AST- 105 1st EditionLecture 4Outline of Last LectureI. WavesII. SpectraIII. PhotonsOutline of Current LectureI. Heat and RadiationII. Temperature ScalesIII. Black Body RadiationCurrent LectureI. Heat and Radiationa. All objects absorb and emit EM radiation.i. Hotter objects emit more radiation than cooler objects of the same size.ii. The hotter the object, the more energetic the typical photon emitted. b. The color of a hot objectFa shifts from red to blue with increasing temperature. c. Infrared radiation does not pass through a clear lense (like eyeglasses). This is why sunglasses have to be tinted darker to shield us from the light of the sun.d. Energy travels through space as an IR electromagnetic wave.II. Temperature Scalesa. Fahrenheit- used in the USAi. Absolute Zero is found at -460 degreesii. Water freezes at 32 degreesiii. Water boils at 212 degreesb. Celsius- used outside the USA and in sciencei. Absolute Zero is found at -273 degreesii. Water freezes at 0 degreesiii. Water boils at 100 degreesc. Kelvin- absolute scale used in sciencei. K = C + 273ii. Zero K = Absolute Zeroiii. Water freezes at 273 degreesiv. Water boils at 373 degreesIII. Black Body Radiationa. Black Body- a term for an ideal absorber and emitter of EM radiationi. Examples include a heated bar of iron or a stellar photosphereb. Black Body Curve- plot of intensity vs. wavelength for black body of a given temperature T.i. max = wavelength of peak emission.1. Remember, is the symbol for lambda (see Lecture 3). c. Wien’s Law- max = const./ T with T in Kelvini. max decreases as T increases.1. This shows us that the hotter the Black Body, the more the peak shifts towards the blue color.2. At any , a hotter Black Body has a larger
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