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Desexcitation X-rays : Finally, what happens to the atom left in an excited state? It inherits a surplus of energy equal to the binding energy of the expelled electron. The atom will reorganize itself and return this surplus. If the gamma has removed a K-shell electron, an electron belonging to the higher L shell will fill the vacancy left on the K-shell.
During the transition a characteristic X-ray is emitted. This emission of desexcitation X-rays is sometimes called X fluorescence. When the X-ray is emited in dense matter it is usually absorbed after a short range. EN FR. Photoelectric Effect The most effective mechanism of photon absorption Gamma absorption by an atom The photoelectric effect occurs in two stages.
First, the photon a takes out a bound electron in one atom. Hz; 0. The wavelengths of visible light range from approximately to nm. What is the corresponding range of photon energies for visible light? What is the longest wavelength of radiation that can eject a photoelectron from silver? Is it in the visible range?
What is the longest wavelength of radiation that can eject a photoelectron from potassium, given the work function of potassium 2. Estimate the binding energy of electrons in magnesium, given that the wavelength of nm is the longest wavelength that a photon may have to eject a photoelectron from magnesium photoelectrode.
The work function for potassium is 2. What is the cutoff frequency when this metal is used as photoelectrode? What is the stopping potential when for the emitted electrons when this photoelectrode is exposed to radiation of frequency THz? Estimate the work function of aluminum, given that the wavelength of nm is the longest wavelength that a photon may have to eject a photoelectron from aluminum photoelectrode.
What is the maximum kinetic energy of photoelectrons ejected from sodium by the incident radiation of wavelength nm? A nm UV radiation illuminates a gold-plated electrode. What is the maximum kinetic energy of the ejected photoelectrons? A nm violet light ejects photoelectrons with a maximum kinetic energy of 0. What is the work function of sodium? A nm light falls on a photoelectric surface and electrons with the maximum kinetic energy of 0.
Determine a the work function and b the cutoff frequency of the surface. The cutoff wavelength for the emission of photoelectrons from a particular surface is nm. Find the maximum kinetic energy of the ejected photoelectrons when the surface is illuminated with light of wavelength nm.
Find the wavelength of radiation that can eject 2. The work function for calcium is 2. In what range is this radiation? Find the wavelength of radiation that can eject 0. Find the maximum velocity of photoelectrons ejected by an nm radiation, if the work function of photoelectrode is 4. Skip to content Photons and Matter Waves. An experimental setup to study the photoelectric effect.
The anode and cathode are enclosed in an evacuated glass tube. The voltmeter measures the electric potential difference between the electrodes, and the ammeter measures the photocurrent.
The incident radiation is monochromatic. The absence of lag time When radiation strikes the target material in the electrode, electrons are emitted almost instantaneously, even at very low intensities of incident radiation. The intensity of incident radiation and the kinetic energy of photoelectrons Typical experimental curves are shown in Figure , in which the photocurrent is plotted versus the applied potential difference between the electrodes.
The detected photocurrent plotted versus the applied potential difference shows that for any intensity of incident radiation, whether the intensity is high upper curve or low lower curve , the value of the stopping potential is always the same. Kinetic energy of photoelectrons at the surface versus the frequency of incident radiation. The photoelectric effect can only occur above the cut-off frequency Measurements for all metal surfaces give linear plots with one slope.
Each metal surface has its own cut-off frequency. Photocurrent drops to zero at the stopping value of potential, so we identify Solution We use Figure to find the kinetic energy of the photoelectrons:.
Summary The photoelectric effect occurs when photoelectrons are ejected from a metal surface in response to monochromatic radiation incident on the surface. It has three characteristics: 1 it is instantaneous, 2 it occurs only when the radiation is above a cut-off frequency, and 3 kinetic energies of photoelectrons at the surface do not depend of the intensity of radiation.
The photoelectric effect cannot be explained by classical theory. We can explain the photoelectric effect by assuming that radiation consists of photons particles of light. Each photon carries a quantum of energy. Figure 1. The photoelectric effect can be observed by allowing light to fall on the metal plate in this evacuated tube. Electrons ejected by the light are collected on the collector wire and measured as a current.
A retarding voltage between the collector wire and plate can then be adjusted so as to determine the energy of the ejected electrons. For example, if it is sufficiently negative, no electrons will reach the wire.
This effect has been known for more than a century and can be studied using a device such as that shown in Figure 1. This figure shows an evacuated tube with a metal plate and a collector wire that are connected by a variable voltage source, with the collector more negative than the plate. When light or other EM radiation strikes the plate in the evacuated tube, it may eject electrons.
If the electrons have energy in electron volts eV greater than the potential difference between the plate and the wire in volts, some electrons will be collected on the wire. Since the electron energy in eV is eV , where q is the electron charge and V is the potential difference, the electron energy can be measured by adjusting the retarding voltage between the wire and the plate.
The voltage that stops the electrons from reaching the wire equals the energy in eV. For example, if —3. The number of electrons ejected can be determined by measuring the current between the wire and plate. The more light, the more electrons; a little circuitry allows this device to be used as a light meter. What is really important about the photoelectric effect is what Albert Einstein deduced from it.
Einstein realized that there were several characteristics of the photoelectric effect that could be explained only if EM radiation is itself quantized : the apparently continuous stream of energy in an EM wave is actually composed of energy quanta called photons.
In his explanation of the photoelectric effect, Einstein defined a quantized unit or quantum of EM energy, which we now call a photon , with an energy proportional to the frequency of EM radiation. It is the quantization of EM radiation itself. EM waves are composed of photons and are not continuous smooth waves as described in previous chapters on optics.
Their energy is absorbed and emitted in lumps, not continuously. We do not observe this with our eyes, because there are so many photons in common light sources that individual photons go unnoticed. See Figure 2. The next section of the text Photon Energies and the Electromagnetic Spectrum is devoted to a discussion of photons and some of their characteristics and implications. For now, we will use the photon concept to explain the photoelectric effect, much as Einstein did.
Figure 2. An EM wave of frequency f is composed of photons, or individual quanta of EM radiation. What scientific concept do you need to know in order to solve this problem? Our tutors have indicated that to solve this problem you will need to apply the Bohr Equation concept. You can view video lessons to learn Bohr Equation.
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