What is Per: Definition and 565 Discussions

PeR (Please Explain the Rhythm) is a Latvian pop and beatboxing band formed in 2007. The original line-up was Ralfs Eilands, Emīls Vegners, and Pēteris Upenieks. Vegners left the band in 2007 and was replaced by Edmunds Rasmanis. But when Upelnieks left the trio in 2011, he was not replaced, rendering the band a duo consisting of just Eilands and Rasmanis. After three failed attempts in earlier years to represent Latvia in the Eurovision Song Contest, PeR won the 2013 Dziesma contest and represented the country in the 2013 Contest with the song "Here We Go" and placed last in the second semi-final.

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  1. I

    How to calculate angular momentum per second for a photon?

    Homework Statement Given a photon polarization state lphi> = lx> 3/5 + ly> 4i/5 , a beam of photons transmit N photons per second in such a state. An L-polarized photon has an angular momentum hbar along its direction of motion, and an R-polarized photon has an angular momentum of the same...
  2. S

    Work Done per Unit Charge vs Current

    A trivial question. I know that current is the amount of charge passing per unit time across a area. And Potential difference is change in potential or change in potential energy per unit charge or work done per unit charge. And also from Ohms law, V is directly proportional to I. So...
  3. karush

    MHB Angle $\theta$ Changing Rate of Ladder $13ft$ Long

    A Ladder $13ft$ long is leaning against the side of a building. If the foot of the ladder is pulled away from the building at a constant rate of $\displaystyle \frac{2 in}{sec}$ how fast is the angle formed by the ladder and the ground changing in $\displaystyle\frac {rad}{sec}$ at the instant...
  4. karush

    MHB How Fast Do Carousel Rides Travel in Miles per Hour?

    the rides on a carousel are represented by $2$ circles with the same center with $\displaystyle\omega=\frac{2.4 \text {rev}}{\text {min}}$ and the radius are: $r_{13}=13 \text{ ft} 11 \text { in}= 167 \text { in}$ $r_{19}=19 \text{ ft} 3 \text { in}= 231 \text { in}$ find...
  5. skate_nerd

    Wavelength for highest radiation per unit wavelength

    Homework Statement At what wavelength does a cavity at 6000 degrees Kelvin radiate most per unit wavelength? Homework Equations $$\rho_T(\lambda)d\lambda=\frac{8\pi{hc}}{\lambda^5}\frac{d\lambda}{e^{{hc}/{\lambda{kT}}}-1}$$ The Attempt at a Solution I'm pretty new to this whole...
  6. N

    Exploring the World with a Different Speed of Light: A Hypothetical Scenario

    I'm thinking about speed the speed of light. It is really interesting constant. What would the world (if it ever was), if this value was different? :-) In the microworld, macroworld, in the life of humans, animals and plants ... Ok, I say the c = 1000 kilometer per hour = 278 meters per second...
  7. N

    Calculate the cost of the energy lost to heat per hour per meter

    Homework Statement A small city requires about ##17 \mbox{MW}## of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at ##120 V##. Assuming a two-wire line of 0.60cm -diameter copper wire, estimate the cost of the energy lost to heat per hour...
  8. R

    Series Resistance per unit length of an infinite tranmission line?

    Homework Statement We are to assume an infinite transmission line with the following parameters: capacitance: 296 ρF/ft Zc=52Ω inductance: 8.0 × 10-7 H/ft We are told that a 100MHz signal is attenuated 31 dB per 100 feet and asked based on the information, assuming no leakage through...
  9. T

    Help In understanding Rate Of Change in mm per sec

    Hi everyone Firstly this is not a homework question, i work in transport engineering. ( i do study part time which is why i sometimes post in the homework section) Now to the problem. I am trying to understand how to solve this problem, i already know the answer. A train is traveling...
  10. B

    Charge Volume Density To Charge Per Unit Length

    Homework Statement http://imgur.com/VzZjSEH I took a screen shot so I did not leave anything out. Homework Equations Surface area, and volume of a sphere. The Attempt at a Solution I am trying to find the linear charge density from the charge volume density. I got it explained...
  11. R

    Finding number of atoms per cm^3 of zinc?

