1 / 14

Recall that light is EM radiation and is therefore characterized by its wavelength.

The Nature of Blackbody Radiation. Recall that light is EM radiation and is therefore characterized by its wavelength. The Nature of Blackbody Radiation. Imagine we had the “perfect” emitter of EM radiation. We would call that a “Blackbody”.

aoife
Download Presentation

Recall that light is EM radiation and is therefore characterized by its wavelength.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Nature of Blackbody Radiation • Recall that light is EM radiation and is therefore characterized by its wavelength.

  2. The Nature of Blackbody Radiation • Imagine we had the “perfect” emitter of EM radiation. We would call that a “Blackbody”. • The Sun (and all stars) give off nearly every wavelength of EM radiation. • But what wavelength dominates????? During this Solar Eclipse (1991) you can see the Corona of the Sun. It is extends hundreds of thousands of Kilometers into space

  3. The Nature of Blackbody Radiation • The simplest and most common way to produce EM radiation is to heat up an object.

  4. The Nature of Blackbody Radiation • Lets consider the welder here. • As the temperature increases what can we say about ... • The color? • The amount of Heat?

  5. The Nature of Blackbody Radiation BLACKBODY CURVES HYPERLINK

  6. The Nature of Blackbody Radiation • The Blackbody curve for the Sun • When we compare the curve for a star to the curve of a blackbody at a given temp, we can in effect... Take the temperature of a star from millions/billions of miles away!!!

  7. (PSRT) Wien's Displacement Law • The equations that describe these curves are rather complicated. • However, we can deduce 2 useful expressions. The first one relates temperature to wavelength of maximum emission. • aka Wien’s Displacement Law

  8. (PSRT) Wien's Displacement Law • Example: Determine the Surface Temperature of the Sun. • Assume λmax is 500 nm

  9. Stefan - Boltzmann Law • Thought Experiment. Consider a hot metal rod and a burning match at the same temp. • Which gives off more energy??? • We must consider the amount of energy emitted per surface area. ENERGY FLUX

  10. Stefan - Boltzmann Law • The energy flux is just a fancy way of saying “The amount of energy emitted from 1m2of an object’s surface per second.” [J/m2/sec] or [W/m2] • So for the match and metal bar, which one has a higher energy flux? Neither. But clearly the match will not do as much damage to your skin. • So what’s the difference?

  11. Stefan - Boltzmann Law • In 1879, Josef Stefan showed that • Five years later Ludwig Boltzmann derived the coefficient that related the 2 quantities. • Recall Luminosity is the power output of a star. Therefore....

  12. Sample problem: F1 (c) M02 exam Antares A is part of a binary star system. The companion star Antares B has a surface temperature of 15 000 K and a luminosity that is 1/40 of that of Antares A. Calculate the ratio of the radius of Antares A to Antares B. Antares A has a surface temperature of 3000 K. This info was provided in an earlier part of the problem (not stated).In addition, you must know the formula for the surface area of a sphere to solve these types of problems.

  13. CLASSWORK • Worksheet on • Apparent Brightness • Wien’s Law • SB Law

More Related