Questions tagged [power]
The time rate of change of energy
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High voltage power lines - clarification of energy loss
I've been having a bit of trouble understanding the high-voltage power lines. If I was sending power from $A \rightarrow B$, we have:
Ohm's law $V = IR$
Power lost in the form of heat $P = I^2 R$
...
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Why isn't the product rule used in the definition of mechanical work?
Mechanical power is normally defined as $P = \mathrm{d}W/\mathrm{d}t$, and work is normally defined as $W = \vec F \cdot \vec x$. Today an undergrad pointed out a confusion he had from Griffiths' E&...
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Contradiction in Ohm's Law and relation $P=VI$
Ohm's law states that electric current is directly proportional to voltage provided that physical conditions like temperature remain constant i.e.
$$V = IR$$
On the other hand,
$$\text{Power = ...
user116688
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Why high voltage transmission lines?
This is a question which I seem to have tackled multiple times, solved each time after reading a dodgy internet explanation, then partially forgotten about and retackled half a year later. It is time ...
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How do you calculate power at the focal point of a mirror?
I'm a Mechanical Engineering student and I'm working on my senior project, so I need help. My project is about designing a solar dish having a diameter of 1.5 meters and a focal length of 60cm. so at ...
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What practical issues remain for the adoption of Thorium reactors?
From what I've read on thorium reactors, there's enormous benefit to them. Their fuel is abundant enough to power human civilization for centuries, their fission products are relatively short-lived, ...
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Why does it take so long to make a nuclear bomb?
So as I know nuclear bombs are derived from fission reactions: By providing the nucleus with enough power to trigger a chain reaction. If uranium was present why does it take so much to make a nuclear ...
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Mathematical Definition of Power [duplicate]
I am a high school student who was playing around with some equations, and I derived a formula for which cannot physically imagine.
\begin{align}
W & = \vec F \cdot \vec r
\\
\frac{dW}{dt} & = ...
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Power of water pump
Consider a water pump pushing water through a pipe:
We wish to find the energy which the water pump has to expend to keep the water flowing through the pipe. Writing Newton's second law for water ...
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Trying to understand jet engine [closed]
I'm trying to understand at a high level how a jet engine works. I want to know if the following summary I wrote is more or less accurate:
The jet compresses regular air into a combustion chamber. ...
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How does a car gain kinetic energy?
I understand that the engine delivers power to the wheels and friction from the ground causes the wheels to roll. However, given the power (work per time) at the wheels, how does that energy become ...
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How do I calculate the power consumed by a lightbulb?
I'm studying a lightbulb and its variable resistance, given by the expression:
$R(T) = Ro[1 + α(T-T_0)]$, where $R_0$ is the resistance of the lamp at $T_0$.
In this case, $R$ is not given by Ohm's ...
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Quantum Computing Power Advantages
Currently, the world's fastest supercomputer runs at 17.59 Petaflops, which consumes 9 megawatts of electricity. A qubit-based quantum computer has the potential to operate much more quickly for some ...
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Electric power transmission
If we want to transmit electic current for a long distance, we must minimize a heat that releases because of the resistanse. We cannot make a cable wide because it is expensive and it will be massive. ...
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Is it possible to build a thermoelectric nuclear power plant?
Current nuclear power plants are essentially an enhanced version of a kettle, which seems like a stupidity caused by a lack of other options. We heat the water which turns to steam which rotates the ...
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Voltage and Current in transformers
In transformers, the ratio of the voltages equals the ratio of the turns - so double the output coil's turns and the output voltage doubles. Then, in order to conserve energy, current halves.
This ...
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Why do power lines use high voltage?
I have just read that using high voltage results in low current, which limits the energy losses caused by the resistance of the wires.
What I don't understand is why it works this way. Does it have ...
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Why does the work-energy theorem need to include internal forces?
Can anyone kindly explain me why work energy theorem must also include internal forces?
The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
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Transformers: relation between their current, voltage and resistance
My current understanding
Transformers are used to step up and down voltage keeping power constant. Hence, for example, if I step up some voltage, the current will decrease in the secondary circuit.
...
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How much power and energy is (actually) in a 230 dB "click" from a whale?
In the BBC Science in Action podcast the acoustic power of a 1 millisecond "click" from a whale was said to be 230 dB. The related BBC article mentions this number and elaborates:
The blue ...
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Resistive heating - calculating how much a wire will heat up before it melts
I wanted to offer a simple model for students to work with about resistive heating.
Since $P=\frac{V^2}{R}$ we can calculate how much energy will be put into a wire over time, if we know the voltage ...
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Relation between power and energy
If I have an expression for the 'rated generator power' of a wind turbine, call it $P(t)$ how is the energy, that the wind turbine generator generate, related to the power $P(t)$?
So:
$$E(t)=\dots$$
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Car "oomph": power or torque?
Two of the most important magnitudes that characterize a car's engine are maximum power and maximum torque. How are those two magnitudes related to the sensation that the car has "oomph" or is "...
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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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What does the equation $P=\vec{F}\cdot \vec{v}$ really mean?
Let's say that we have a car travelling at a constant velocity (V) on a flat plane , let's assume that it's applied force or the force applied from its engine ( Fapp ) balances the frictional force ( ...