    Homework Statement Zinc has a density of 7.17 Mg/m^3. Calculate (a) the number of Zn atoms per cm^3, (b) the mass of a single Zn atom and (c) the atomic volume of Zn. Homework Equations atomic mass of zinc = 65.39 g/mol The Attempt at a Solution For part (a) I use the fact that...
  12. S

    Schools How much did you study per week in university?

    I'm thinking about enrolling into an engineering program soon, I was wondering how many hours per week do you think the average student in mechanical engineering spends studying in class and out of class? Thanks.
  13. A

    How do you find out energy required per day?

    Human body needs about 2000-2500 calories per day. How do you find out this number? What sort of experiments do people do to figure out this number? Also, in general how do you find things like - energy spent while walking, talking, blinking? It almost seems impossible to find out these...
  14. A

    In RBW there are no probabilities per se.

    continuing from another thread. or rewriting physics ? and epistemology and ontology :rolleyes: another acausal model. "The causaloid framework" http://arxiv.org/abs/gr-qc/0509120v1 "Quantum theory is a probabilistic theory with fixed causal structure. General relativity is a deterministic...
  15. PsychonautQQ

    Potential energy per unit length in a string (sin wave)

    Homework Statement Given that the stretched length of a string is Δx(1+1/2(dy/dx)^2) show that the potential energy per unit length is equal to 1/2F(dy(x,t)/dx)^2 Homework Equations potential energy = kx^2 cos(kx-wt) idk really... The Attempt at a Solution The fact that the...
  16. A

    Momentum per unit area per unit time in EM

    Homework Statement In fact it is problem 8.5 in Griffiths 3rd ed p357 Consider an infinite parallel plate capacitor with the lower plate carrying the charger density - \sigma , and the upper plate carrying the charge density + \sigma . (a) Determine all nine elements of the stress...
  17. QuantumCurt

    How many upper level math/physics courses per semester are typical?

    Hey everyone, I've been wondering about this lately. I'm double majoring in physics and math, and I'm looking ahead to the upper level major courses that I'm going to need. How many upper level math/physics courses would be typical/manageable within one semester/quarter? Looking ahead, it...
  18. S

    How many hard science courses can you handle per semester?

    Our math program requires only three math courses per semester so I can elect to take less intesive courses like music or french but our physics program requires four to five physics and math courses per semester. Because of this, I thought of taking three courses per semester and stay a bit...
  19. P

    Magnetic force per unit charge and work done on a proton

    Homework Statement a proton moves with a velocity <6*105,3*105> m/s through a magnetic field given by <.2,.2> T a. Find the magnetic force per unit charge on the proton b. Find the work done by this forceHomework Equations Fm=qv x BThe Attempt at a Solution For part a, I used a property of...
  20. S

    Taking three courses per term in undergrad

    I am a slow learner and I prefer to spend lots of time on few subjects rather than to distribute time over many. In addition, most of my courses will be extremely time consuming. So I probably want to take three courses per term and I will most likely attain a much higher GPA in this way, but I...
  21. C

    MHB Cost per Pound of Coffee Beans

    A coffee house blended 12 pounds of espresso flavored coffee beans with 11 pounds of vanilla flavored coffee beans. The 23 pound mixture cost \$166.50. A second mixture included 17 pounds of espresso flavored coffee beans and 18 pounds of vanilla flavored coffee beans. The 35 pound mixture cost...
  22. J

    Calculating the force required to generate 100 kilowatt per hour

    Hello to everyone, I am trying to calculate how much physical force is needed at point B (imagine a person pushing on a bar attached to point A) to generate 100 kw per hour where the radius is 50 meter. If you imagine that at point A there is a system of gears attached to an...
  23. P

    Equivalent impedance per phase (3 Phase balanced systems)

    Hi, if a load is given in MVA and I work out the Real and reactive power, is the equivalent complex impedance per phase the values of real and reactive power divided by three in the following form: Z (per phase) = Real power/3 + j Reactive power/3 Im not sure how to work out whether the...
  24. M

