The time rate of change of energy

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1answer
58 views

Why are GPS transmitting signals made so weak?

Twice this year, my car's GPS receiver got totally lost. It seemed the cause of this was heavy cloud, (because I can't think of any other reason), and the GPS stayed in "Recalculating" mode, until ...
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2answers
21 views

Does a switched on power socket consume electricity? [on hold]

Lets say I have a TV and a power socket but the TV switch is off however the socket switch is switched on, so will it consume electricity?
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1answer
26 views

Formula connecting Force and Power

Is there such formula? There probably is of course, but i would like a very concise description of how to derive it, in order to better understand myself. Thank you in advance.
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0answers
26 views

Calculating the force applied by an electromagnet on a ferromagnetic object

I know how to calculate the force applied on a magnetic object by an electromagnet at $n$ metres distance using $$F = \frac{(N \cdot I)^2 \cdot k \cdot A} {2 \cdot g^2},$$ but how would one calculate ...
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0answers
37 views

Why is 1 horsepower=746 watt? [closed]

We solve a lot of problems using horsepower, where we use the conversion factor of 1 h.p. = $746 watt$. But, I want to know, from where did this value came? Is there a specific derivation for this ...
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0answers
18 views

Work done by flow of a fluid

I'm looking at the power a flow of steam when used by a turbine. I originally assumed that the kinetic energy of a moving section of steam was equal to (let $V$ be volume, $\rho$ be density, and $v$ ...
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1answer
42 views

relationship between voltage and current

I know that this question had been asked many times but I think it will be a new info in Ohm’s law: $$R = V/I$$ So Voltage is directly proportional to Current In Electric Power’s law: $$P = ...
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1answer
25 views

Power of a wave in a string

My text of physics, Gettys', shows how the energy, both kinetic and potential, of a small element $\Delta x$ of a string, through which a wave (whose wave function is $y:\mathbb{R}^2\to\mathbb{R}$, ...
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5answers
143 views

No need Power to fly ? Paradox [duplicate]

I would like to know how much power I need for magnetic levitation. $$P = Fv.$$ $F = F_g \approx \text{mass} \times 10$, okay. But $v = 0$! I can't believe I need no power to keep an object in the ...
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1answer
35 views

Which power equation to use: P = (I^2) * R or P = V^2 / R

Ideal max voltage V = 200V and max current I = 5A (these are both given) Therefore ideal resistance R = V/I = 200 /5 = 40 ohms Therefore Ideal max power P=IV = 5 * 200 = 1000W 1st power equation: P = ...
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1answer
24 views

How is power of a water pump related to amount of water delivered from pipe?

My book says: Suppose a pump motor is used to deliver water at a certain rate from a given pipe. To get n times the water from same pipe in same time the power must be increased by $n^3$ ...
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1answer
22 views

Why does power loss in pure metal caused by temperature is calculated base on $P=I^2R$ but not $\frac{U^2}{R}$

$$P=I^2R=\frac{U^2}{R}$$ The metal's resistivity is temperature dependent, neglect the change in size by temperature. The power loss of a pure metal when it drop form temperature $T_1$ to $T_2$ is ...
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4answers
116 views

How power lines use high voltages with a low current?

I've read that power lines use high voltages and low currents to reduce power loss due to resistance. Looking at the formula for power - P = VI So to increase P, you increase V rather than I for ...
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2answers
29 views

Engine fuel consumption vs power

Something that has bother me for a long time is why a 600 hp engine uses more fuel per kilometer than a 80 hp engine. Let pretend I have two equal cars (same shape same weight etc) except for the ...
18
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2answers
4k views

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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1answer
29 views

How to Calculating power using smart phone?

I'm writing a smart phone app and one of it's functions is to calculate power of the vehicle that the phone is travelling in. The user enters the total weight of the vehicle and the app uses the ...
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3answers
75 views

Calculate acceleration from power [closed]

I am currently programming a simple computer space ship simulation. This is just for fun to train my programming, 3D graphics and a little bit of physics skills. What I want is the user to pick a ...
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2answers
42 views

How to improve the power output of an AC motor without changing its characteristics [closed]

I have an AC motor at 230V/50Hz and 2.2 KW power that will power a drilling bit for cutting wood. The motor has 3000 RPM, but if I attach the drilling bit (8 cm wide, 15 cm long and with a step of 8 ...
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1answer
61 views

Can I convert Power to Force?

I just realized that I have some issues with physics: I cannot just convert Power to Force (different units), $P = F * v$. But am I not able to calculate the force on a car that accelerates with a ...
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5answers
3k views

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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0answers
46 views

Deduce v(t) from power and torque

I'd like to know if this is possible to draw the highest curve of $f : t \longmapsto v(t)$ of an accelerating car based on power and torque curves like this one (EV) or this one (TV). I assume we ...
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2answers
39 views

Relation between power & thickness of the filament

Tell me what relationship is used to solve the question given below. There are three bulbs of power 60, 100 and 20; which one has thickest filament for same source? (a) 100 (b) 20 (c) 60 ...
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1answer
28 views

Does the power of the resistor change when the battery is changed?

Wanted to know whether the changing of a battery (potential difference)affects the change of power consumption of a resistor of a bulb. please tell me how the change will occur?
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0answers
19 views

Ratio E/B and power in rectangular cavity

I would like to know if the relation $E=B*c$ still holds in a rectangular cavity Let's consider this rectangular cavity where the wave is travelling along the z direction ...
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2answers
53 views

According to calculations why the current of a battery of a mobile is high?

