Explore BrainMass


A photon is an elementary particle. Photons have zero rest mass which allows long distance interactions. The photon is massless, has no electric charge and is stable. A photon has two possible polarization states. Similarly to other elementary particles, photons are best explained by quantum mechanics and wave-particle duality.

A photon moves at the speed of light and its energy and momentum are related by the equation E = pc, where p is the magnitude of the momentum vector p. The energy and momentum of a photon depends only on its frequency or inversely, its wavelength:

E= ℏw=hv= hc/λ

p= ℏk

Where k is the wave vector, w = 2πv is the angular frequency, and ħ = h/2π is the reduced Planck constant.

Photons have applications in modern day technology. The classic photomultiplier tube exploits the photoelectric effect and photons landing on a metal plate. This principal is used in fire detectors. Other detectors use the ability of photons to ionize gas molecules causing a detectable change in conductivity.

The number of photons that enter the eye

I am doing an experiment to determine minimum number of photons that enter the eye. I need the surface area of the eye but only a portion through 1 radian of the surface. Can you please show me the derivation for that integral to find the surface area of a portion of the eye through 1rad?

Atoms, Energy, and the Periodic Table

Assignment Chapter 7 Concept Explorations 7.23. Light, Energy, and the Hydrogen Atom • a. Which has the greater wavelength, blue light or red light? • b. How do the frequencies of blue light and red light compare? • c. How does the energy of blue light compare with that of red light? • d. Does blue li

Calculating the Number of Photons Produced in an X-Ray

An X-ray with energy 60 keV strikes a gadolinium-based intensifying screen, producing photons at a wavelength of 415 nm. The energy conversion coefficient for the process is 20%. How many photons are produced for each incident X-ray? (Planck's constant = 6.63 x 10^-34 J s, 1eV = 1.602 x 10^-19 J.)

Range of Photon Energies.

Compton scattering of photons causes image blurring since the secondary x-ray photon diverges from the primary beam. You are designing an x-ray detector system and wish to eliminate all photons that have scattered more than 25 degrees in an attempt to improve the resulting image quality. You are using monoenergetic x-ray source

Photon numbers

The entrance exposure during a mammography examination is 100mR. (a) Suppose the photon bean consists of photons each of energy 20 keV. How many photons are incident on a 1 cm^2 surface of breast tissue? (b) Now suppose the energy of each photon is 50 keV. How many photons are incident on a 1 cm^2 surface of tissue?

Number of Photons.

3. A 60Co radiation therapy unit is equipped with a 1000 Ci source. The source to skin distance is 100 cm. Estimate how many photons per second are incident on a 1 mm x 1 mm area of skin of a patient. Neglect air attenuation.

Photon Flux

Suppose that x rays are emitted from a focal spot isotropically. The photon flux is 3.28x10^6 photons mm^-2 sec^1 at a distance of 0.75m from the focal spot. What is the photon flux at a distance of 10cm from the focal spot? Neglect the effects of air attenuation.

Energies in Photons of Elements

The energies, E, for the first few states of an unknown element are shown here in arbitrary units. n 1 2 3 4 ... ? E -11 -5 -2 -1 ... 0 A gaseous sample of this element is bombarded by photons of various energies (in these same units). Match each photon to the result of its absorption (or lack thereof) by an n=1 electron

Energy conversion into photons and heat

Answer the following: a) Mention a process in which the energy being absorbed is converted into photons. How are these photons emitted? Give an application of the process. b) Mention a process in which the energy being absorbed is converted into heat. Give an application of the process.

Two Problems in Modern Physics

1;A cathode plate is heated up to 300±C. What is the de Broglie wavelength of electrons it emits? 2.Show that the laws of energy and momentum conservation forbid the complete absorption of a photon by a free proton.

Representation of many particle states as fock states

Can a single Fock state |n> be written as a product of individual photon states, e.g. |2> = |1>|1>? If not, what experiments might show a difference in behavior between a two-photon state |2> and the product state |1>|1> ?