    Contributions Per Atom in MO diagram

    Homework Statement How do you find the contributions per atom for calculating the reducible parts? For example CO3-2 has pt. grp: D3h. From the character tables-- the first row (unshifted atoms) is: 3,0,1,3,0,1. Second row (coefficients): 1,2,3,1,2,3 Third Row (contributions per atom)...
  25. R

    Find Photons per second on the eye from a source a distance away

    Homework Statement A typical incandescent light bulb emits ~3x10^18 visible-light photons per second. Your eye, when it is fully dark adapted, can barely see the light from an incandescent light bulb 10 km away. How many photons per second are incident at the image point on your retina...
  26. T

    Mr. Fin uses a 710 W hairdryer for 14 minutes per day every day to dry

    Mr. Fin uses a 710 W hairdryer for 14 minutes per day every day to dry his thick, long locks. If the power company charges $0.11/kWh, how much does it cost per month (30 days) to operate the hairdryer? Homework Equations I=q/t The Attempt at a Solution
  27. T

    Photons per Unit Volume (Quantum)

    Homework Statement \rho(\lambda)d\lambda=\frac{8(\pi)hc}{\lambda^{5}}\frac{d\lambda}{e^{hc/(\lambda)KT}-1} What does this represent? Calculate the number of photons per unit volume in a blackbody from \lambda to d\lambda Homework Equations N/A The Attempt at a Solution I...
  28. N

    Define curl rotation per area

    define curl "rotation per area" When they define curl, they say it is a measure of "infinitesimal rotation", or "rotation per area". What does that mean? Does it mean they measure how much something goes around in an infinitesimal point (which makes no sense), kind of like a whirlwind shrunk...
  29. A

    Mass of disk given mass per unit

    Homework Statement I need to find the mass of a disk with a hole, given inner and outer diameters of 0.10m and 0.30m, respectively. The disk has a mass per unit of 20 \frac{kg}{m^2}. The Attempt at a Solution Since I needed mass units, I thought that I could multiply the mass per unit...
  30. marcus

    The awkward expression 1 km/s per Mpc-the radius is better

    The awkward expression 1 km/s per Mpc--the radius is better It's been pointed out that by historical accident we've been stuck with an awkward mix of units conventionally used to express Hubble parameter. If you parse the quantities km/s per Mpc you find that the length units cancel and you...
  31. E

    Fractional energy loss per cycle in a heavy damped oscillator

    http://www1.gantep.edu.tr/~physics/media/kunena/attachments/382/chapter2.pdf On page 9 and 10 of the above PDF the method for deriving the fractional energy loss per cycle in a lightly damped oscillator is described. I understand and follow this derivation. What would the derivation...
  32. A

    Average Binding energy per Nucleon

    What is the Average/mean binding energy per nucleon of the whole periodic table/of all the elements, considering the most naturally abundant isotopes of each element? I tried googling it a couple of times but i could not arrive at a satisfactory answer.
  33. H

    How much energy per unit mass is needed

    Homework Statement How much energy per unit mass (E/m) must you give a rocket to put it into a geosynchronous orbit three Earth radii above the surface of the Earth? Radius of Earth : 6380 km GM/r = 6.25 x 10^7 m^2/ s^2 Homework Equations U(r) = - GMm/r The Attempt at a...
  34. K

    How to Convert Rotations per/sec to radians per second

    Homework Statement How do you convert Rotations per/sec to radians/sec Ex: a disk rotates 15 times in 25 seconds convert to radians/sec Attempt: 15 rotations / 25 seconds = 1 rotation / 0.6 seconds 1 rotations = 2 pi rad
  35. F

    GDP and Well-Being: A More Comprehensive Measure of Economic Progress

    Hello all Here is an article about GDP and well-being: Well-being and GDP: why we need them both The general idea is something like this: GDP is a fine measure for material wealth, but well-being needs more than just material wealth like social and environmental factors. So we need them...
  36. F

    Is the Book's Photon Calculation Off by a Factor of 1000?

    Part a) is correct, but the book gives me an answer of 2.3*10^{23} for part b. Is the book wrong or have I missed a factor of 1000 somewhere?
  37. B

    Engineering Calculate 3ph short circuit symmetrical fault, per unit method.

