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Questions tagged [power]

The time rate of change of energy

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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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1answer
47 views

Black body radiation net power emitted

I have a question related to a definition (intuitive understanding). It is stated that : The human body radiates energy as infrared light. The net power radiated is the difference between the ...
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1answer
130 views

Is the net power of an open system always equal to zero?

Are the following statements, line of reasoning all correct? I'm particularly interested in the last bullet. For a closed system energy is conserved and constant. For an open system energy is not ...
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2answers
204 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
52 views

Can a tunnel through a planet be used as a power generator?

Assuming that it were possible to do so, if a tunnel from one side of a planet to the other were lined with copper wire, could dropping magnets down the hole be used to generate power?
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52 views

Can emissivity value be 4?

We know I=p/A and I=uc which I is radiation density , P is total radiation power , A is surface area and u is energy density. By putting A in the other side we will have p=ucA since energy density is ...
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1answer
87 views

Tidal Power Gen Multiplier? [closed]

Regarding tidal power generation, the following scheme uses an outer tank and an inner tank that floats on the water of the inner tank. You fill the inner tank first (while it's at high-tide level) ...
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1answer
79 views

Why is beam forming more energy efficient than a straight up omnidirectional signal?

Someone tried to explain the process of beam forming to me, and how beam forming is far more efficient than an omnidirectional signal of similar amplitude. This seemed obvious at the time: the power ...
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1answer
114 views

When and how do we use the formula Power = force X velocity?

I'm unable to understand the solution given in this book mine... Why are we adding the resistive force? In fact, i would really appreciate if someone explains the question to me, I'm really struggling ...
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2answers
120 views

Power in 1st Gear

The max power an engine puts out is what determines the max speed a car travel at right, obviously it's more nuanced than that because there are losses in the drive train, and the shape of the car ...
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1answer
116 views

Power in series

I knew that power of two resistors in series is equal to $$\frac{P_1P_2}{P_1+P_2}$$ where $P_1$ and $P_2$ are the individual powers of the two resistors. I tried to prove it using $P=I^{2}R$ and I ...
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1answer
89 views

A Pump is spraying water to form a fountain

This is a three part question. I have answered two of them. “A pump is spraying water into the air to form a fountain. The water emerges vertically from a jet of cross-sectional area 2.0*10^-4 m^2 ...
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3answers
191 views

Does density of light power (w/m²) increase after passing a convex lens ?

Does density of light power (w/m²) increase after passing a convex lens ? and if so i need the equation that represent that increase
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1answer
45 views

predicting light loss in fiber optic strand

Background: I'm working with fiber optics and I'd like to try to calculate the change of perceived brightness of visible light due to signal attenuation in a segment of fiber optic cable, based on ...
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2answers
307 views

Propulsive Power, Thrust and Velocity

If my rocket requires thrust $T$ to maintain a velocity $v$, the propulsive power can be calculated using $$P=Tv$$ Assuming the same friction (so the required thrust to maintain the velocity doesn't ...
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1answer
77 views

How to calculate acceleration from power and weight? [closed]

Imagine a bike that is not moving initially at $t=t_0$. The bike and its cyclist have a combined mass of $m=60\,\mathrm{kg}$. If the cyclist starts to apply $p=100\,\mathrm{W}$ of power, then what ...
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3answers
152 views

Power dissipated, different formulas, zero resitatance

Power dissipated on an electrical element can be given by: $$P = VI = I^2R = \frac{V^2}{R}.$$ When we have a battery with zero internal resistance, it means that the power it provides (or the power ...
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1answer
40 views

Photon energy and power

My question has to do with the solar spectrum. I understand sunlight is composed of light of different wavelegnths, and these wavelegnths have different energies associated with them. I also ...
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2answers
140 views

In the electrical circuit/fluid analogy is there an analogy for power loss across a fluid resistance?

For the fundamental passive $RLC$ electrical circuit, analogies are often used to describe the physics of fluid flow where $L$ represents the inertance analogous to inductance, $C$ is compliance ...
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147 views

why this perpetual motion engine does not work and does not break the law of energy conservation?

I came-up with this idea when i was 10 years old , I am not claiming that it is working , I just want to know why it doesnt if it doesnt ? This engine is supposed to produce infinate energy from ...
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2answers
52 views

An engines power is 650kW and the shuttle's speed increases from 120 m/s to 160 m/s in t seconds [closed]

note sure if I'm missing something obvious, but i cant seem to find a good way to tackle this question. A space shuttel of mass 400kg is moving in a straight line where there is no resistance. the ...
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1answer
41 views

Doubt between power consumption and flow of current

Suppose we have two electrical element say A and B where A having greater resistance than B , So here we say that power consumption of A is greater than B ,but when they are connected to seperate ...
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1answer
68 views

Does a fan draw the same amount of power when using it at different speeds?

Does a fan draw the same amount of power when using it at different speeds? Some of the people around me say so. But ${\rm power} = \frac {V^2}R$, and $V$ (the voltage) is always the same in the ...
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3answers
63 views

Could a vacuum provide exponential power?

A vacuum requires little power to be created and when spread over a large surface area can lift thousands of pounds. Is there a way to generate enough work out of this to create more power than was ...
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2answers
49 views

Representing electricity as electrons

Just a thought I had, I was wondering if there was a practical way to do this: Electricity is represented in Watts per Hour, and obviously, electricity is the flow of electrons. Is it possible to ...
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40 views

How to convert average horse power?

