5.2 Lab: Optics 1

Part 1: Blackbody Radiation and the Greenhouse Effect
Much of the light we see comes from atoms and molecules, which are so hot they vibrate and collide with high-energy motion. Every time an atom changes the direction it is moving, the acceleration of electrons at the exterior of the atom causes light to be emitted. Objects at temperatures like the surface of the sun emit light in the visible part of the spectrum.

For a better understanding of what blackbody radiation is, read section 8.6 of the textbook (pp. 310–313), paying particular attention to the formula for the wavelength that is given the maximum power (p. 311) and example 8.4 which uses it.

Formulas for calculating these values can be found following the instructions for the other trials (page 12–13). Check your measurements with the spreadsheet available for download on Canvas. Measured values should be within about 5 cm of the calculated value. Do not use the calculated values to fill the table above. All numbers should come from the ruler measurements in the simulation.

To explain the relation between the blackbody spectrum and temperature (which remember is related to the amount of internal energy in a body), the energy of light had to be quantized using the equation: E=hf. This led to the recognition that while light is a wave it also has properties similar to particles. A particle of light is called a photon and it is localized in space as it moves at the speed of light (3×10^8 m/s).
The letter h stands for Planck’s Constant and is a fixed number given as 6.63×10^(-34 ) J/Hz or sometimes given with the unit Js. This is the energy in Joules of a photon with a frequency of 1 Hz. Higher frequencies have proportionately higher energies.

Trial 2: Move the object until the image and the object are the same distance from the mirror. Measure and record the values in the trial 2 column above.

Trial 3: Move the object so the image is taller than the object. Click on the icon showing a magnifying glass with a “–” sign in it to reduce the scale of the simulation view. Be careful reading the rulers. The ruler scale changes, so each tick-mark is 4 cm, not 2 cm as before. Record your values in the trial 3 column above.