EATS 1011 Lecture 3

Energy

• Ability or capacity to do work
  
• Comes in many forms, kinetic, potential, heat, etc
  
• Energy is conserved
  
  • 1^st law of thermodynamics
    
• Work is done on matter if it is pushed, pulled or lifted over some distance
  
  • Example: lifting implies exerting force against gravity
    
• By doing work on something we give it energy which can be used to do work on something else
  
  • Example pulling a spring gives stored potential energy
    
• The energy stored in an object (internal energy) determines how much work it can do. This is called gravitational potential energy or potential energy à potential to do work
  
  • Example potential energy lifting a mass through a height
    
  • –PE = mgh
    
• Where
  
  • M = mass(kg)
    
  • G = gravitational acceleration(m/S²)
    
  • H = distance lifted (m)
    
• Unites of energy
  
  • 1 erg = 1 dyne/cm = 2.388 x 10^-8cal
    
• 1 joule (j) = 1 newton meter (N.m) = .239cal
  
  • =10⁷
    erg
    
• 1 calorie (cal) = 4.186 J = 4.186 * 10⁷ erg
  
• Chemical potential energy
  
  • A substance has potential energy if it can do work when a chemical change can occur (coal , natural gas, chemicals, food have PE)
    
• Kinetic energy (KE) = energy of motion
  
  • KE = ½ mv²
    
• Where:
  
  • M = mass(kg)
    
  • V = velocity (m/s)
    
• Faster moving à higher KE
  
  • Example strong wind has more KE
    
• Kinetic energy of random motion is often referred o as Heat Energy
  
• Energy can't be destroyed or created, it only moves from one form to another
  

Atmospheric Heating

• Conduction
  
  • Molecular motions
    
  • Near surface
    
  • Thermosphere
    
• Convection
  
  • Macroscopic motions
    
    • Example winds, turbulence
      
  • Horizontal, vertical
    
  • Hot air rises
    
    • Example a hot surface transferring hot surface energy into the atmosphere
      
    • 
      
• Latent heat
  
  • Condensation to evaporation
    
  • Freezing/fusion/melting
    
  • Sublimation
    
    • As water goes through the three phases energy about 1 million joules per kilogram of ice to have it turn to water
      
    • And 2.5 million joules for water to turn to vapour
      
• Radiation
  
  • Energy transfers at the speed of light
    

  Electromagnetic Radiation
  

  • EMR/ light has both wave and particle properties(photon)
    
  • λ -Wavelength(m)
    
  • v – frequency (s^-1)
    
  • C = λv = 3*10⁸m/s
    
    • The speed of light
      
  • E = hv(j)
    
    • H = 6.636*10^-34Js
      
  • "black body or planck Body: is a hypothetical body that emits radiation in a manner so that the total amount of en4ergy is only a function of temperature and spectral shape is a universal function with a single peak (see later) (P35)
    
  • The total amount of energy (integrate over v) crossing a square meter per second is given by Stefan-Boltzman Law
    
    • E(T) = λT⁴Wm^-2
      
    • Where λ = 5.67 * 10^-8 W m^-2K^-4 is the Stefan-Boltzman constant
      
  • The location of the peak is given by Wien's Law
    
  • 
    
  • Question: what is the wavelength of the maximum radiation emitted by the earth and by the sun?
    
    • for Eatrch the average surface temp is
      
      • 288Kelvin(15C)
        
    • For the sun
      
      • 6000 kelvin
        
      • Using wien's law we can find the wavelength of the maximum radiation
        
        • For earth λ_max ~ 10um mid-IR radiation
          
        • For te sun λ_max ~ .5um visible radiation
          

Solar Properties

• Main sequence star
  
• Burns H – fusion
  
• Layers
  
  • Core ~ 10⁷k
    
  • Radiative zone
    
  • Convective zone
    
  • Photosphere ~ 6000k (What we see)
    
  • Chromospheres ~ 4000k
    
  • Corona ~ 1 000 000k
    
  • Sun spots ("cold") prominences, granules, spicules, etc
    
  • R₀ ~ 700 000km
    
  • Emits L_(sun) = 3.9 * 10²⁶W
    
  • Spectrum ~ planck body = f(v,t) universal function
    
  • Use S-B equation give T_sun ~ 5700k (effective temperature)
    
  • Solar cycle ~ 11 years
    
  • Total output variation <.1% over 20 years
    
    • EUV > 3
      
    • X-Ray ~ 100
      
  • The more sunpots, the more energy from the sun
    

Which is interesting because the sun gives off most heat when it has the most spots with 'cold spots'