What is Photo: Definition and 505 Discussions

A photograph (also known as a photo) is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are created using a smartphone/camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of what the human eye would see. The process and practice of creating such images is called photography.

View More On Wikipedia.org
Recent contents Top users
  1. 1rel

    Learning Photo Flasher Circuit Basics

    Hello everyone I'm new here, and currently trying to learn more about electronics. - Since my knowledge is very limited, I've decided to take apart some old devices from the garbage, and recently tried to understand a photo flash circuit from an old camera, and to trigger it with my own bench...
  2. ZapperZ

    VOTE Photo Contest - It's Good To Be Back

    A lot of photos submitted to the contest this week, even though some of them are a bit vague in how they connect to the topic. Still, I'll give them the benefit of a doubt this time around (it will become more strict after this). As always, please vote for the photo that best reflects our...
  3. ZapperZ

    Pf photo contest - it's good to be back (9/20-9/26)

    It's Good To Be Back! The more things change, the more things stay the same! With the new PF look and new engine, it looks like the Mentors are also bringing back the same old thing - ME! I'm partially coming out of my retirement to continue running the PF Photo Contest in the next foreseeable...
  4. epenguin

    Is the photo competition being abandoned?

    or made less than weekly?
  5. L

    Direction of Photo Electron Emission

    I was looking for information on how the photo electrons are emitted when under X-ray radiation. In this ancient review paper here http://journals.aps.org/pr/pdf/10.1103/PhysRev.30.488 they state that the most common angles for non polarized X-ray beams (of various energies) range roughly at...
  6. A

    How Does Shot Noise in a Photodiode Lead to White Noise Characteristics?

    Not really sure where this belongs... But here goes: If you illuminate a photo diode it generates a current because electrons are being emitted from its cathode. Since each emission is however an independent stochastic process the output current will be subject to fluctuations, which can be...
  7. N

    Finding initial wavelength of photo given angle of deflection

    Homework Statement Find the initial wavelength of a photon that loses half its energy when it Compton-scatters from an electron and emerges at 90∘ to its initial direction of motion. The Attempt at a Solution Ei = Ef +KE Ei = 0.5Ei + KE Using compton's formula for scattering...
  8. N

    Compton effect photo scatterred

    Homework Statement A photon of wavelength 29 pm is scattered by a stationary electron. What is the maximum possible energy loss of the photon? (mass of electron = 9.11 × 10-31 kg, h = 6.626 × 10^-34 J · s, c = 3.00 × 10^8 m/s) The Attempt at a Solution After an hour or so, I'm...
  9. L

    Is this photo physically possible?

    I am looking for expert commentary on this photo. I am hypothesizing that the shadow on the far-left figure is impossible. My reasons are: 1. The sun is 93 million miles away and must cast shadows of parallel angles. 2. The appearance of shadows are a physical phenomena and not dependent on...
  10. mesa

    Fe Ag reactions in used photo fix solution question.

    I had two griffin beakers with 200mL of used photo fix solution on magnetic stirrers ready for electrolysis only to find the power supply was not up to snuff. The backup plan was a redox reaction of Fe with Ag in solution and figure the difference of weight from the set of griffon beakers...
  11. F

    MHB How many ways can equal number of men and women line up for a photo?

    In how many ways can a non-empty collection of people to be chosen from 4 men and 3 women to lineup for a photo if the number of men must be the same as the number of women? I said {4 \choose 1} {3 \choose 1} 2! +{4 \choose 2} {3 \choose 2} 4! + {4 \choose 3} {3 \choose 3} 6! Is this right?
  12. C

    Exploring Photo Fission: Understanding Its Limitations and Possibilities

    I was talking to a person that studies photo fission and i asked if I could shoot a couple of lower energy photons to cause fission. But he said it wouldn't work I would need 1 high energy one. I am not completely sure why this wouldn't work. Does the photon have to get absorbed at one point...
  13. A

    Finding the Optimal Aperture Stop for a Portrait Photo

    Homework Statement A photographer is taking a portrait photo of a person at 6 m distance from his digital camera, which has a sensor pixel size of 10 μm and is equipped with a f = 100 mm thin lens. Image blur is supposed to be limited to the size of one pixel. Which of the following...
  14. M

    Extent of human radio broadcasts photo

    Let me remind you all how small we are :D not that most of you need to be told :P Credit for the photo belongs to Nick Risinger. Website credits in the bottom left hand side of the picture.
  15. T

    Voltage comparator in a photo sensing circuit

    Hello, I attached a picture below but I am confused as to how the voltage comparator is comparing the two inputs (I know how a comparator works). The test points are running down to the two inputs but wouldn't the voltage always be identical across them since voltage doesn't drop in a parallel...
  16. J

    Photo of Enrico Fermi includes math/physics I do not understand

    The attached jpeg shows Enrico Fermi at the blackboard. There is a geometric drawing and some math I do not understand. Can you point me in the right direction? I have searched for a discussion of what he is presenting but cannot find one. The photo may be familiar because it was...
  17. A

    Is the equation(s) in this photo legitimate?

