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# Questions tagged [power]

The time rate of change of energy

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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 ...
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 ...
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 ...
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 ...
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?
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 ...
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) ...
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 ...
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 ...
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 ...
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 ...
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 ...
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
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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.
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.
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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....
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 (...
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 ...
112 views