Wavelength of a Photon Carrying Excess Energy from a Collision

A photon of 156.0689 nm electromagnetic radiation encounters an electron in the n = 2 orbital of a hydrogen atom, and causes it to 'jump' to the n = 3 orbital. What will be the wavelength of a photon which carries away any excess energy from the collision?

Estimating the Wavelength of Visible Light

Please help with the following physics problem. The lowest energy visible light photon is the longest wavelength at the red end of the light spectrum. How many times greater is this energy than that of a typical microwave photon with a wavelength of 10^7 nm?

Statistical Distance vs. Actual Distance

Y Statistical Distance vs. Actual Distance, I am grappling with this concept and need a succinct explanation of the difference between statistical distance vs actual distance with some examples of how to calculate the numerical values for each distance. If you are ok with this project let me know and we can arrange a fee

Longest wavelength of light that can be used to dislodge electrons

When a clean chromium surface is irradiated with 237-nm light, the maximum kinetic energy of an ejected electron is 1.173?0^−19 J. What is the longest wavelength of light that can be used to dislodge electrons from the surface of chromium? Give your answer in nanometers, nm. (1 nm = 1?0−9 m)

Scattering Angle, Wavelenght, and Speed for the Electron

See attached file for further details. 3. A 0.650 MeV photon scatters off a free electron such that the scattering angle of the photon is twice the scattering angle of the electron (Fig. P40.31). (a) Determine the scattering angle for the electron. [ ]° (b) Determine the final speed of the electron. [

wavelength of a photon emitted

Consider an electron in an infinite well of width 0.5 nm. Given : h(bar) = 1.05457 x10^−34 J s , RH = 1.09735 x10^7 m−1 , a0H = 5.29177 x 10−11 m, and E0H = 13.6057 eV . What is the wavelength of a photon emitted when the electron in the infinite well makes transition from the first excited state to the gr

Solid Angle of Cylindrical Detector and Intrinsic Peak Efficiency

Find the solid angle subtended by the circular end surface of a cylindrical detector (diameter of 10 cm) for a point source located 20 cm from the surface along the cylindrical axis. Also, assume that this detector has an intrinsic peak efficiency at 1 MeV of 12%. The point source emits a 1 MeV gamma ray in 80% of its deca

Initial and Final States of Hydrogen

A hydrogen atom in an excited state emits a photon of wavelength 95 nm. Select the initial and final states of the hydrogen atom. 1 2 3 4 5 6 7

A photon of wavelength 2.27 x 10^-8 m

Please explain answers A photon of wavelength 2.27 x 10^-8 m has the minimum energy required to remove the single electron from an ion in its lowest energy state. (a) Identify the ion (b) What is the wavelength of the longest wavelength radiation absorbed by this ion in its lowest energy state? What region of the electrom

Photon Energies and Balmer Series

(See attached file for full problem description) --- Note on problem solving. A handy way to calculate photon energies and wavelengths is as follows: We know E = hc/lambda and  = hc/E for photons. The quantity hc may be expressed as 1240 eV-nm. Thus, a 2.0-eV photon as a wavelength lambda = (1240 eV-nm)/(2.0

Thin-Film Interference

We have not covered in class yet and the book does not offer much help. Is it asking for the value (m)? If so how is that determined? Thanks. Light of wavelength 616 nm (in vacuum) is incident perpendicularly on a soap film (assume n = 1.36) suspended in the air. What are the two smallest nonzero film thicknesses (in nm) f

Photoelectrons Produced by Beams of Light

Two beams of light with different wavelengths (A > B) are used to produce photoelectrons from a given metal surface. (b) Find Kmax for cesium (W0 = 1.9 eV) if A = 570 nm, and B = 330 nm. Kmax, A ___ eV Kmax, B ___ eV.


These are some tips to remember the following easily wavelength of X-rays produced and the dependence of wavelength and energy on the accelerating potential etc.