Page 309 - General Knowledge

GENERAL KNOWLEDGE 2019

 Gamma rays have the smallest wavelengths and radio waves have the longest.
 Since light is a wave, we know that its speed must be equal to its frequency multiplied by its
wavelength.
 In other words,

 Here are the different types of waves with a general description of their uses and
characteristics.
Infrared
 Infrared electromagnetic waves are radiant heat.
 They are often referred as IR.
 We get a great deal of energy from the sun in the form of infrared waves.
 When you go out on the first warm spring day and bask in the sun, absorbing all that
wonderful heat, you are taking on infrared electromagnetic waves.

Visible light
 Visible light is important to us because we make great use of it to create mind pictures of our
surroundings.
 We arbitrarily arrange light into colors.

 The main colors, when we think of colors, are red, orange, yellow, green, blue, and violet.
 The colors are listed in iscreasing order of frequency.
 So red light photons have less energy than blue light photons.
 Commit to memory the energy order of visible light.
 So in order of increasing energy: red, orange, yellow, green, blue and violet.
 Ultraviolet (UV) light is a type of electromagnetic radiation that is all around us even though
our eyes can't detect it.
 Our bodies use it to make vitamin D, but too much exposure can cause painful burns and
even cancer.
 Although UV light can be dangerous, it is also very valuable and is used in many ways.
 UV light is used to identify biological materials, like blood, at crime scenes and in places
where sanitation is important. Because it can kill viruses and bacteria, it is also used to
sterilize medical and biological research facilities and to sanitize much of our food and water.

Types and Sources of UV light
 The UV spectrum is divided into vacuum UV (40-190 nm), far UV (190-220 nm), UVC (220-
290 nm), UVB (290-320 nm), and UVA (320-400 nm).
 The highest energy forms of UV light (Vacuum UV, Far UV, and UVC) are almost completely
absorbed by the Earth's atmosphere in the ozone layer.
 UVA is the most commonly encountered types of UV light and also the least harmful.
 UVA exposure causing tanning of the skin initially, followed by sunburn after prolonged
exposure.
 Ozone in the atmosphere absorbs very little UVA radiation, and it is present even on cloudy
days.
 UVA is also needed by humans for synthesis of vitamin D.

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