 1.50 x 10 ¹¹m. If the total radiant flux from the sun (W) calculated above is evenly distributed over the surface of that imaginary sphere, what is the average flux in W m-2? [websites]

4.Use the Hargreaves method to estimate monthly ET₀ for Arcadia, Oklahoma, USA in the year 2016, given the data below. Use a spreadsheet and report only the annual total (mm).Assuming a latent heat of vaporization of 2.465 MJ kg^-1, one MJ m^-2 is equivalent to 0.4057 mm of evaporated water.

Table 12-1. Extraterrestrial radiation (Ra), mean temperature (T),mean of daily maximum temperature (Tmax), and mean of daily minimum temperature (Tmin)near Arcadia, Oklahoma, USA in 2016. Raestimates obtained from www.nrel.gov/midc/solpos/solpos.htmland temperatures obtained from the Oklahoma Mesonet, Spencer site.

Month	Ra	Ra	Tmax	Tmin	t bar
	**sign**	**sign**	**sign**	**sign**	**sign**
Jan	210	563	9.52	-1.61	3.66
Feb	270	676	16.1	2.8	9.5
Mar	348	932	19.7	6.6	13.3
Apr	418	1083	22.9	10.5	16.7
May	465	1246	24.8	14.2	19.4
Jun	482	1250	31.7	20.8	26.0
Jul	471	1260	33.6	23.3	28.1
Aug	429	1150	32.9	21.7	26.7
Sep	367	950	30.4	18.1	23.6
Oct	290	778	30.4	13.8	19.9
Nov	223	578	20.0	7.6	13.6
Dec	192	514	9.94	-1.97	4.03

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