Questions tagged [power]
The time rate of change of energy
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How fast do you need to travel downwind to obtain the maximum amount of power from the wind?
Suppose you are traveling downwind, in a wind speed of $x$ meters per second. If you are stationary, the wind speed relative to you will be the highest, but you will not be moving, so no work/power is ...
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Are $U^2/R$ and $I^2*R$ the same? [duplicate]
We know from Ohm's law that $U^2/R$ and $I^2*R$ are equal.
Generally, high-voltage transmission is used to save electricity.
When calculating the amount of heat generated in this case in terms of $I$, ...
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Electric power transfer
I'm reading electric power from the book "Fundamentals of physics textbook by Robert Resnick" and I have a question about the interpretation of the text.
First it says "The principle of ...
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Is energy and work the same in numerical basis? [duplicate]
Consider this formula:
P=W/t
where p is power, W is work, and t stands for time.
and also this formula:
E=Pt ,
where E is energy, P is power, and t is time.
so by the substitution property, you can ...
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Power Number of Impellers in non-Newtonian fluids
I have been working on a project involving mixing a non-Newtonian fluid.
To begin with, the fluid exhibits a shear-thinning behaviour that follows the power law:
$$\tau = K \dot{\gamma}^n$$
As for the ...
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Doubling up on Ear Protection NRR Equation
I'm planning to go to shooting ranges soon, and am looking for ear protection.
Let's say that I get an earmuff with a noise rating reduction (NRR) of $X\ \textrm{dB}$ and earplugs with $Y\ \textrm{dB}$...
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Understand power rating in layman terms
I have recently started the chapter of electricity of class 8. I am not understanding the concept of power rating of appliances. When we say that a bulb is rated 220V-100W, which means, according to ...
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What is the solar radiative power on a clear sky day through a surface which is parallel to the sun's incidence on Earth?
Assuming that the solar power through the incident surface is known. How can we calculate or estimate the radiation through the parallel surface assuming a clear sky?
Looking for watts per square ...
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What is electromotive force? What's its relationship to Voltage? + clarification of confusion
So first of all, yeah I know that the electromotive force is not a force (the name was coined by Alessandro Volta I think).
About Power and dissipated power
The power with wich a battery provides the ...
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Output of ventilator and air friction
Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
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Radiation power emmited by a material with two different temperatures [closed]
Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
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How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?
Suppose I have two rails and a wire connecting them I'd like to accelerate. Then $\frac{d\phi}{dt}=Bvl$, where $B$ is the magnetic field strength where the wire is, $v$ is the velocity, and $l$ is the ...
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Why is radiation power defined at infinity?
According to Griffiths in chapter 11 , given a source of radiation enclosed by a sphere, the power passing through the sphere is
$$ P(r) = \oint \mathbf{S} \cdot d\mathbf{a} = \frac{1}{\mu_0} \oint (...
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Why is the general unit for energy (in terms of energy bills) $\rm kWh$? [closed]
Why is the unit for energy (in terms of energy bills) expressed as $$\text{time} \cdot \frac{\text{energy}}{\text{time}}$$ rather than just energy?
Wouldn't it be better to express it in megajoules (...
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How is power dissipated proportion to current and current squared?
$P=IV$ and $P=I^2R$. Does this mean that $P$ is proportional to both $I$ and $I^2$? I don't understand this concept. And when should I use the various formulas for power? When another variable is ...
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Efficiency of thermal (rankine) power plants based on ambient temperature?
so I'm preparing for an interview and this is a common question that they always ask,
Say there are two power plants working on ideal rankine cycle
One in Alaska (low ambient temperature) and one in ...
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Time average of product of 2 function with same frequency
Hi I'm Reading a notebook on "light atom interactions"
There is this calculation I don't understand of average power -
$$P=\overline{-\boldsymbol{E} \cdot \frac{\mathrm{d} D}{\mathrm{~d} t}}=...