    Homework Statement Calculate the three-phase short-circuit fault currents flowing into all five busbars. Homework Equations MVA base = 150MVA All base voltages were set to the local busbar voltages. Formulas I have used can be seen in the attached photos. The Attempt at a...
  38. A

    Drude theory: Probablity of collision of electron per second

    The Drude theory assumes the probability that an electron makes a collsion in a second with probabilty 1/ζ where ζ is the relaxation time. Since ζ can be any positive number, the probability can get greater than 1. What does this mean?
  39. S

    Interference pattern calculations for unequal slits per QM theory

    I am trying to understand how QM theory (wave-functions) are applied to Interference pattern calculations for unequal slits for a single particle double slit experiment case 1: both slits are equidistant from the "center", however one slit is bigger and the ratio of the width between the slits...
  40. K

    Notation of permittivity in farads per meter question

    I am using an old textbook as a reference, and the equation given for the electrical permittivity of free space ε0 is given in terms of: (Fm-1) where this measurement notation represents farads per meter. Why the superscript of -1 in the notation?
  41. tsuwal

    Studying Finding Best Books for Engineering Students at IST Lisbon

    I'm a Engineering student at "Instituto Superior Tecnico" in Lisbon (it's capital), renowned in Portugal for being its best engineering school. I have a hard time finding the best books in each subject since the bibliography is very extensive most of the times, or the teacher just chooses his or...
  42. V

    Electrostatic energy per e- for an alkali metal

    I'm trying to think about what it is I should be considering before I start throwing up some maths. I'm thinking to assume that the positively charged core is a point charge +e and the electron is uniformly distributed over a sphere of radius Rs. The self energy of the electron...
  43. B

    Maximum population for 2000 Kcal per day

    Dear physics, I'm new to the site. I found it reading this topic: https://www.physicsforums.com/showthread.php?t=145043 I wonder if we could manage to answer, if some not critical precision, the question of: How many people can live confortably, eating only potatos, in earth? As of...
  44. Q

    Photon Flux per Unit Wavelength

    Hi How do you get a photon flux per unit wavelength curve for solar radiation? My understanding of "per unit wavelength" is that the wavelengths within a very short range are fired at a detector. The range is then gradually changed to cover higher wavelengths. The values of flux measured by...
  45. Z

    Energy E in total per level, or per state in level?

    I'm working on a problem concerning energy levels in a 3D box. I have calculated the energy levels in eV using the standard equation: En = { { ∏^2 (h-bar)^2 } / 2ma^2 } (n^2 + n^2 + n^2) Are these calculated energy levels the total energy per level? Or does the energy E calculated...
  46. I

    Calculating volume flow rate per unit width of a plate ( Fluid Mechanics )

    This is the question The flow of a fluid between two large flat parallel plates normal to the y direction is fully developed and steady. The plates are a distance 2h apart in the y direction and the velocity profile, assuming y=0 is at the midpoint between the plate is V(y) = V_0(1-(y/h)^2)...
  47. E

    Weight of water from molecular mass to grams per cubic centimeter

    I’ve been scratching my head (and working in ms excel) about the following for about 6 hours and would greatly appreciate it if somebody could help me. Basically, I am trying to figure out WHY the density of water is approximately one gram per cubic centimeter (at 1 atm pressure and 4 degrees...
  48. L

    Find Max Potential Energy per Unit Length of Wire

    Homework Statement A wire is fixed at both ends vibrating fundamentally. For what value of x (x position on the wire, with 0 being one edge and L being the other) is the potential energy per unit length has the maximum value? Known: Length of wire (L), Tension in wire (T), Mass of wire (m)...
  49. D

    Archived Estimate nuclear energy generation rate (formula given) per unit MASS MASS?

    Homework Statement Consider energy generation in the Sun. Fusion through the pp cycle takes place within its core which has r = 0.2 Rs T = 1.3 x 10 ^ 7 K rho (density) = 1.1 x 10 ^ 5 kg m^-3 X (total mass fraction of hydrogen) = 0.34 The nuclear energy generation rate for the pp...
  50. A

    How to convert decibel micro volt per meter?

    anyone know how to convert decibel micro volt per meter to dbm?this term are using for rf electromagnet...tq..
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