Physics Help Forum Basic question on Photons

 Quantum Physics Quantum Physics Help Forum

 Sep 11th 2009, 07:10 AM #1 Senior Member   Join Date: May 2009 Location: Mumbai,India Posts: 102 Basic question on Photons A question which we had in a test. 1)The power output of a source of light emitting photons of a fixed frequency is increased. How does the number of photons per unit volume in the beam change? 2)What will happen to the number of photons per unit volume if the frequency is increased keeping the power output constant? The first part is pretty easy, the number of photons per unit volume will increase if the power output of the source increases keeping the frequency fixed For the second part, I thought the number of photons per unit volume wouldn't change if the power output was kept constant while the frequency increases. But the energy of an individual photon would increase. But it seems I'm wrong. As the power output is constant, and the energy of the individual photon increases, the number of photons per unit volume should decrease. My stupid question: I don't quite understand the meaning of the italics. I mean how can the power output of the source be kept constant while increasing the energy of the quantum? How is it achieved? __________________ Just another brick in the wall...
 Sep 11th 2009, 09:22 AM #2 Physics Team     Join Date: Jul 2009 Posts: 310 Well all you need to do is increase the frequency of the photons but this also decreases the number of photons being ejected per unit time, requiring the machine to be on for longer to supply the same amount of power. $\displaystyle P = \frac {W}{t}$ __________________ "Dissent is the highest form of patriotism." - Thomas Jefferson. "Give me control of a nation's money and I care not who makes her laws." -Mayer Amschel Rothschild I study Mathematical Physics at the University of Waterloo. -DC

 Tags basic, photons, question

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post bigdaddyJ Advanced Mechanics 1 Mar 20th 2015 12:09 PM PhysicsKidd Waves and Sound 1 Jan 16th 2015 06:27 AM lolly Kinematics and Dynamics 1 Jan 5th 2011 09:46 AM George321 Electricity and Magnetism 1 May 3rd 2010 01:01 AM Raj Light and Optics 0 Oct 26th 2008 10:56 AM