Atmosphere Contents

2. Solar Energy

Conclusion

The main source of radiation and the only external input to the Earth is from the sun. This solar radiation provides energy for the biosphere, atmospheric and oceanic circulation patterns and the weather systems. We can see only a small part of solar radiation - visible light. There is however a whole spectrum of light ranging from infrared radiation to ultraviolet radiation. Only 45% of the incoming radiation reaches the surface of the Earth, with 25% being reflected back into space by clouds and 25% being absorbed in the atmosphere. Radiation is extremely harmful to life and biological tissues and various processes in the atmosphere actually take out this potentially harmful ultraviolet radiation.

Questions and answers

1. How far is the sun from the Earth?

question 1 answers

2. What powers the sun and what is the average temperature of the photosphere?

question 2 answers

3. What are the crucial roles that solar radiation plays for life on Earth?

question 3 answers

4. What are the two theories of radiation?

question 4 answers

5. What are the four major regions of the radiation spectrum; and at what wavelength does visible radiation occur (i.e. stimulates the colour cones in the retina of the human eye)?

question 5 answers

6. What is i) the equation describing the energy of radiation at various wave lengths and ii) the energy for radiation of wavelength lambda = 700nm in the infra-red part of the spectrum?

question 6 answers

7. How much of the sun's radiation reaches the surface of the Earth and in what wavelengths does this predominantly occur?

question 7 answers

8. What are the first and second Laws of Thermodynamics?

question 8 answers

Question 1 answer

94 million miles

Question 2 answer

The sun is powered by thermonuclear reactions, the energy output of which appears as radiation. The average temperature of the photosphere is 6000 C.

Question 3 answer

Solar radiation provides the necessary energy for the existence of the biosphere, drives the atmospheric and oceanic circulation patterns, and powers the weather machine.

Question 4 answer

(i) The wave theory: oscillating electric field.

(ii) The photon theory:radiation is regarded as a stream of small packages of energy (known as photons). The wave theory is conventionally used to describe radiation quantitatively.

Question 5 answer

X-ray - UV - Visible - Infrared.

The wavelength of visible light extends roughly from about 400 nanometres (nm) (violet) to 700nm (red).

Question 6 answer

i) e =hc/lambda.
ii) e=hc/lambda = (6.625x 10E(-34) Joule seconds x 2.998 x 10E8 metres per second)/ 700 X 10E-9 metres = 2.84 X 10E-19 Joules

Question 7 answer

Only approximately 45% of the incoming radiation actually reaches the surface of the Earth. This is predominantly in the visible wavelength. About 25% is reflected into space by clouds and the remaining 25% is absorbed in the atmosphere by ozone, water vapour and carbon dioxide.

Question 8 answer

The first Law of Thermodynamics states that energy can neither be created nor destroyed, i.e. only transformed from one form to another. The second Law of Thermodynamics states that entropy (the disorder of a system) will never decrease as isolated systems will tend to thermodynamic equilibrium (objects tend to the same temperature) -- the state of maximum entropy.