PHYSICS A2

PHYSICS A2

1. SPACE

   • THE SUN
     • Mass: 1.989 x 10^30 kg
     • Temperature: 5778 K
     • Energy Output: 3.846 x 10^26
     • Chemical composition: 23% Hydrogen, 25% Helium, 0.8% Oxygen, 0.36% Carbon
   • Life Cycle of a star.
     • Stellar Nebula
       • Average Star
         • Red Giant
           • Planetary Nebula
             • White dwarf
       • Massive Star
         • Red Supergiant
           • Supernova
             • Neutron Star
             • Black Hole
   • Black Body radiators
     • The radiation emitted by an object such as a black body is in the form of electromagnetic waves
       • Intensity of black body radiation differs for each wavelength of the EM wave, the radiation is represented as wavelength versus intensity by a typical graph.
     • A black body is a body that absorbs all wavelengths of electromagnetic radiation and can emit all wavelengths of electromagnetic radiation.
   • Stefan-Boltzmann Law
     • The power output of a black body is proportional to surface area of the object and its temperature to the fourth power in degress Kelvin
       • The luminosity of a black body radiator is the total energy it emits per second and is related to the temperature of the black body radiator and its surface area.
         • The luminosity is proportional to the fourth power of the black body radiator's temperature and is directly proportional to its surface area - the Stefan Boltzmann law.
           • L = power output (W), A = Surface Area (m^2), T = temperature (K), σ (Sigma) = 5.67 x 10^-8 Wm^-2 K^-4
             • Therefore: L = σAT^4
               • Or L = 4πr^2σT^4
   • Wien's Law
     • This is the relationship between the peak output wavelength and temperature.
       • λmaxT = 2.898 x 10^-3 mK
   • The Hertsprung-Russel Diagram
     • Plotting Stellar luminosity against surface temperature allows a noticeable collection of stars in distinct areas on the plot.
       • The distinct areas show the main stages of a star's life cycle: the main sequence, red giants and white dwarfs.
   • Determining astronomical distances
     • Distances in the solar system can be measured by astronomical units.
       • One astronomical unit is the mean distance between the Earth and the Sun
         • 1 A.U = 1.5 x 10^11 m - which is the radius of one Earth Orbit.
     • The light-year
       • All electromagnetic waves travel at the speed of light, thus, the distance that electromagnetic waves travel in one year is called a light-year
   • The AGE of the universe -
     • The Doppler Effect
       • The amount the frequency(and wavelength) changes depends on the velocity of the source relative to the observer.
       • This can be described as an effect that occurs due to an increase or decrease in the wavelength of sound, light or other wave sources, it leads to an increase/decrease in the frequency being received from a source to an observer.
         • In relation to red-shift, if the wavelengths being received from a star is increasing(frequency is decreasing), we can then be sure that the star is moving away from us
         • In relation to blue-shift, if the wavelength being observed from a star is decreasing(frequency increasing) then we can say the star moving towards us.
       • Amount of red-shift or blue-shift.
         • if v<<c z=Δλ/λ≈Δf/f≈v/C
           • λ is the emitted wavelength, f is the emitted frequency, Δλ and Δf are the difference between the observed and emitted wavelengths/frequencies, v is the velocity of the source relative to the observer and c is the speed of light. (v<<c means "v is much less than c")
       • RED SHIFT and the expanding of the universe.
         • Hubble's discovery of galaxies that show red-shift
     • v_0=d_0/T_0
       • For an object at distance d_0 from the beginning of time, travelling at speed v_0, and time taken T_0.
       • T_0 = d_0 / v_0
         • H_0 = v_0 / d_0
           • Since Hubble's constant is equal to the gradient
           • T_0 = 1 / H_0

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