1. 14.2 – NOTES Solar Radiation

2. The Earth’s atmosphere is needed for several reasons
Midday sun would fry eggs on rock
UV rays would burn skin
Nights would be cold enough to freeze CO2 into a solid, in the form of dry ice
Sun’s radiant energy and atmospheric gases make an hospitable climate
The atmosphere acts as a reservoir/storage unit for oxygen and carbon dioxide
It also protects us from harmful radiation and moderates temperature

3. B.1 The Electromagnetic Spectrum and Solar Radiation
Sun’s energy is a result of nuclear fusion
Fusion is combining 2 small nuclei into 1 larger nucleus
The reaction is extremely exothermic (releases a lot of energy)

4. Electromagnetic radiation
Energy liberated through fusion in the sun is transmitted to earth as electromagnetic radiation
Electromagnetic spectrum
Shows wavelengths and frequencies of various wave types, but all waves have the same speed
Type of ER represents a particular wavelength and frequency
Radio, micro, infrared, visible light, UV, x-rays, gamma rays, cosmic rays

6. Made of photons
Small packets of light that travel as waves
Photons transfer energy as they collide/interact with matter

7. Electromagnetic radiation travels as wave
Do not require a medium to travel through- can move through a vacuum as well as air
They oscillate, therefore have
Frequency- f – the number of waves that pass a given point per second, unit is Hertz (Hz)
Hertz – 1/s or s-1
Wavelength- l - distance between the top of two successive waves
C= l * f
C = speed of light = 3 x 108 m/s – all electromagnetic radiation moves at this speed
l = wavelength (m)
F = frequency (1/s)

8. Solar radiation
The radiant energy given off by the sun is spread over a large portion of the spectrum
The majority of the radiation falls in three regions
45% in IR region
46% in visible region
9% in UV region

9. Infrared radiation (IR)
Frequencies slightly lower than visible red light, and wavelength is slightly longer
Causes certain bonded atoms to vibrate more energetically, which increase the object’s temperature
Most is absorbed by CO2 and H2O in the atmosphere
This was demonstrated by Tyndall in 1860s
This process reradiates energy back into the atmosphere, where it is retained and helps to warm the atmosphere

10. Visible radiation
More than 90% reaches the surface on a clear day
Can energize electrons in some bonds
Interacts with electrons is chlorophyll molecules, which provides the energy needed for photosynthesis

11. Ultraviolet radiation
The most harmful radiation given off by the sun
Three separate categories
UV-A
Longest wavelength, lowest energy
Longer than 320 nm
Most absorbed by ozone layer
Effects: tanning, sunburn, DNA damage, skin cancer

12. UV-B nm
Most absorbed by stratospheric ozone layer
Effects: sunburns, skin cancer, DNA damage

13. UV-C
Most energetic of the three UV types
Blocked by the ozone layer
Wavelengths shorter than 280 nm
Have enough energy to break covalent bonds
Used to sterilize materials because it can kill bacteria and destroy viruses
Effects: DNA and tissue damage, kills bacteria and viruses

15. Humans need some UV radiation to produce vitamin D