Questions tagged [power]
The time rate of change of energy
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Help me understand power and torque [closed]
I'm trying to understand power and torque relationship in terms of cars.
Let's assume we have a four tracks with a load that needs a total of 1000N to move.
First one has 1000 Nm and 1000W
Second ...
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Power dissipated in a circuit
If total power dissipated in a DC circuit is given by $P = VI$ and power dissipated as heat is given by $P=I^2R$, since these are numerically equal, wouldn’t that mean all the power is dissipated as ...
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What happens to laser power when resonator cavity length increased?
I am working with a He-Ne laser. What I have noticed, is that when resonator cavity length is increased (by moving on of the mirrors), output power goes down. What could be an explanation to that? ...
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Average of calculated quantity of discrete data
Let's say I have two discrete series of a physical quantity, current I and voltage V taken at the same time interval in a DC circuit. Now, I want to estimate the average power P over N measurements, ...
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Spectral representation of a white stationary process
I am trying to better understand the spectral representation of stochastic processes. From the book "Spectral Analysis for physical applications" by Walden and Persival:
The spectral ...
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Why can't I balance the units in the equation for power of a sound wave?
According to this answer (source), the time averaged power $P$ of an acoustic wave is:
$$P = \frac{1}{2} \mu v \omega^2 A^2$$
Where $\mu$ is mass density of the medium, $v$ is speed of sound in the ...
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Does $Power=F\cdot V$ imply $K.E=mv^2$?
The work done on a body with mass is equal to the constant force applied on the mass, multiplied by the distance over which that force is applied ($W = Fd$). Dividing both sides by the time over which ...
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How can heat generation be $V*I$ when the total power available to a circuit is $V*I$?
If joules law says rate of heat generation in a circuit is $V*I$, but the total power available to a circuit is also $V*I$, then all power in a circuit must go to heat. How can this be possible if a ...
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What does stand behind the formula: "watt = ampere * volt"?
I know the "watt = ampere * volt" formula, but I don't understand what it means.
So, let's start from the beginning.
Coulomb answers the question: how many electrons do you have (in a ...
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Power equation in transmission lines [duplicate]
In transmission lines we increase the power to "reduce energy loss in the form of heat". Can someone explain exactly how and also I understand that we have to keep our power constant ...
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Calculating the power received by a pixel from a set of rays
I've written a path tracer and am now working on implementing a physically accurate way of simulating the actual sensor response for a given wavelength$^*$, given an exposure time, aperture size, ...
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Can radio waves with multiple frequencies have the same power?
I was watching data from a spectrum analyzer that shows the frequency of the wave and its power in dBm. I noticed that all frequencies were operating at the same power; however, I don't understand how ...
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Finding the relation between powers from $V$-$I$ graph
Clearly, resistance of A is greater than that of B. So, my teacher told me, Heat is directly proportional to resistance, hence, the answer is A. However, what I thought was heat is indeed directly ...
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Cause non-linear relation between intensity and photo-current
I wanted to investigate and validate the relationship between intensity and photo-current with a simple experimental setup. I expected a linear relationship based on the photo-diode's datasheet (I've ...
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Power when work is 0
Imagine a rocket of mass m that is at a constant altitude. Gas velocity v. It is necessary to find the power P of the engine. I have a problem: to find the power, you need to divide the work by the ...
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Understanding the CMB power spectrum 02
I've read many posts, books, articles and so on about the CMB power spectrum (this page for example http://background.uchicago.edu/~whu/intermediate/map5.html) to try to understand it, but I seem to ...
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Why don't we have underground thermal power plants? [closed]
I learned from wikipedia that for the production of electricity, the temperature of geothermal sources must be at least 150 degrees Celsius.
Also wiki says that at a depth of 6 kilometers, the ...
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How to understand power propagation speed? [duplicate]
When reading papers, I am confused with power propagation speed of acoustic wave in fluid. The problem is given below.
For a plane, acoustic wave with pressure
$p_i(x,y,t)=Ae^{j(\omega t-kx\sin\theta+...
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Why engine power is not equal to the kinetic energy produced by the engine per second?
There is an engine pumping liquid, for example, water, through a pipe. One way to figure out the engine's power is to times the force with the velocity of the liquid. The other way is to calculate the ...
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Car acceleration limit: friction vs. power
I am currently trying to understand a certain relation between power $P$, velocity $v$ and acceleration $a$.
We are looking at a car driving along a horizontal road and at static friction, and how ...
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Simulated nuclear blast using electric arcs
"Nuclear bombs" have some distinct associated phenomena. They produce loud bangs. They produce bright flashes of light. They produce bursts of gamma radiation.
These phenomena are diagnostic ...
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Voltage drop due to large amount of current in Parallel circuit
There is this one particular thing I don't understand. I was going through the text book exercise and found this question.
What happens if the machine being driven by the motor jams, so that the ...
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Why retarded time doesn't matter in Larmor's formula? [closed]
There's a usually way to deduce Larmor's formula,
$$P = \frac{\mu_{0}q^{2}a^{2}}{6\pi c}$$
It starts with the fact that the Poynting vector is $\vec S= \frac{1}{\mu_{0}}\vec E \times \vec B$, and ...
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What's the proportion of energy received on an overloaded generator?
I'm trying to understand the underlying physics with how generators work. I found this question which had some interesting answers, but it does not include all the details I'm after.
Suppose I have a ...
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Mechanics of ''Sumo'' vs Conventional Deadlift
A classic strength move (called the deadlift) involves bending over a heavy bar, holding it in one's hands, and then pulling it off the floor and standing up straight.
Recently a variant called ''sumo ...
