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Light rays coming out of a flashlight. The photons are depicted as small ellipses enclosing a wave each and moving in the direction of the rays. Energies of photons are labeled as E and E prime, where E is equal to h f and E prime is equal to h f prime.
An EM wave of frequency f size 12{f} {} is composed of photons, or individual quanta of EM radiation. The energy of each photon is E = hf size 12{E = ital "hf"} {} , where h size 12{h} {} is Planck’s constant and f size 12{f} {} is the frequency of the EM radiation. Higher intensity means more photons per unit area. The flashlight emits large numbers of photons of many different frequencies, hence others have energy E = hf size 12{E' = ital "hf"'} {} , and so on.

The photoelectric effect has the properties discussed below. All these properties are consistent with the idea that individual photons of EM radiation are absorbed by individual electrons in a material, with the electron gaining the photon’s energy. Some of these properties are inconsistent with the idea that EM radiation is a simple wave. For simplicity, let us consider what happens with monochromatic EM radiation in which all photons have the same energy hf size 12{ ital "hf"} {} .

  1. If we vary the frequency of the EM radiation falling on a material, we find the following: For a given material, there is a threshold frequency f 0 size 12{f rSub { size 8{0} } } {} for the EM radiation below which no electrons are ejected, regardless of intensity. Individual photons interact with individual electrons. Thus if the photon energy is too small to break an electron away, no electrons will be ejected. If EM radiation was a simple wave, sufficient energy could be obtained by increasing the intensity.
  2. Once EM radiation falls on a material, electrons are ejected without delay . As soon as an individual photon of a sufficiently high frequency is absorbed by an individual electron, the electron is ejected. If the EM radiation were a simple wave, several minutes would be required for sufficient energy to be deposited to the metal surface to eject an electron.
  3. The number of electrons ejected per unit time is proportional to the intensity of the EM radiation and to no other characteristic. High-intensity EM radiation consists of large numbers of photons per unit area, with all photons having the same characteristic energy hf size 12{ ital "hf"} {} .
  4. If we vary the intensity of the EM radiation and measure the energy of ejected electrons, we find the following: The maximum kinetic energy of ejected electrons is independent of the intensity of the EM radiation . Since there are so many electrons in a material, it is extremely unlikely that two photons will interact with the same electron at the same time, thereby increasing the energy given it. Instead (as noted in 3 above), increased intensity results in more electrons of the same energy being ejected. If EM radiation were a simple wave, a higher intensity could give more energy, and higher-energy electrons would be ejected.
  5. The kinetic energy of an ejected electron equals the photon energy minus the binding energy of the electron in the specific material. An individual photon can give all of its energy to an electron. The photon’s energy is partly used to break the electron away from the material. The remainder goes into the ejected electron’s kinetic energy. In equation form, this is given by
    KE e = hf BE , size 12{"KE"= ital "hf" - "BE"} {}
    where KE e size 12{"KE" rSub { size 8{e} } } {} is the maximum kinetic energy of the ejected electron, hf size 12{ ital "hf"} {} is the photon’s energy, and BE is the binding energy    of the electron to the particular material. (BE is sometimes called the work function of the material.) This equation, due to Einstein in 1905, explains the properties of the photoelectric effect quantitatively. An individual photon of EM radiation (it does not come any other way) interacts with an individual electron, supplying enough energy, BE, to break it away, with the remainder going to kinetic energy. The binding energy is BE = hf 0 size 12{"BE "= ital "hf" rSub { size 8{0} } } {} , where f 0 size 12{f rSub { size 8{0} } } {} is the threshold frequency for the particular material. [link] shows a graph of maximum KE e size 12{"KE" rSub { size 8{e} } } {} versus the frequency of incident EM radiation falling on a particular material.

Questions & Answers

a rare fraction and adjacent contraction of a sound wave are travelling in air and are separated by distance of 15cm, taken that velocity sound is 330ms what is the frequency?
Jennifer Reply
u need answer
Abbas
yes pls
Jennifer
Is ans 64/3
yuvraaj
2200hertz
chiadikaobi
what is speed and velocity
Yaseer Reply
speed is scaler quantity and velocity is vector quantity speed has only magnitude and velocity has magnitude+direction both speed and velocity has same unit m/s
shubham
I am finding it hard to draw the velocity time graph, please can anyone assist me to know how to draw it, please?
bona
explain and draw how to measure length when using ruler, micrometer screw gauge and vernnier calliper
gift Reply
Calculate the average velocity in time interval 6sec to 12sec and determine the instantaneous velocity
Lekiisi Reply
v/6
chiadikaobi
the force is not constant in this case of tow car collide for short period of time ..why is the force is not constant?
Abel Reply
hmmm
Fortune
calculate the average velocity in time interval 6sec to 12sec ad determine the instantaneous velocity
Lekiisi
meaning of the term si units
Chali Reply
what what causes electric current
Chali
what what causes electric current
Chali
Charges(electron)
Caleb
Systeme international unitq@1qa@aaq
Caleb
Correct one international system of units.
Caleb
electric dynamo
albert
Electric dynamo is the sources of electric magnetic forces which utilize electromagnetic induction.
albert
A stone is dropped down a well, if it take 5 seconds to reach the water, how dip is the well
Mollamin Reply
125m dip
chiadikaobi
an aircraft at as steady velocity of 70m/so eastwards at a height of 800me drops a package of supplies .a, how long will it take for the package to rich the ground? b, how fast will it be going as it lands?
Ng Reply
what is hypothesis theory law
Tamba
144.57m/s
chiadikaobi
physics is the science of measurement
Jide Reply
What is physics
Victor Reply
what is physics
Obaro
Good question! Physics is the study of the nature world . Does this help?
Yonn
physics is the study of matter in relations to energy.
Enoch
physics is the science of measurements
Jide
physics is a science concern with nature and properties of matter and energy
Ugomma
what is a parallelogram law of motion?
Nancy
describe how you would find the area of an irregular shaped body?
Chali
physics is the study of natural phenomena at their most fundamental level
Yaseer
Definition for physics
Adesola Reply
It deal with matter and relation to energy
Soughie
physics is the Study of matter in relation to energy.
albert
physics is a natural science that study matter its behaviour and relation to energy.
mohammed
physic tells us more about quantities and measurement also
Kelly
life as we know it that can be measured and calculated
Jesus
what is a reference frame
Chukwu Reply
what is anatomy in relation to physics
Mubarak Reply
how does half life exist
Humble Reply
 The amount of time it takes a radioactive isotope to decay into a stable isotope is different for each radioactive isotope, and is characterized by its “half-life”. An isotope's half-life is the amount of time it takes for half the number of atoms of that isotope to decay to another isotope.
Nardine
what is the difference between Mass and weight
Pjustin
mass is constant while weight varies. unit of mass is kg, unit of weight is newton
Faith
how can a coin float in water and what principle governs it
Mercy Reply
in my opinion that work of surface tension but restrictions on coin is that coin do not break surface energy of molecules but some days before scientists prove that's another types of force
Aman
which force hold floating coins together thats my confusion
Aman
Practice Key Terms 4

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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