    I am an undergraduate student beginning my journey to be a physicist. On that basis, things like this intrigue me even though I can't read it. Is the equation(s) in this photo legitimate? If so, what do they mean? If you are unfamiliar with this man, he is currently in prison for barraging a...
  18. Gliese123

    Photo of Jupiter's moons with cellphone

    Hi there! Well, it's not just a photo taken by a cellphone but a cellphone plus a very good binocular. And as surprised as I became by being able to see the moons of Jupiter, I took a photo of them through, yes through the binocular. The result is what you see on the picture. And I wanted to...
  19. T

    Photo electric effect review liboff ch2

    Homework Statement Here's the question: A monochromatic point source of light radiates 25 W at a wavelength of 5000 angstroms. A plate of metal is placed 100 cm from the source. Atoms in the metal have a radius of 1 angstrom. Assume that the atom can continually absorb light. The work...
  20. K

    Exploring the Density of Star Trails in National Geographic Photo

    National Geographic is featuring this star trail picture this week on their wallpaper page (found here http://ngm.nationalgeographic.com/your-shot/weekly-wrapper/2012/img/0812wallpaper-week-4-1_1600.jpg). In the picture though I was wondering why the star trails appear so much more dense on the...
  21. D

    Photo Current to voltage conversion

    Why do we require a current to voltage coverter at the output of a photo detector circuits?
  22. A

    Need help with a photo booth I'm working on for a party

    Hi all, I'm helpnig my wife put together a party for our son. She wanted to do a photobooth idea and tasked me with doing it. I need help with the set up though: I'd like to have people go into the photobooth and trigger the camera (either digital camera or USB) and flash using a wired...
  23. S

    Nuclear Photo Reaction + Threshold Energy

    Homework Statement I am given a scenario where a photon and a nuclei interact and create two daughter nuclei/particles. I won't bother with the full scenario as it would be nice to solve this generally, but we may assume we know the mass of all nuclei involved. The question is then what...
  24. MacLaddy

    Chemistry Department Photo: What's Happening in the Picture?

    Ignoring the school, links, and overall blandness of this website; can somebody PLEASE explain to me what is happening in the picture to the left? http://www.slcc-science.org/chem/ :uhh:
  25. H

    Measuring distance between objects of known size in photo

    Hi. I'm wondering if it's an acceptable method of measuring distance between two objects of known size by averaging their scales. In my case I have a photo of birds on the water. Each bird is known to be about 37cm long. I want to find the distance between two of them on the photo, the nearest...
  26. J

    Explaining a Physics Phenomenon with a Snowy Photo

    Homework Statement I have to submit a photo for a physics contest. I was thinking of using the picture in the attached, but I'm having trouble trying to figure out how to explain it in terms of physics. The background on the picture is: We had a very wet snow and as the snow built up on top...
  27. S

    Is this ghost photo real or just a misleading illusion?

    http://img7.imageshack.us/img7/5265/ghostgirlq.jpg my friends were still in shock seeing the ghost between them in the photo, can anyone debunk it.. load it at photoshop and see how it gets there. Others in the building claim to see the ghost girl at times with their own eyes.
  28. L

    Convert DC to AC for Photo Voltaic Systems

    Hi there I have an Photo Voltaic system size 141 kW DC. It gives me an about 13 000 kW/hr a month.(I'm in Hawaii) We planning to install a new system, size ≈800 kW DC. How can i calculate how much of kW/hr AC i will get out of new system? Is there is any special formula to covert DC to AC...
  29. Andre

    Too Much of a Good Thing: Photo Contest Dilemma

    That's the subject of a photo contest somewhere. So I played with matches but "embarras de richesses"; which one to enter? Which one appeals the most? #1 #2 #3 #4 #5
  30. L

    Negative Work function in Photo electric effect

    Homework Statement In my attachment, the x intercept gives threshold frequency and the y intercept gives the work function. Homework Equations The Attempt at a Solution Work function is the minimum energy needed to pull out an electron from the metal surface. My question is, from...
  31. J

    Distorted grid effect in photo of LCD screen

    What causes this effect? What am I seeing?
  32. M

    Photo Reactive Dye: Irreversible Change in Presence of Light

    Homework Statement im trying to identify photo reactive dye/ compound that changes color when exposed to light, i know of photochromic dyes, unfortunately photochromic dyes undergo a reversible change in appearance. is there a compound that changes in the presenc eof light irreversibly...
  33. M

    Photoelectric Effect: Insufficient Energy Collision

    what happens if a photon with insufficient energy to overcome the work function collide with a electron.
  34. W

    Can adding context snippets to photo contest entries improve voting decisions?