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Calculating the efficiency of a solar cell based on the wattage of the lamp powering it [closed]
I am working to characterize some solar cells I have access to based on their material structure by measuring the IV curve of the cells. I can generally compare the cells by comparing their $P_{max-...
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Power-time graphs for constant speed [closed]
i. What does the power-time graph for a car moving on a horizontal road at constant speed look like? Is it a horizontal line because the car engine is supplying a constant power, or is it zero because ...
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The car has maximum power, why not maximum force?
Suppose a car is moving up an inclined plane, it experiences resistive force proportional to its mass and square of speed. First, it carries a cart of twice its mass up an inclined plane and it can ...
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Bulb glows full brightness at which time of $I$-$t$ graph? [closed]
I know that for first question,resistance increases..
In second question,it is asked to find the power when bulb glows at full brightness,
I think it is NOT 1A*200V=200w
What i think is that,we should ...
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Difference between working at a constant rate and exerting a constant force [closed]
Let's assume that two trains of equal masses are moving along parallel paths. The engine of train 1 exerts a constant force, and the engine of train 2 works at a constant rate. If in time $t$ they ...
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Why does the power loss in transmission cable increase when resistance is increased?
In transmission cables, why does power loss increase when length of conductor is increased? According to the formulas V=IR and P=I²R, When we increase the length, the resistance increases, while the ...
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Calculating mechanical power of an electrical motor
The total power of a powered drill is 850 watts (the rated value written on the drill's casing) and the current at the supply voltage of 230 volts is 3.7 amperes according to the formula $I = P/U$. ...
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Derivative of formula for battery's output power is not right
There is something about output power of battery in circuits that bothering me.
I hope you help me.
So we know the formula for power in electrical circuits is (current x voltage) or:
$$
P=IV
$$
and ...
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Why is bandwidth not centred at resonant frequency in LCR series circuit?
When we calculate lower and higher frequency such that power becomes half in LCR circuit we end up with two value.
For a complete derievation please see here.
I have copied relevant information below:
...
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Electricity: Ohm law vs Power in the Water analogy
I'm trying to understand electricity principles with the water analogy. I know this analogy is not perfect, but so far it has helped me the most.
To recap:
voltage (volt) is like water pressure
...
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Why can't take gravity = 10 why velocity is given? [closed]
What is this about? I have a question and there are two ways to solve it. One is wrong and other is right and I wanted to know why was the wrong one wrong.
What do I want to know? In the wrong ...
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Why does my 3rd method not show me that power = force dotted with velocity?
I have derived 3 expressions for the power that a force, $\vec{F}$, transfers to a body. (A) and (B) are consistent, but (C) isn't. Where have I gone wrong with (C)? EDIT: THE MISTAKE HAS NOW BEEN ...
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Is power of a battery constant?
In my question I'm neglecting the impact of discharging.
I'm trying to make sense of Watt's law: $$P=IV.$$ I always thought that the voltage and the power of a battery were constant features that ...
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What exactly is power and how does it work?
Lets say that a car engine can output a maximum power of $P$. Now initially, the car starts from rest would have zero velocity.
Now the tires start slipping and a force of $f_k = \mu mg$ will act on ...
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How much power does it take to maintain the high vacuums in advanced physics experiments?
The LIGO Gravitational-Wave Observatory and CERNs Large Hadron Collider both have some impressive ultra-high vacuum systems. For my project proposal I need to demonstrate some understanding of how ...
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How do static and rolling frictions factor into force/power needed to start and accelerate trains?
I am trying to understand how to calculate the necessary force to start moving a train and I was wondering about the roles of rolling and static friction into the equation. From several sources I read ...
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Why is the brain so "efficient"? [closed]
By efficient I mean, that why is the brain able to learn tasks, for example driving, at a much less energy cost than Machine learning models?
From a quick google search it seems like it took about 55 ...