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Relation between input electrical power and output mechanical power of DC motor
I am trying to understand how to calculate the mechanical power output of a DC motor. My thinking is as follows.
I believe that the power input should equal to the mechanical power output plus some ...
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Power Consumption vs. Energy Consumption [closed]
I want to ask a question about power vs energy. I am a freshman & currently writing my first research project. It involve in creating an efficient energy device. I have tested my device and it ...
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"Why do power lines use high voltage?" Loss in power equal to Current*Voltage? [duplicate]
I define P is the average power. So $P=IV$ and $I=\frac{P}{V}$.
$P_{loss}$ I define to be the power loss, which is equal to $I^2R$.
Substituting for $I$, $P_{loss} = \frac {P^2R}{V^2}$
So I get that ...
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How does the thrust force change when putting propellers inline with each other?
If you have two propellers on the same axis with the thrust force in the same direction as each other, how would this change the total force?
If two (for argument's sake) electric motors are facing ...
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Calculations about vacuum chamber heat pipes
Heat pipes, as seen in many laptops and computers are used for transferring the heat of the CPU to the fans.
On my house boat, I have a stove at one end. The other end could do with heating up too. I ...
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Velocity in power calculations in different inertial frames
In calculating power using the formula $\underline{F}\cdot\underline{v}$, what is the correct velocity to use? Does one use the velocity of the body on which the force is acting, or the velocity of ...
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Hollow conductor for transmission line
A hollow conductor can transfer almost the same current when compared to a solid conductor with less material requirement due to the skin effect. But still, we use solid stranded conductors for a ...
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Heat generated and heat dissipated in electric circuits
Why formula for heat generated in electric circuit is H= i^2Rt,
While formula for heat dissipation in circuit is H= i^2R
Shouldn't these be same as all the generated heat is dissipated eventually?
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Windmill in an open circuit
I have a question for which I did not find any relevant answer on the web.
What happens to the kinetic energy of a rotating windmill if the windmill is not connected to any power line, that is if the ...
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Mechanical power during rotational motion and torque: the physical meaning of their time derivatives
It is known that the mechanical power during rotational motion is defined as:
$P = M \cdot \dot{\theta}$
where $M$ is torque ($N \cdot m$) and $\dot{\theta}$ is angular velocity ($rad/s$).
If we ...
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Does higher Hertz mean a higher electric bill?
Suppose my electric utility is meant to provide power at 60 hertz, but instead it provides it at 61 hertz. Would my electric bill be higher? Assume I run the same appliances for the same amount of ...
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What does the $R$ in the formula $P=V^2/R$ for power represent?
We know the following formula:
$$P=V^2/R.$$
I want to ask what the $R$ in the above formula represents. Is it the normal resistance of the resistor (load) or is it the increased resistance of the ...
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Getting Energy consumed by using the Gradient of the Power
My goal is to predict the energy consumption in Wh over a time window by using the current power draw and the current gradient of this power draw. In other words, if my power usage is increasing at ...
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If the rotational speed of a turbine at a power plant doubles, does its voltage, current or power double? [closed]
Somehow, I cannot find a simple answer to this question, or a simple equation or equations...
All other things being equal, if a turbine at your local power plant instantaneously doubles its rpm (or, ...
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Would it be possible to create a spherical csp that uses a solar array to direct light into a sphere where it can reflect back into itself?
I’m just a student who can’t find any answer about this. Perhaps because I didn’t look hard enough, regardless I’m curious. Concentrated solar power is a really big step towards solar energy. Using an ...
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Would it be possible to extract/filter out two waves of different power but same frequency?
If we can use say Fourier Transform to extract every individual frequency on a signal, can we do the same for power?
I was figuring if it would be possible to extract them for further inspection on ...
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Relationship between work and potential energy
Ultimately what I am trying to do here is convince myself that the following relationship holds:
$$F = -\frac{dU}{dx}$$
for a force $F$ and a potential function $U$. We have that the work $W$ can be ...
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Calculate power for a non-constant force [closed]
Suppose there is a body of mass $m$ in a horizontal plane, with initial velocity $v_0$, that is subjected to a force $F(t)$ (the force depends on time). How can I calculate the power developed by the ...
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What is the angular velocity of a wheel as a function of time as it is spun up by a DC motor?
For the sake of concreteness, let us consider a brushed DC motor. I am trying to predict how much a wheel spins up when it is connected to a DC motor for a certain amount of time $t$. Let's say I ...
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What is the work done in lifting the bucket? [closed]
A bucket is tied to a well with a chain 20 meters long to lift water. If the weight of the chain is 2 kg per meter and the weight of the bucket filled with water is 20 kg, what is the work done in ...
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Does the resolution of a timeseries affect the estimate of the power-spectrum?
I have been trying to estimate the power spectrum of a timeseries using fourier transform.
I noticed that by downsampling my timeseries I get a different spectrum as shown below
Here you can see ...
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Actual power consumption of an irregular measure (GPU/CPU) [closed]
Hello and my apologies if this is off-topic or really too basic. My math and physic days are really far far away....
I want to measure the energy consumption of both the GPU and CPU of a computer ...
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tGiven a propulsion system with constant power, how long does it take to travel a given distance in space? (non-rel. and relativistic)
Suppose a space ship of mass $m$ is travelling away from our solar system, starting with "starting speed" $v_{start} > v_{escape\ \odot}$, meaning it will escape sun and have some ...
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What is the dependence of fusion power of the particle energy at fixed pressure?
The fusion reaction power depends on the reaction rate. The reaction rate depends on the concentration and the cross section.The cross section depends on the energy of the particles or temperature. ...
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Transformers in Power transmission [duplicate]
Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
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