Physics of The Sun and Radiation

The Sun

• The Sun is a yellow dwarf star that is approximately 4.5 billion years old.
• It is a hot, glowing sphere composed primarily of hydrogen and helium.
• The Sun's radius is approximately 6.96 x 10^8 meters.
• Its surface temperature is around 5780 Kelvin.

Radiation

• Radiation is a form of energy that travels through space at the speed of light.
• A blackbody is a theoretical object that emits radiation at its maximum possible intensity for every wavelength.
• It absorbs all radiation that is incident upon it.
• Emissivity (ξ) is the ratio of a surface's radiation output to the radiation output of a blackbody at the same wavelength and temperature.
• A blackbody has an emissivity of 1.0.

Stefan-Boltzmann Law

• All objects with a temperature above absolute zero emit radiation.
• The rate of radiation emission is proportional to the fourth power of the object's absolute temperature.
• The formula for this relationship is E = σT^4, where:
  • E = total radiation emitted per square meter (W/m^2)
  • σ = Stefan-Boltzmann constant (5.67x10^-8 W/m^2-K^4)
  • T = temperature (K)

Wien's Displacement Law

• The higher the temperature of an object, the shorter the wavelengths of emitted radiation.
• As an object's temperature increases, the peak of its radiation emission shifts towards shorter wavelengths.
• The formula for this relationship is λmax = 2897 μm-K/T, where:
  • λmax = maximum wavelength (μm)
  • T = temperature (K)

Solar Constant

• The Solar Constant is the radiant flux density (RFD) reaching the Earth's atmosphere, measured on a surface perpendicular to the incoming radiation, when the Earth is at its mean distance from the Sun.

The Sun

• The sun, a yellow dwarf star, is approximately 4.5 billion years old.
• Composed of hydrogen and helium, the sun is a hot, glowing ball.
• The sun's radius is around 6.96 x 10^8 meters.
• The sun's surface temperature is approximately 5780 Kelvin.

Radiation

• Energy emitted from a source that travels through space at the speed of light.
• Blackbody:
  • Emits radiation at the maximum possible intensity for all wavelengths.
  • Absorbs all incident radiation.
  • A perfect emitter and absorber.
• Emissivity:
  • The ratio of a surface's or body's emittance to the emittance of a blackbody at a specific wavelength and temperature.
  • Emissivity of a blackbody is 1.0.

Stefan-Boltzmann Law

• All objects with a temperature above absolute zero emit radiation.
• Radiation emission rate is proportional to the fourth power of an object's absolute temperature.
• Equation:
  • E (total radiation emitted per square meter) = σ (Stefan-Boltzmann Constant) * T^4 (temperature in Kelvin)
  • σ = 5.67x10^-8 W/m^2-K^4

Wien's Displacement Law

• Higher object temperatures correlate with shorter emitted radiation wavelengths.
• As an object's temperature increases, its peak radiation emission shifts towards shorter wavelengths.
• Equation:
  • λmax (maximum wavelength in micrometers) = 2897 μm-K / T (temperature in Kelvin)

Solar Constant

• The radiant flux density at the top of Earth's atmosphere.
• It is measured on a surface perpendicular to the incident radiation.
• Measured when Earth is at its average distance from the sun.

Explore the fascinating characteristics of the Sun and the principles of radiation. This quiz delves into the Sun's composition, age, and temperature, along with the concepts of blackbody radiation and the Stefan-Boltzmann Law. Test your knowledge on these fundamental topics in physics.