    When members post photos for the contests, they sometimes have a small snippet/phrase which helps put their photo in context. I feel when a new voting thread is opened, these snippets might be placed along with the photo, if we voters don't remember what the picture was about when we saw the...
  35. M

    News Watchdog seeks bin Laden photo, says White House 'not above the law'

    http://news.blogs.cnn.com/2011/06/10/watchdog-seeks-bin-laden-photo-says-white-house-not-above-the-law/?hpt=hp_t2 Thoughts?
  36. J

    Classifying light by photo statistics - poissonian, sub, super poissonian?

    I've got three types of light: - star light - light from a discharge lamp - light from a laser emitted high above threshold and I need to decide on which type of counting statistics are expected for the detection of each source: poissonian, super poissonian or sub-poissonian. However, I'm unsure...
  37. P

    What is the Photoelectric Effect?

    Homework Statement When light of wavelength 298 nm is incident on potassium, the emitted electrons have maximum kinetic energy of 1.65 eV. A)What is the energy of an incident photon? The value of h c is 1240 eV · nm . Answer in units of eV. B)What is the work function for potassium? Answer in...
  38. A

    Photoelectric Effect: Green vs Indigo Light

    Homework Statement A surface ejects electrons when hit by green light but not when hit by yellow light. Will the number of photoelectrons ejected be changed if the surface is hit by indigo light? A) yes B) No C) yes, if the indigo light is quite intense Homework Equations E = hv...
  39. A

    Photoelectric Effect: Max Speed Dependency & Graphical Representation

    In what manner is max speed of photo electron dependent on the incident ray? Could i see a graphical representation of it? I thought it would be directly proportional but it isn't so. Thank you
  40. DaveC426913

    Researching a digital photo frame

    I have a digital photo frame that's pooped out on me. In attempting to replace it, I am really disappointed with the digital photo frames I've looked at at Best Buy. Half of them did not work and the other half were so unintuitive that I could not figure out how to operate them without the...
  41. F

    Photo showing decimated reactor building troubles me

    Look at this photo of the severe damage to one of the fukashima reactor buildings (I'm not sure which one) and tell me that the containment structure and/or reactor vessel have not been severely damaged? Judging from the photo, 3/4 of the reactor building has been obliterated. Nobody is saying...
  42. B

    Photo electric effect problem.

    In a photoelectric-effect experiment, the stopping potential at a wavelength of 400 nm is 25.7% of the stopping potential at a wavelength of 300 nm. Of what metal is the cathode made? So I need to find the stopping potential of the metal with a wave length of 400 nm, but first I need to...
  43. Dembadon

    News Married Congressman Resigns After Scandalous Photo

    I bet http://www.guardian.co.uk/world/2011/feb/10/congressman-resigns-after-topless-picture-published" does! Shame on him for posing as a single person when, in fact, he's married. I hope his career is ruined.
  44. KevinMWHM

    Calculating Distance from Model Rocket Photo

    Launched a model rocket with my 5 & 3 year old, have a photo of the rocket straight overhead at the approx peak. Can I figure out the distance? I know the length, and the magnification. What would the formula be?
  45. ZapperZ

    Photo Contest: Join the Fun on Nov 13!

    Hello Everyone! We are reviving the PF Photo Contest! Thanks to Andre for hosting it the past year. The PF Photo Contest will continue with its usual rules, and will continue in its current forum, which is the https://www.physicsforums.com/forumdisplay.php?f=198" forum. However, to make...
  46. B

    Photo electri question longest wave length

    Homework Statement In a photoelectricc experiment,electrons are emitted from a surface illuminated by light of wavelength of 4000*(10^-10), and the stopping potential for these electron is found to be 0.5V. what is the longest wavelength of light that can illuminate this surface and still...
  47. L

    Understanding Photodivision and Electrodivision in Electron Beam Oncology

    Im reading a paper about use of electron beams in oncology and it says: "The mechanism of neutron production in the region of electron beam energies under consideration is determined by photodivision of nuclei by bremsstrahlung photons and the small contribution of electrodivision by...
  48. Ivan Seeking

    Investigating the Alleged Ghost Photo

    I was sent this photo of an alleged ghost. The story is that this is the first photo taken with a new cell phone. Is this some kind of inside joke or something? I don't suppose someone with the cell phone company is having a little fun? Could it be an error of some kind that allowed a...
  49. Z

    Analysing Op Amp Circuit with a Photo diode

    For a lab we built the following circuit. Our photo diode was receiving a blinking signal which our op amp made visible on a DVM. I do not understand the purpose of the capacitors attached to the power rail. So far I understand how negative feed back with the Rf resistor controls the amount...
  50. T

    Can anybody find a mistake in this Avatar photo?

    My professor showed us this photo from Avatar and asked if anybody could find a mistake within it, but I can't see it! Can you tell what is wrong with it? http://img291.imageshack.us/img291/6331/pandoraavatar.jpg The mass closest to us is Pandora and there is a small thing off to the right...
Back
Top