Photoelectric Effect -02- Kinetic Energy

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The threshold wavelength of photoelectricity in a metal is 2000 Å. The kinetic energy of photoelectrons when the metal surface is exposed to a wavelength of 1400 Å in electron volts is...   Watch videos related to MODERN PHYSICS:  https://dailymotion.com/playlist/x90qrm   #Photoelectric

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00:00Hey guys, stop complaining and start learning to achieve your dreams.

00:07We know that every metal has a specific work function.

00:13When the surface receives energy exceeding the work function, what happens to the photoelectrons?

00:21In this problem, we look at two wavelengths.

00:25The threshold wavelength and the test wavelength.

00:28In addition, there is Planck's constant and the speed of light in a vacuum.

00:35We will use these quantities to determine the kinetic energy of the photoelectrons.

00:42Let's discuss them.

00:44Before we go any further, first write down some of the physical quantities shown on the problem sheet.

00:52Just to refresh your understanding, this is a metal surface.

00:58On that surface, there are several free electrons.

01:04When these electrons receive energy at the threshold wavelength, they will appear on the metal surface, not moving anywhere.

01:11A stationary object has kinetic energy of zero.

01:18That's why this wavelength is known as the threshold wavelength.

01:21However, when the wavelength is shorter than the threshold wavelength, the photoelectrons still have excess energy.

01:31This energy manifests as kinetic energy.

01:39This energy causes the photoelectrons to move at a constant speed away from the metal surface.

01:47Mathematically, kinetic energy is equal to Hc over lambda, minus Hc over lambda Th.

01:53The units of energy in this equation are jowls.

02:01Since the units of wavelength are angstroms, it's helpful to use electron volts.

02:11This equation can be written as follows.

02:13Lambda and lambda Th are already written on the problem sheet.

02:22If the numbers look like this, we can use a scientific calculator.

02:27The kinetic energy is approximately 2.66 electron volts.

02:32This is the kinetic energy of the electron.

02:36Happy learning, everyone!

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