Photo Definition and 480 Threads

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...

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...

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...

or made less than weekly?

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...

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...

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...

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...

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...

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...

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?

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...

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...

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.

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...

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...

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...

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...

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...

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...

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

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...

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/ :rolleyes:

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...

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...

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.

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...

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

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...

What causes this effect? What am I seeing?

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...

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

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...

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

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...

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...

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...

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

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...

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...

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...

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.

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?

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...

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...

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...

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...

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...

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...

Homework Statement In converting electrical energy into light energy, a sixty-watt incandescent light bulb operates at about 2.2% efficiency. Assuming that all of the light is green light (wavelength approximately 5500 Å), determine the number of photons per second given off by the bulb and...