If you pay attention to the features of your mobile's battery the voltage would be around 3-4V and power is 4-5 Wh (14400-18000 Ws) and with calculating the current you can find a very high ...
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1answer
51 views

Converting Langley to Watts

I'm reading a really old paper which looks at estimating the surface energy fluxes for The Great Lakes. They show all of their values as Langleys per day. Can this be converted to Watts per meter ...
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1answer
57 views

Power of several focused laser beams on a small surface

After viewing this: My Homemade 40W Laser Shotgun Will the initial 40W power of the diodes beams be roughly transferred to the targeted surface where the 8 beams are focused, or will there be a power ...
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1answer
28 views

can a power supply with high voltage value and some current be split into multiple small voltages of same current?

For example: if I have a source that can give an output of 10,000 Volts with some unknown current value, now, can i make that 10,000 Volts to 50 (need not be 50 exactly but maybe more than 30) of 200 ...
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0answers
33 views

How power spectral density in time domain can be understood?

I got some data which basically gives me the variation on the time of a PSD measured across specific frequency bands ranges, for instance [10Hz-30Hz]. However I have not found any good explanation ...
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1answer
76 views

Normalizing values in dB scale

I'm doing some experiments with optical power through a glass fiber. The power is measured in dBm. For the graphs that I make (Power in dBm vs time), I normalize the values relative to the initial ...
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1answer
83 views

Free Body for object on vertical wall, Applied force, Torque required for motion [closed]

I am trying to understand how to create a correct Free Body diagram and understand formula used to forces acting on object (i.e. a robot with 4 wheels) that is "placed" on vertical surface such as a ...
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2answers
43 views

Non-linear relationship between power supplied and perceived brightness in a filament lamp?

I was expecting the relationship between these two to be linear, but after conducting an experiment my data fits almost exactly on the curve, $y = 2800.2 x^{2.0173}$, where $y$ is the brightness in ...
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2answers
91 views

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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3answers
86 views

What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?

My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
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2answers
67 views

Speed to power conversion

Here it is stated that there is a cubic relationship between fan speed and power consumption (Pfan ∝ FanSpeed^3). I have the fan speed (m/s), but I need to convert it into power (W). How can I compute ...
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1answer
72 views

Passively moving air [closed]

I'm interested in channeling air into an underground condenser to generate water. Which of these approaches would be most appropriate, and is there a better approach I haven't considered? A: A ...
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0answers
25 views

electromagnetic losses at conductor interface at high frequencies??

Skin depth effect reminder When an electromagnetic wave arrives at a conductor interface of conductivity $\sigma$ , most of it is reflected back. Only a small fraction penetrates as an evanescent ...
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2answers
73 views

Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...
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3answers
60 views

How does $p=fv$ hold when $v=0$ and an engine is working?

Standard high school equations: Work = Force x Distance Power = Work / Time = Force x Distance / Time = Force x Velocity When a space rocket takes ...
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0answers
103 views

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$\lambda$ = $\frac{x^2}{r^2}$$\phi$. Where $\phi$ ...
0
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1answer
36 views

Ratio of two RMS values in recorded audio

A quick(ish) question: I produce music and I am having a discussion on the difference between two RMS values in a specific record Nero: The Thrill (Porter Robinson Remix). In the verse, the RMS is ...
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0answers
19 views

How does one measure the power factor?

How does one measure the power factor? $$\text{power factor}\equiv\frac{\text{power}}{|V||I|}=\frac{R}{\sqrt{R^2+(1/\omega^2C^2)}}$$ for an RC circuit driven with $V(t)=V_0\cos{(\omega t)}$.
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2answers
41 views

Simple Circuits [closed]

I have a small and easy dilemma, judging by how sophisticated the website is, and need a simple answer for it So $P=E/t$. And $P=I*V$. Therefore $E/t=I*V$. I just need an explanation on how this is ...
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0answers
49 views

High resistance wire as a heating element

I'm redesigning one of the labs for our senior lab class at my university. It's a thermal conductivity experiment meant to measure aluminum's thermal conductivity in a thin (1.1 cm diameter) rod. I ...
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1answer
106 views

Find the electric field of light due to an LED [closed]

This is a JEE mains question which neither me, nor any of my teachers can figure out. Help me here. "A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the ...
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1answer
69 views

Power dissipation across resistors in series

Suppose we have a simple circuit with an input voltage source $V$ and two resistors. Now if we want to find the power dissipated by each resistor using the formula $V^2/R$, should the voltage be the ...
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0answers
30 views

Calculating power in fluid systems with $pQ.$

I was wondering: say we have a fan which is being used to provide lift to some mass, like in a simple air cushion device, where the air has to flow through a chamber beneath the fan. Let's say that ...
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1answer
33 views

General relation between power density of any engine and dissiapation rate and temperature

Many years ago ( before my university studies ) I read that renewable resources are fundamentally limited by laws of thermodynamics to produce energy very slowly (low specific power or power density) ...
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1answer
68 views

What does 400kW(e) mean?

I am trying to read a document and it says a power grid is 400kW(e) what does this mean?
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1answer
31 views

How much power does it take to keep a massive particle suspended in a gravitational field?

For instance if I have a rocket of mass $m$ in a uniform gravitational field $g$, and I want to keep it floating in the air via thrust alone, then how much power in the form of (say) chemical energy ...