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Significance of the ion Hall parameter
For an ionized Helium gas, for example, MHD Hall generators rely on the mobility ratios between electrons and ions to function and produce a Hall current. As far as I can tell, intuitively, increasing ...
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Nuclear physics problem, Why do we use high weight atomic elements?
So as far as I know, nuclear fission uses high weight atomic elements to manufacture power. If the risk of runaway reactions are a major reason for not expanding this technology, why don't we use ...
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Ohmic Heating in Wires
please could someone tell me why Ohmic losses are always referred to as $I^2 R$ losses? Here is my problem. If the power coming from a power station is fixed then you can either deliver this power as ...
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Maximum power transfer proof
I have the following homework problem.
Consider a power supply with fixed emf $ε$ and internal resistance $r$ causing current in a load resistance $R$. In this problem, $R$ is fixed and $r$ is a ...
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Simulating a fan speed given power applied to it over time [closed]
I am driving a fan using a micro-controller. I want to test the micro-controller code without having fans physically attached to it so I thought I would model one programmatically.
I want to model a ...
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Intuitively, Why is Power Proportional to $I^2R$
As the resistance of a circuit goes down, the power increases because the current increases, assuming constant voltage. Why is this? I feel like resistance and current are inversely proportional, so ...
user24082
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$\rm Lux$ and $W/m^2$ relationship?
I am reading a bit about solar energy, and for my own curiosity, I would really like to know the insolation on my balcony. That could tell me how much a solar panel could produce.
Now, I don't have ...
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How big is a 1kW fire?
What is the size/scale of a wood fire that is producing 1kW?
I'd like to improve my ability to conceptualize various power scales.
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Flux linkage inside of a conductor
Can someone explain to me why the flux linkage inside of a conductor is dependent on the cross sectional area of the conductor?
My book says that d$\lambda$ = $(x/r)^2\phi$ where $\phi$ is the ...
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Should we forget fusion and focus on geothermal power? [closed]
Firstly I can say that I would love us to come up with a sustainable fusion solution. However with the latest estimates being 2050 at the earliest for an effective fusion solution and the planets ...
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Optimal speed for the water wheel
The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
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Is Ohm's law obeyed in power transmission?
We learnt in high school that according to Ohm's law $V/I=R$.
We also learnt that during power transmission in an electric line $P=VI$ and that in order to minimize loss voltage is raised. As a ...
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How many photons in a ultrafast laser pulse?
Photon has a specific wavelength $\lambda$. Imagine we created a mode-locked pulse, with $80\: \text{MHz}$ repetition rate, i.e. pulse are separated by $13\: \text{ns}$. The pulse duration is $4\: \...
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Why is the lamp with the lower power rating brighter in the series circuit?
If I have two lamps, both of them have different power values, and voltage value is constant , I've been told that the lamp that has less power would be brighter and make more light than the lamp that ...
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work done is zero if displacement of point of application of force is zero but why can't we assume forces on COM and its displacement
suppose i jump from ground then work done by normal is zero as point of application displacement is zero(work is doneby internal forces) but during the pushing part COM has upwards displacement then ...
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Could a mirror array used for thermal solar power plant double as a telescope at night?
I was looking at the Ivanpah Solar facility and it occurred to me that the large array of mirrors could double as some sort of telescope array at night. The climate in the desert would be ideal for ...
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Difference between $I^2R$ and $V^2/R$ and $VI$ for measuring power $P$
We use $I^2R$ or $V^2/R$ or $VI$ for measuring power $P$. Are all of these applicable for all circuits? I have seen in some circuit $V^2/R$ is not equal to $I^2R$. Why is that?
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How is the dot product a generalization of multiplication?
I've seen an interesting explanation for lots of what I previously thought were unmotivated definitions in Newtonian mechanics, namely that power is always defined as effort times flow. But when ...
user115153
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Derivation of the Lorentz transform of brightness ($dP/d\Omega$)
In the book 'Relativity made Relatively Easy' by A.Steane their is a derivation of the Lorentz transform of the 'brightness':
$$ \newcommand{\p}[2]{\frac{\partial #1}{\partial #2}} \newcommand{\f}[2]{...
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Why aren't (domestic) kettles insulated?
In my experience of buying and using kettles, I have come across none which are insulated.
The obvious reasons as to why it would be beneficial being that heating time would be reduced, similarly, ...
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Why is power dissipated in a circuit maximum when external resistance is equal to the internal resistance in the circuit? [closed]
[![question 24][1]][1]Suppose in a circuit the battery has emf 6V and internal resistance 3ohm. It is connected to an external resistance = R ohm. According to my ...
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How to inject the maximum acoustic power into a block of granite?
I know that we can use transducers that are glued to a surface to achieve this. If I want, for example, to have 200 watts of actual acoustic power in the audible range in the granite, is a transducer ...
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Does the 'mAh' rating of a battery have something to do with its power?
I'm curious about the 'mAh' of a battery: how can this impact the power of the battery?
I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
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Calculating the mechanical power of a water pump
Say I want to pump water from one container to another. The water levels are 3 meters apart, and I want to pump 10 litres per hour. I figure the mechanical power necessary, assuming no losses, is:
$$
...
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Does a rocket engine apply more power as the rocket's speed increases? [duplicate]
To clarify my level of knowledge, I'm a high school student all the way through AP Physics C: Mechanics.
So, let's imagine that there is a rocket travelling through the vacuum of space (ignoring ...
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