Questions tagged [power]

The time rate of change of energy

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389 views

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
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124 views

What do I measure with power meter?

I modulate directly a laser diode by setting the pump current periodically from 0 A to $I_{on}$ A. I do it for different duty cycles and different frequencies. But I need to keep my average power of ...
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77 views

Geometric frustration in power transmission networks

I read this article concerning the detection of Braess Paradox on power transmission networks: http://phys.org/news/2012-10-power-grid-blackouts-braess-paradox.html Here is a quote from the article: ...
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499 views

What is the physics behind the vibrating feeling you get when you touched an inducted metal surface?

When I was last working on the highway, I stopped to help a motorist parked under high tension power lines. I'm driving a large Ford Transit van, fairly box shaped. My van was parked 90 degrees (...
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89 views

Power in a wind turbine

An wind turbine starts turning by a wind speed of $v_b$ and it stops turning (rated wind speed, to prevent overloading) by a wind speed of $v_g$. By wind speeds between $v_b<v<v_g$, the power ...
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54 views

Why does an alternator slow down when the 3 phases are shorted?

I'm designing a small wind turbine and noticed that when i short the three wires coming out of the alternator, the alternator is breaking and the blade RPM is dropping. What is the explanation for ...
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142 views

How to apply conservation of energy to active noise-cancelling headphones?

Active noise-cancelling headphones add the opposite waveforms of the ambient sound in order to cancel out this ambient sound by destructive interference. I do not understand why adding more power in ...
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183 views

Estimating the battery capacity using current power consumption and battery percentage

I want to estimate the current maximum capacity (in kWh) having the current power consumption (in kWh) and the state of charge of the battery (in %) available in a time series. I do not have a full ...
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98 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
2
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1answer
2k views

Total power consumption of electric device

For some electric devices, like a fan or air conditioner, I read about their power consumption in watts on their specification guide. Does it tell about the power at normal or full speed? or Does the ...
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2answers
37 views

Confusion in usage of formulae for power dissipated in a circuit

When should we use $\frac {V^2}{R}$ and when to use $I^2R$. Because many times they ask about the power without giving details about series and parallel. I am really confused
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1answer
44 views

Calculate Retinal irradiance (W/cm² to log photons/cm²/s)

I have been trying to calculate what retinal irradiance value I get with a 1 blue LED system. Since the manufacturer didn´t give the spectral distribution information, I will approximate LED as a ...
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48 views

Can neutronic emissions be used as a power source?

The free neutron will degrade to a proton electron and anti neutrino in about 15 minutes. Assuming you could slow a beam of free neutrons sufficiently to keep the size of the reactor manageable: Is ...
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20 views

How to calculate energy (KWh) from Temperature (T),Air quality (Co2), and illumination (lux)?

I have data of temperature, air quality, and illumination.I want to calculate energy consumption (KWh) from these parameters.My data is shown in the image . Also, examples are also shown in image 2 .
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2answers
32 views

Power factor in Transamision

What is normally the power factor in the transmssion.? Is there some standard or guidelines for that.? Also, the low factor is not desirebale as it leads to more power loss. That makes sense. They ...
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2answers
228 views

Energy consumption from acceleration

I have an interesting problem. I have a machine which has to lift 35 kg (this is the total mass of the object and the lifting arm). The lifting is done by a servo motor. Now I want to calculate the ...
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1answer
102 views

Whose electric energy consumption 'copper' or 'aluminium' element in Water heater will be greater?

Considering water of 20 litres 25 degree celsius of temperature needs to be raised. Using the heat equation q=mcpdt considering cp of water to be 4.2 kJ/kgk we get q=2100 kJ which equals 2100000 J. It ...
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2k views

How to calculate theorectical engine max. torque from max. power and RPM?

I'm trying to come up with a formula to estimate an engine's maximum torque (and at which RPM) given other values and some assumptions. I'm approximating an engine's torque curve as 2 linear ...
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3answers
54 views

Would we require energy to walk in a gravity free space?

If there was no gravity would our leg muscles lose energy to make us walk. When we walk we cover strides . when we lift our one leg from rest on ground accelerate it until it reaches top say to speed ...
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154 views

How to Calculate the total scattered radiation power and total radiation power.?

Let's suppose I have incident field $E^i_z$. The components of Scattered electric and magnetic field are $E^s_z$, $E^s_\phi$, $H^s_z$ and $H^s_\phi$. The electric and magnetic field components ...
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1answer
165 views

Power and radiance scaling in Coherent Beam Combination

Generally, it's said that for incoherent laser beam combining, the intensity scales with N (where N = # of lasers), whereas the intensity scales with $N^2$ for coherent combining. $$I_{array,...
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650 views

Sound frequency and power

Although I have studied physics I am not clear on this question: Given that two (or more) sound waves have the same amplitude does the power they carry depend on frequency? What about electrical AC ...
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65 views

Power of solar panel and dc generator

I have made a solar stirling engine and I need to measure its power and compare it to the output power of a solar panel. I need to see which one is more efficient. I am using the same area in both ...
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673 views

Luminous intensity: from Volt to Candela/m2

I use a probe for converting optical power to an electrical current. I need to convert Volt to candela/m2. The sensor, a photodiode, measure the brightness of the monitor leaning the probe on the ...
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65 views

Calculating power in fluid systems with $pQ.$

I was wondering: say we have a fan which is being used to provide lift to some mass, like in a simple air cushion device, where the air has to flow through a chamber beneath the fan. Let's say that $...
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2answers
59 views

Does the effect change if a continuing and constant force acts upon a mass?

