# Questions tagged [power]

The time rate of change of energy

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376 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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### 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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### 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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### 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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### 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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### 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 ...
176 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Calculating the power loss from a ultrasonic welding assembly

I am tuning an ultrasonic assembly for a welding application and tuned the system to operate at 41kHz according to the oscilloscope. The transducer operates at 40kHz and 50W, when calculating the gain ...
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### 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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### 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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### 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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### 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 ...
56 views

### Finding force exerted on a turbine blade by water flow

I am trying to find the maximum theoretical rotational power of a turbine from the following quantities: $\omega$, $r$, $\gamma$, $I$, and $t$. This is in an experimental setting, not an assignment,...
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### How to calculate minimum optical power required from datasheet of camera sensor?

How can I determine from the datasheet of a camera sensor the minimum optical power required to see a spot on the image? I have 2 lasers with a diameter of 0.35 mm with respectively a power of 12nW/...
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### Adding a capacitor in parallel improves power factor of an inductive circuit?

I know that to reduce power loss during transmission, we require a power factor as close to one as possible. This can be done by making $Z$ tend to $R$ which can be done by increasing $X_c$ such that ...
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### Electrical vs Heating Insulation

Let's say we have a 120V cable and a 600V cable, this means that the 600V needs more electrical insulation to prevent the insulator from exceeding its dielectric strength. But in the other case, the ...
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### Is the force from an engine constant as a vehicle reaches top speed?

I've come across a textbook question and I've got myself confused by it although it seems like it should be simple. The van accelerates with a (supposedly) constant resistance force up to its top ...
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### Power dissipated through bulb decreases to a steady value

The instant at which bulb is switched on, its power is maximum, then it decreases to a steady value. This can be explained by the increasing resistance due to heating of the filament. (P = V*2*/R). ...
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### How much heat energy is generated by the Sun and Moon's gravitational action on the Earth?

How much heat energy is generated by the Sun and Moon's gravitational action on the Earth? It would seem fairly obvious that any spinning body orbiting a massive object will convert its own motion ...
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### Calculating Laser Focal Power & Focused Beam Waist

If I focus a 1 watt, 405nm laser with a 25mm fl lens what is the power at the waist. I see calculators online but none that make sense. Rather than just telling me can you put your equations you use ...
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### Why didn't my Capactive Wireless Power Transfer work?

Today I had the delight of setting up a bipolar capactive wireless power transfer (CWPT) circuit for a school experiment. Disappointingly, it did not work. It was set up just like in the diagram ...
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### Capacitor, stored energy versus reactive power

When an AC voltage U is put onto a loss less capacitor C the capacitor will require a certain reactive power Q (current 90 degress out of phase with the voltage): $Q=UI = \omega C U^2$ in VAr (Only ...
My question is " A locomotive engine draws a load $m$ pounds up an inclined plane making angle $a$ with horizontal, the coefficient of friction being $k$ . If starting from rest and moving ...