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Speed of Light Speed of Light
Electromagnetic Spectrum Electromagnetic Spectrum of Light
Speed of Sound Speed of Sound
Sonic Boom Sonic Boom

Speed of Light 

The formula to calculate the speed of light, c, is:

c = 300 000 / refractive index (km/s)



Refractive Indices of Common Mediums

Air @ 0�C	1.0000
Air @ 25�C	1.0003
Ice		1.3100
Water		1.3300
Glass		1.5000

Speed of Light in Common Mediums

Vacuum		300 000 km/s (precise value = 299 792 458m/s
Air @ 25�C 	300 000 km/s
Water 		225 000 km/sBack to top
Glass		200 000 km/s

Electromagnetic Spectrum of Light

Light travels in waves and the width of the wave (the wavelength) produces different ranges of light.

Region Wavelength Relative size Source
Gamma Rays < 0.01nm
(10-12)		 Atomic Nuclei Nuclear reactions in objects which are highly dense and energetic such as Black Hole
X-rays 0.01 - 10nm
(10-8 - 10-12)		 Atom Super-heated gas from exploding stars when temperatures are near millions of degrees
Ultraviolet 10 - 310nm Molecules Young hot stars
Visible 400 - 700nm Bacteria Sun
Infra-Red 710nm - 1�m Viruses Our bodies radiate with peek intensity of about 900nm at 37�C
Microwaves 1�m - 1mm sugar grain Mobile phones, microwave ovens
Radio > 1mm FM: 1m
AM: Xm		 Radio waves are found everywhere, most notably in background radiation of universe. Radio stations send electromagnetic radiation (radio waves) in patterns to our radio which in turn decodes this pattern and translates it to sound.
Note:
  • Number of waves that pass through a point in one second is called Frequency (measured in Hertz)
  • Wavelength is inversely proportional to the frequency; as wavelength decreases, frequency increases
  • v = l x n where:
    • v = velocity of wave
    • l = wavelength
    • n = frequency
  • Energy is directly proportional to the frequency of light; as frequency increases, energy emission increases

Speed of Sound 

The formula to calculate the speed of sound, v(sound), in air is:


v(sound) = 331.5 + (0.6 x Tc) m/s

where	Tc is temperature in air
	331.5 is speed of sound in Air at 0�C

Speed of Sound in Common Mediums

Air @ 25�C		346
Hydrogen		1339
Alcohol			1207
Water			1497
Glass			4540
Aluminium		5000
Iron			5200
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Sonic Boom

What is the sonic boom?

Sonic boom is the sound heard when an object travels faster than the speed of sound(supersonic versus subsonic which is slower).

How is the sonic boom produced?

Simply put, when an object (lets say an aeroplane) is travelling in air it produces sound waves like the waves produced by a boat in water. At subsonic speeds, the sound waves would travel ahead of the plane and you would hear the sound of the aeroplane emitted at the same time as you would see it.

However, when the plane is moving at speeds greater than 346 m/s, these sound waves lag behind accumulating into a cone-shape under intense pressure. When this pressure is released, the sonic boom becomes audible.
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