Planck’s Constant Photoelectric Effect Apparatus

Planck’s Constant Photoelectric Effect Apparatus

Planck’s Constant Photoelectric Effect Apparatus

This device demonstrates the quantum mechanical property that energy is a function of frequency, not intensity, and to qualitatively show the photoelectric effect and Planck’s constant. This machine is compact, convenient and easy to use.

How It Works
Light shines from a halogen tungsten lamp, passes through a selection of 5 colored filters of different wavelengths and strikes a dark box with a phototube inside. The color filters are slotted to fit the receiver and are quickly and easily changed. The frequency of light incident on the emitter of the phototube causes photoelectrons to be ejected and pass through a vacuum to a collector. The photocurrent and photo voltage are then measured by a meter.

The experiment shows that for any metal, there is a critical frequency that prevents lower frequency light from releasing electrons, while higher frequency light always does. The emission of electrons occurs shortly after the arrival of the radiation, and the number of electrons is proportional to the intensity of that radiation. Completing this experiment provides strong evidence that the electromagnetic field is quantized and that the field consists of quanta of energy (photons): E= hn where n is the frequency of the radiation and h is Planck’s constant.

This device includes a vacuum phototube as the photosensitive device and a tungsten halogen lamp (12V, 35W) as the light source.

With the unit’s optical bench, the light source can be moved to adjust the distance between light source and phototube.

The length of the scale is 400 mm. A focusing lens is attached to the rear end and a pull tube houses the color filters: 635 nm, 570 nm, 540 nm, 500 nm and 460 nm.

Results are displayed on an easy-to-read four-digit LED display (for current in mA or voltage in V).

Features

• Wave length of color filters: 635 nm, 570 nm, 540 nm, 500 nm και 460 nm.
• Light Source: 12V/35W (halogen tungsten lamp)
• Sensitive Component: Vacuum Phototube
• Dark-current: less than 0.003 μΑ
• Precision of accelerate voltage: less than ±0.2%
• Measuring error: less than ±15% compared to the accepted value h=6,62619×10^34 J.S