If a continuing and constant force $F$ acts upon a body with the mass $m$, does the power (work per unit time) increase over time? It would mean that the converted energy per time unit increases. Is ...
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175 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
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618 views

Max speed as a function of engine power

My question started out as finding the maximum speed of a go kart, taking into account only the drag forces as force opposing the motor. I've done some investigation to find: $$ F_{drag}=\; \frac{\...
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1answer
44 views

Understanding the energy transffered/used from a power source?

A source of power(from a generator,battery,etc...) is used to power a system of any kind. We can calculate the energy used via this formula $E$ = $IV$ x $t$ ? For example, a battery that is connected ...
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295 views

Calculating Joule heating in magnetic field

I have problem with calculating Joule heating in alternating magnetic field perpendicular through circulate plate with radios a and height h. Lets say that alternating magnetic field is in form of ...
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102 views

How power affects heating of a coil

So I am doing a little research on my own about electronic cigarettes. Most Ecig users value high power at a standard current. This means they buy very expensive, high voltage batteries and put high ...
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51 views

Delivered/Reflected Power by Drive on a Hamiltonian System

Imagine a SHO with a drive F(t). (or in general a Hamiltonian system) What is the power delivered to the system and can we talk about the power reflected? is i am imagining say a MW oscillator ...
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1answer
98 views

How can the amplitude of the same acoustic wave be different in a interferometer?

I came up with an exercise on Halliday Resnick Krane that asked a question which consfuses me. I premit that I do not look for a solution of the exercise but for suggestions only regarding the ...
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1answer
39 views

How to show that imaginary part of complex power is reactive power?

Suppose I have a voltage across an element $V(t) = A \cos(\omega t)$ and the current through it given by $I(t) = B \cos(\omega t + \phi)$. The instantaneous power is $$P(t) = V(t)I(t) = AB \cos(\...
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9 views

What is the unit of the Angular Power Spectrum $C_\ell$ of Galaxy Clustering and Weak Lensing?

If the matter power spectrum $P_m(k,z)$ is measured in $h/Mpc^3$ and $k$ is measured in $h/Mpc$, what about its Fourier Transform $C_\ell$ and the conjugate vector to $k$, $\ell$? Thank you so much
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1answer
31 views

Power consumption of an electric circuit

In an electric circuit with a resistor of resistance R there is energy conversion to other forms. If there is just one resistor then the voltage drop over the resistor is always equal to the battery ...
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1answer
44 views

Maximizing power, current, voltage

We're asked to maximize voltage across the resistor RL, then do the same for current and power. But to find a value of R that maximizes VL, I think we'd just say infinity. And to maximize current ...
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6 views

Power absorption - ferromagnetic resonance

Magnetic energy is given by: $$ E(t) = \mathbf{M}(t)\cdot \mathbf{H}(t)$$ Hence, the magnetic power becomes: $$P(t) = \mathbf{M}(t) \cdot \frac{\mathbf{H}(t)}{dt} + \mathbf{H}(t) \cdot \frac{\mathbf{...
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1answer
51 views

Power of conveyor belt required to accelerate a mass

Assume the following scenario: A conveyor belt is driven at velocity v by a motor. Sand drops vertically onto the conveyor belt at a rate of $m$ kg/s. What is the power required to move the belt at ...
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8 views

How would you find the time taken for a steady current for a superconductor?

For part (c) I need to find the time taken for the solenoid to gain maximum magnetic field strength. However, since it uses superconducting wires, the total resistance is zero, so how would I be able ...
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33 views

Power voltage relation

I have a question concerning the relation between power and voltage. We have a lamp with power of 36W when used with 12V. With what power does the lamp work if we connect it to a 6V battery? First,...
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17 views

Fan and venturi effect

A simple calculation shows the power $P$ you can get from wind at speed $v$ passing through an area $A$ is (in Watts) $$P = 1.23\,v^3 \frac{A}{2}.$$ Using the above equation and taking the Venturi ...
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1answer
45 views

Behavior of force, velocity and acceleration when the power output becomes constant

This might look like a homework question, but really isn't. I am teaching myself some basic physics and am shamefully stuck in one place. I have designed the problem below to help myself understand ...
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1answer
29 views

Height and Velocity vertically falling body

Feynman wrote in his lecture From Newton’s Second Law we can easily tell how the object moves, and it is easy to find out how the velocity varies with time, namely, that it increases proportionally ...
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41 views

Can the mains voltage affect laser intensity?

First of all in very new to the photonics field and i am only venturing into it because I have to troubleshoot an experiment and the issue seems to be the optics block. So i am using an instrument ...
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198 views

power consumption of vacuum pump

I am using the vacuum pump from KNF Neuberger Inc to create a reduced pressure environment for the dryer. I want to calculate the energy consumption of this pump. The pump is removing nitrogen gas ...
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15 views

Normalizing Efficiencies with different motor power ratings

I have obtained data of the efficiencies of a few models of electric vehicles. We would like to compare them, but we have noted that the different motor power ratings may have an effect on the ...
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26 views

Emissivity not accounted for in Equilibrium Temperatures of Planets

I'm trying to understand how to calculate the Equilibrium Temperatures of Planets. This is the beginning of my working for it... However, whenever I look at external sources, (like this Princeton ...
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23 views

Angular Velocity of a wake

I am trying to use Blade Element Momentum Theory to run some power calculations for a turbine I built, however, I'm having trouble with one value in particular. I derived the following equation for ...
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1answer
188 views

How to calculate total power generated?

I have a circuit with a piezoelectric transducer which converts mechanical energy to electrical. The ceramic is connected to a 1 Megaohm resistor and a voltmeter which reads voltage. If I want to ...