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Energy lost in a resistor and its temperature
The power lost across a resistor is proportional to the square of the voltage drop across it. This means by increasing the voltage across the resistor, the energy lost in it in a given time grows non-...
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Air resistance due to Helium vs Air
I was reading this technical note by NASA on windage power loss in alternators. In the paper, the power loss due to fluid shear between two concentric cylinders (a rotor and a stator) is derived.
The ...
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Power delivered to a Resistor is $V^2/R$. Does size of battery matter?
I had connected a thin Resistor wire to series combination of six coin cells or to a small sized 9V battery. The wire got hot in a normal way BUT when I connected the same resistance wire to a large ...
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Would be possible to cover all the deserts with solar plates and satisfy the demand of electricity?
if we covered all the deserts with solar plates , would that be the solution to the energy crisis ?
i mean put a solar plates in ALL the deserts of the earth to harvest all solar power
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How can power be defined as the derivative of work with respect to time if work is not a function?
In thermodynamics, it is frequently said that work and heat are path functions with inexact differentials $\delta Q$, $\delta W$, so one can not talk about a change in work or a change in heat since ...
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Why is Power in an electric circuit equal to $VI$? [closed]
Where did this formula come from? Everyone I asked just told me to substitute values of in ohms law to derive this but no one told why is power equal to voltage * current. Part of the reason for this ...
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Energy Dissipated by Damper Infinitesimal Derivation
If we consider a damper (dashpot) element that exerts a force opposite the direction of motion proportional to the velocity, i.e. $$ \vec{F} = -c \vec{v}$$
Therefore, we can consider an infinitesimal ...
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Power from CNO Cycle Fusion
There are all sorts of projects trying to get power from fusion reactions.
The best known and funded are the Tokamaks, big expensive crush Deuterium and Tritium (He3 sometimes) plasmas and spew ...
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Is power through a surface Lorentz invariant?
I am trying to solve this problem from Griffiths, but my point is not really to ask the answer of this problem :
A point charge $q$ is moving velocity $v$ parallel to $x$ axis. determine the total ...
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Why do we only consider tension pointing toward one direction when deriving the power of wave on a wire?
How about the tension pointing in the opposite direction? Does it not contribute to the work done by wave to make the wire move up and down too?
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Can the brakes of a Semi-trailer truck overcome the torque of the engine? [closed]
On the average Semi-trailer truck, assuming an average load, can the engine overcome the brakes and continue spinning the wheels despite the operator applying the brakes fully?
This would be assuming ...
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$I²R$ loss in case of transformer
Suppose we have a 100 V A.C. supply, and we connect a 1 ohm resistor with it. Now the current through the resistor will be 100 A. Now we connect a 1:2 step up transformer with the A.C supply, and then ...
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Why are partial derivatives of Energy and Co-Energy with respect to x opposite numbers?
In a system where the flux linkage $\lambda = \lambda(x, i)$ is a function of dispalcement $x$ and current $i$.
Its energy is defined as
$$
W = \int_{0}^{\lambda} i(\lambda', x)d\lambda'.
$$
Its co-...
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The Curie Temperature Motor Conundrum
Suppose we have a special motor with a rotor made of nickel. The shape of the rotor is such that it has a high surface area for exchanging heat with an applied flame or with a stream of cooling water. ...
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Distance-velocity relation for a body accelerated with constant power
A body of mass $m$ starting from rest from the origin ($x(0)=0$ and $v(0)=0$ at $t=0$) moves along the x-axis under the influence of a force $F$ that exerts a constant power $P$.
Question: How to find ...
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Why is virtual velocity defined with only variation in generalized velocities?
Jourdain's principle employed in Vehicle Dynamics (Road Vehicle Dynamics, Georg Rill) states that virtual power of $k$ rigid bodies vanishes, i.e.
$$ \sum\limits_1^k \delta v_i(y,z)\cdot F_i^c(y,z) + \...
