Per Definition and 545 Threads

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...

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...

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...

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...

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...

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...

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...

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.

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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)...

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...

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

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...

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...

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...

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...

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...

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.

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...

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

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...

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?

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?

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...

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?

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...

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...

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...

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...

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...

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)...

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...

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)...

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...

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

Homework Statement You are in a car that is on the top of a steep 500 meter high hill. You are stepping of the brakes so your car is not moving. How much energy per second( power) must be expended to keep the car stationary Homework Equations The Attempt at a Solution

I am reading Aschroft and Mermin and I came across the probability per unit time I have trouble understanding the concept as it is. But they do try to explain. They say that the probability that an electron will experience a collision in an ifinetismal time, dt, is just dt/τ. From this i...

Homework Statement Cold-roiled steel of high silicon content enables the designer to use higher operating flux densities with lower loss per kg. The higher flux density reduces the weight per kVA. Can anyone explain how & why does weight/KVA depends on flux density Homework Equations...

Average Cost. A manufacturer has determined that the total cost $C$ of operating a factory is $C=0.5x^2+15x+5000$ where $x$ is the number of units produced. At what level of production will the average cost per unit be minimized? (The average cost per unit is $\frac{C}{x}$) taking C' and...

Hi all, Homework Statement The motor driving a large grindstone is switched off when a rotational speed of 360 rpm has been achieved. After 15s the speed has decreased to 210rpm. If the angular deceleration remains constant, how many additional revolutions does the stone make before coming to...