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 ...
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1answer
167 views

Temperature of 100w bulb [duplicate]

What is the running temperature of a 100w bulb if it's resistance while on is 50 ohms and the mains voltage is 240 V RMS.
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2answers
80 views

Is 220 V, 50 A equally dangerous for a person as 1A, 11000 V? [duplicate]

The question is self-explanatory. I'm a high school student so feel free to use scientific terms.
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2answers
474 views

Is there an RMS value for power delivered to an inductor?

My textbook defines power delivered to an inductor as: $$P= V_{L\rm\ peak}I_{\rm peak} \cos ( \omega t) \sin( \omega t)$$ where $\omega$ is angular frequency. but makes no mention of $P_{RMS}$. It ...
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3answers
715 views

How should I think about voltage and power?

I have been extremely confused about exactly how to think about voltage (and power) when it comes to circuit analysis. In physics, voltage is just described as the energy required to move a unit ...
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4answers
180 views

For a car engine, why does velocity increase as force decreases?

Take the equation P = FV For a fixed power of an engine, applying a greater force gives a smaller velocity while a smaller force gives a greater velocity. To me this sounds counter-intuitive. I ...
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2answers
255 views

Conducting ring free-falling in a variable magnetic field

Consider a free-falling conducting ring oriented horizontally to Earth's surface. It then enters a region with magnetic field $B = B_o(1+\lambda z)$ where $+z$ is the vertical direction upwards. By ...
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137 views

How is radiance conserved? - Power/intensity misconception

Before getting to the main question I'd like to clear some pretty basic concepts regarding energy/power/intensity as my physics is pretty rusty. According to wiki In radiometry, radiant flux or ...
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1answer
51 views

mechanical power in moving coordinate system

Suppose I have an object resting on top of a table. There are two forces acting on the object: gravitational pull and the supporting force from the table. It is pretty obvious, that the table is doing ...
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0answers
34 views

How to increase power in a geared system using P = (omega)(torque)

Could someone give me a basic, intuitive explanation on how to increase power in a geared system using the P = omega*torque formula? By geared system I mean two connected gears, where the first one ...
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1answer
64 views

Is there a way to express stream power for an entire watershed?

Fluvial geomorphologists describe stream power, $\Omega$, as the 'rate of energy dissipation against the bed and banks of a river per unit downstream length'. It is expressed as a function of water ...
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1answer
101 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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1answer
30 views

what does the “T” really represent in the signal power equation

In the signal power equation $$ P(g(t)) = \lim _{T\to \infty }{\frac{\left(\int_{-\frac{T}{2}}^{\frac{T}{2}}g\left(t \right)^2dt\ \right)}{T}} $$ What does the $T$ really represent ? From my ...
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31 views

What is the sound power produced at a defined frequency by a woofer of given diameter and excursion?

Assuming an infinitely rigid woofer of a given diameter and oscillating with a given excursion at a given frequency, what is the SPL (sound pressure level) at 1 m distance? I found https://en....
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0answers
483 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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0answers
45 views

How to determine the best fit battery for a battery powered application? [closed]

This is an attempt to get some scientific information about how to best use batteries (I'm going to refer to both single cells or assemblies of cells as batteries for the sake of this question) in ...
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1answer
112 views

Question about Power lost in a wire given voltage and current

The question is as follows: A high-voltage transmission line carries $1000 \mathrm{\,A}$ at $700 \mathrm{\,kV}$ for a distance of $100 \mathrm{\,miles}$. If the resistance per length of the wire is $0....
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1answer
35 views

How is it that a single transmission line can be modeled by a two port network?

I am studying electric power distribution. I've read in Kirtley's Electric Power Principles (2010) that a transmission line can be modeled by the 'pi' model. Which is a two port network with series ...
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1answer
857 views

What does the Force in the equation P=FV represent?

So this is the question in context. A car of mass 1200 kg tows a trailer of mass 300 kg along a straight horizontal road. The resistance to motion is modeled as being a constant force of magnitude ...
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1answer
1k views

How to calculate the power produced by a single cylinder petrol (car) engine at a certain rpm? [closed]

I want to know: What are the main parameters that make power/torque generated by engines different and what makes some engines more efficient? (except friction and things like that!) How do I ...
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1answer
563 views

Measuring voltage output of a Wimshurst machine

I see that there are a few variables that effect the voltage output of the Wimshurst machine. For one the size of the disk, the amount of conductive strips on the disk, and obviously the spark gap ...
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1answer
131 views

What are some good analogies about electrical power? [closed]

What are some good analogies about electrical power? I understand the mathematical part of $P=VI$, but I would like to somehow visualize it in a practical electric circuit.
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0answers
138 views

Building a CO2 laser power supply [closed]

So i bought a 15,000 volt franceformer for $160. This is used to power my CO2 laser that is also homemade. The power supply is the most expensive part by a landslide so I decided to ask around. I ...
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2answers
2k views

Can power (in the context of work and energy) ever be negative?

Consider this question which HAS definitely been asked but i ask you now to question your first inclination to just 'do the question' and explain the thought process. Restrictions: assume you only ...
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1answer
25 views

How do microwave transformers avoid power loss through the skin effect?

I was reading about the skin effect and how the effect increases for higher frequencies. I also read that Litz wires can be used to counteract the effect, but usually only up 1 Mhz frequency. Is ...