Temperature and Heat Exchange Flashcards
How is the zone of peak emission determined?
Substance’s temperature which is given by Wein’s Law.
What does Wein’s law state? What is its principle?
- The wavelength of a radiation body’s peak emissions is inversely proportional to its absolute temperature.
- Hotter a body, shorter the wavelength of that body’s peak emissions.
What is the typical range of a wavelength of a substance?
Between 0.2 to 5.6 micromillimeters.
What is the range of wavelength of the solar energy emitted by the sun? What is the wavelength of the maximum radiation output?
- 0.5 to 5 micromillimeters.
- 0.48 micromillimeters
What is the percentage value and wavelength range of UV value?
- 7 to 9%
- 0.001 to 0.39 micromillimeters
What is the percentage value and wavelength range of visible light?
- 45 to 47%
- 0.39 to 0.78 micromillimeters
What is the percentage value and wavelength range of near-infrared/infrared?
- 46% (combined)
- 0.78 to 4 micromillimeters (near infrared)
- 4 to 100 micromillimeters (infrared)
Define sky radiation
Radiation that reaches the earth after having been scattered by clouds and aerosols in the atmosphere.
Define global/total solar radiation
Total solar radiation received by the Earth is the sum of sky radiation and direct radiation, which is called global solar radiation.
How does the distance between the sun and the earth affect the amount of solar energy received by the Earth.
- Greater amount of solar energy received at all latitude increases when the Earth is closer to the sun.
- Less solar energy received at all latitudes when the Earth is further away from the sun
What affects the distance between the sun and the Earth?
What orbital cycle the Earth is currently in as the Earth’s orbit moves between highly elliptical and nearly circular in a cycle that lasts roughly 100,000 years.
In the Southern Hemisphere, what is it called when the Earth is furthest away from the sun? What is the distance and when does it occur?
- Aphelion
- 152 million km
- Occurs in July (winter)
In the Southern Hemisphere, what is it called when the Earth is closest to the sun? What is the distance and when does it occur?
- Perihelion
- 147 million km
- Occurs in December (summer)
How does the altitude of the sun affect the amount of solar energy received by the Earth?
- Earth is on an axial tilt of 23.5º, thus the latitude where solar input is perpendicular shifts north and south.
- Basically meaning that only one latitude on the Earth’s rotating surface can receive radiation at 90º, while all other latitudes receive it obliquely.
- Where the oblique angle is acute, the sun’s energy must travel a greater distance to reach the Earth’s surface.
When is the vertical sun at its most northern latitude?
June
When is the vertical sun at its most southern latitude?
December
What months receive greater solar radiation in the Northern Hemisphere?
Between the end of March and September
What months receive greater solar radiation in the Southern Hemisphere
Between the end of September and March
When does nil insolation occur at the poles?
During the polar winter months
When does constant insolation take place at the poles?
During the polar summer months
What is the maximum angular input at the poles? When does it occur?
20º in the middle of the summer polar period.
How does the length of day affect how much solar energy the Earth receives?
A greater length of day will result in greater radiation output as there is a greater amount of time for the sun to output solar radiation.
Where in the world is it that the number of hours of daylight equals dark hours?
Equatorial regions at 12 hours each.
Is daylight shorter than night in summer and vice versa in winter?
No, daylight is longer in summer.
When do the hours of daylight and dark equal each other all over the world occur? Specifically, what dates do these events occur?
- When the perpendicular sun is exactly over the geographical equator.
- Twice a year, on or about 22 March and 22 September. Known as the equinoxes
