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# Inquiry: Photoelectic Effect

## Procedure:

Using the above applet choose one of the known metal targets and make a graph in Excel of Kinetic Energy of ejected photoelectrons versus frequency of incoming photons. Try to get about 8-10 data points for each graph by decreasing your wavelength and recording the electron-volts needed to force the electrons backwards so that there is no current. Record your voltage and your wavelength. You must convert electron-volts to Joules. (1.0 eV = 1.6x-19 J) You also need to convert wavelength (nm) into frequency (Hz). Determine Planck's constant, work function and the frequency cutoff and wavelength cutoff in nm for that particular metal. Enter your graph and all calculations into your notebook.

Einstein's photoelectric equation is as follows:

## Inquiry Questions:

1. Describe how the number of photoelectrons emitted from the metal surface varies with light intensity--that is, how does the output current of the ammeter vary with the brightness of the light?

2. Describe how the kinetic energy of the photoelectrons depends on intensity--that is, how does the stopping voltage change if you make the light brighter?

3. Describe how the stopping voltage and hence the KE of the photoelectrons varies as the light is changed from red through blue?

4. 400.0 nm blue light hits potassium metal with a work function of 2.0 eV. With what velocity will an electron be emitted from the potassium metal?