Photoelectric Effect Experiment
The Photoelectric Effect System is used to perform the photoelectric experiment, determining Planck’s Constant to within 5%. This apparatus uses the conventional method of determining Planck’s Constant. The metal plate in the photodiode is illuminated with various frequencies of light, selected from a mercury lamp using filters. The voltage is then adjusted to stop the photoelectric current. The stopping voltage is plotted vs. the frequency, and Planck’s Constant is determined from the slope of the graph.
The concept that the stopping voltage does not change with light intensity is tested using the various apertures that change the light intensity by partially blocking the light.
As early as 1914, James Franck and Gustav Hertz discovered in the course of their investigations an energy loss in distinct steps for electrons passing through mercury vapor and a corresponding emission at the ultraviolet line (λ= 254 nm) of mercury. They performed this experiment that has become one of the classic demonstrations of the quantization of atomic energy levels. They were awarded the Nobel Prize for this work in 1925.
PASCO Advantage: The advantage of using Capstone is that students are able to get many more data points compared to manually taking readings from the digital readouts. The peaks and troughs are easily measured using the coordinate tool.
Speed of Light Experiment
The Speed of Light Experiment uses laser light and a high speed rotating mirror to determine this fundamental constant using the Foucault method.
Laser light passes through a series of lenses to produce an image of the light source at a measured position. The light is then directed to a rotating mirror, which reflects the light to a fixed mirror at a known distance from the rotating mirror. The laser light is reflected back through its original path and a new image is formed at a slightly different position. The difference between final/initial positions, angular velocity of the rotating mirror, and distance traveled by the light are then used to calculate the speed of light in air.
PASCO Advantage: PASCO’s Speed of Light Experiment allows students to experimentally measure the speed of light within 5% of the accepted value. In addition, the experiment can be performed on a desktop or in a hallway.
Blackbody Radiation Experiment
In this experiment designed for use with PASCO Capstone software, the classic blackbody spectrum of light intensity versus wavelength is obtained for a light bulb and the shift in the peak wavelength is demonstrated for different bulb temperatures.
The spectrum of an incandescent light bulb is scanned by hand using a prism spectrophotometer, which measures relative light intensity as a function of angle. A Broad Spectrum Light Sensor is used with a prism so the entire spectrum from approximately 400 nm to 2500 nm can be scanned without the overlapping orders caused by a grating. The wavelengths corresponding to the angles are calculated using the equations for a prism spectrophotometer. The relative light intensity can then be plotted as a function of wavelength as the spectrum is scanned, resulting in the characteristic blackbody curve. The intensity of the light bulb is reduced, reducing the temperature, and the scan is repeated to show how the curves nest with a shift in the peak wavelength.
The temperature of the bulb’s filament can then be measured indirectly by determining the resistance of the bulb from the measured voltage and current. From the temperature, the theoretical peak wavelength can be calculated and compared to the measured peak wavelength.
PASCO Advantage: The light bulb is powered by the interface, making it easy to change its temperature by changing the voltage across the bulb. All the complex calculations for the angle-to-wavelength conversion are stored in the setup file for PASCO Capstone.
Wireless Diffraction System
The Wireless Diffraction System with Track contains all the equipment you need to perform labs and lecture demonstrations on Interference and Diffraction. This complete system includes the PASCO Diffraction Scanner combines a position sensor with a light sensor for scanning diffraction patterns. An included aperture setting allows for the adjustment of width-measurement resolution (and light attenuation). A hand crank allows for smooth scanning of diffraction patterns. Because of the wireless design, smooth scans are achieved effortlessly! This system enables students to scan many diffraction and interference patterns during one lab period. They can study the differences caused by changing the slit width, slit separation, and number of slits. And, by comparing patterns created by a Red Diode Laser to those of a Green Diode Laser, they can study the difference caused by a change in wavelength.
The large 3 cm wavelength makes it easy to understand and visualize electromagnetic wave interactions. Interference and diffraction slits are several centimeters wide, and polarizers are slotted sheets of stainless steel.
The heart of the Microwave Optics System is the Gunn Diode Transmitter and receiver. The transmitter is a low-voltage source of linearly polarized microwaves (10.5 GHz, 15 mW). The receiver has a built-in amplifier, as well as a variable sensitivity scale, ensuring accurate data for even the lowest intensity measurements.
No study of interferometry should overlook the historical importance of the Michelson interferometer. Yet in the laboratory, the Fabry-Perot and Twyman-Green interferometers can be more important tools; the first for high-resolution spectroscopy, the second for testing and producing optical components with aberrations that can be measured in fractions of a wavelength.
The PASCO Interferometer is a high-precision, movable-mirror interferometer that can be used to perform Michelson, Fabry-Perot and Twyman-Green interferometry. Mirrors are attached with thumbscrews, so it’s easy to set up and change configurations.
The PASCO Interferometer can be ordered in a variety of systems. The OS-9255A Basic Interferometer can be operated in either the Michelson or Fabry-Perot modes. The Complete Interferometer Systems also contain components for the Twyman-Green mode and a vacuum pump for the refractive index of air experiment.
Zeeman Effect Experiment
In this experiment the student observes the interference pattern form a Fabry-Perot interferometer which results from 546.1 nm spectral line of a mercury lamp immersed in a uniform magnetic field. The magnetic field is varied from zero to nearly 1 Tesla.
Initially, the light is viewed along an axis perpendicular to the magnetic field axis. A polarizer is used to show the three lines due to light that is polarized parallel to the field axis and to show the six lines that are polarized perpendicular to the field axis. The pattern may also be viewed along the field axis where the light is circularly polarized.
Finally, the pattern that is polarized perpendicular to the field axis is used to calculate the Bohr magneton. All atomic magnetic moments are integral or half-integral multiples of the Bohr magneton.
PASCO Advantage: In PASCO Capstone software, students can use the video magnifier tool to enlarge the region to see the details of the line splitting. Also, the radius tool needs only three points to define the circle, so even rings that are partially out of view can be measured.