![physicus apparatus physicus apparatus](https://img.alicdn.com/imgextra/i4/184711909/TB2Wx23cpXXXXcWXXXXXXXXXXXX_!!184711909.jpg)
Notice that on one side of the imaginary “front-on” perpendicular line from the mercury lamp, the spectral lines are brighter than the similar lines from the other side. Swing the \(h/e\) apparatus box around on its arm, and you should see at various positions, yellow green, and several blue spectral lines on its front reflective mask. Turn on the mercury lamp using the switch on the back of the light box. Your apparatus should be set up approximately like the figure above. The relative transmission percentages are 100%, 80%, 60%, 40%, and 20%.
![physicus apparatus physicus apparatus](https://i.pinimg.com/originals/11/e1/15/11e115cfdf0fde05225fb9fa5b2fa7a3.png)
The variable transmission filter consists of computer-generated patterns of dots and lines that vary the intensity of the incident light. Turn the grating around to verify that you have the optimal orientation. A “blazed” grating, which has a preferred orientation for maximal light transmission and is not fully symmetric, is used. The diffraction grating is mounted on the same frame that holds the lens, which simplifies the setup somewhat. A lens focuses the aperture on the photodiode window. The optical components include a fixed slit (called a light aperture) which is mounted over the output hole in the front cover of the light box. To facilitate mounting of the filters, the light box is equipped with rails on the front panel. In order to prevent the possibility of getting an electric shock from the high voltage, do not remove the cover from the unit when it is plugged in. The transformer is fed by a 115-volt power source from an ordinary wall outlet. The equipment consists of a mercury vapor light housed in a sturdy metal box, which also holds the transformer for the high voltage. A color filter at the entrance of the photodiode is used to minimize room light. The desired wavelength is selected with the aid of a collimator, while the intensity can be varied with a set of neutral density filters. For this purpose, we use a high-quality diffraction grating with 6000 lines per centimeter. Mercury light has five narrow spectral lines in the visible region - yellow, green, blue, violet, and ultraviolet - which can be separated spatially by the process of diffraction. The light is formed by an electrical discharge in a thin glass tube containing mercury vapor, and harmful ultraviolet components are filtered out by the glass envelope. This experiment requires the use of several different monochromatic light beams, which can be obtained from the spectral lines that make up the radiation produced by excited mercury atoms. You should replace the batteries if the voltage is less than 6 volts. The battery test points are located on the side panel. To check the batteries, you can use a voltmeter to measure the voltage between the output ground terminal and each battery test terminal. There are two 9-volt batteries already installed in the photodiode housing. However, the anode output does stabilize once the photoelectrons charge it up. The amplifier output will not stay at 0 volts very long after the switch is released. To speed up this process, a shorting switch is provided it is labeled “Push to Zero”. It would take considerable time to discharge the anode at the completion of a measurement by the usual high-leakage resistance of the circuit components, as the input impedance of the amplifier is very high. The amplifier enables us to investigate the minuscule number of photoelectrons that are produced.
![physicus apparatus physicus apparatus](https://i.stack.imgur.com/0CH4T.jpg)
To measure the stopping potential, we use a very sensitive amplifier which has an input impedance larger than 10 13 ohms. When the voltage across this “capacitor” reaches the stopping potential of the cathode, the voltage difference between the cathode and anode (which is equal to the stopping potential) stabilizes. The photodiode and its associated electronics have a small “capacitance” and develop a voltage as they become charged by the emitted electrons. To prevent the collision of electrons with air molecules, the diode tube is evacuated. The diode has a window which allows light to enter, and the cathode is a clean metal surface. The central element of the apparatus is the photodiode tube. In this experiment, we will measure the stopping potential with modern electronics. If the value of the electron charge \(e\) is known, then this equation provides a good method for determining Planck's constant \(h\). \begin\) and the light frequency \(f\), with slope \(h/e\) and vertical intercept \(-W_0/e\). The energy quantization of electromagnetic radiation in general, and of light in particular, is expressed in the famous relation Source of monochromatic light beams to irradiate photocathode.Digital voltmeter to read reverse voltage.Batteries to operate amplifier and provide reverse voltage.