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Questions tagged [power]

The time rate of change of energy

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Power generating

I have been wondering if I can generate power from magnetic fields from electrical grid lines. If I can make an inductor to cut through the waves to power small gadgets. Our communication masts ...
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32 views

How do I find the amount of power a resistor is dissipating in a simple circuit? [on hold]

I am stuck on a physics problem where all I know is the amount of power that is dissipated by one of the resistors that is in parallel with another. The following is a diagram: All I know is that ...
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22 views

Heating effect of fast neutrons in Fast Breeder Reactors

Do fast neutrons play effective(meaningful) role in heating up the water in Fast Breeder Reactors? If so, how much do they?
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42 views

Power by normal force

Would the power created by the normal force always be zero? Since normal force is always perpendicular to the object?
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Does gravity matter when calculating work done horizontally?

My teacher gave the following question: A 212lb running back can complete the 40yd dash in 4.53s. What time would a 198lb running back have to post in order to be more powerful? My teacher says that ...
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Converting Wattage to Temperature [closed]

Let us say you have an 8 watt source or heater, what is the highest temperature it can attain or be converted to? I was asking in the context of transformer losses. At no-load, there is core loss.....
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24 views

Why didn't my Capactive Wireless Power Transfer work?

Today I had the delight of setting up a bipolar capactive wireless power transfer (CWPT) circuit for a school experiment. Disappointingly, it did not work. It was set up just like in the diagram ...
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27 views

How to calculate the power required by a fountain pump?

How can I calculate the power required by a fountain pump, if just the efficiency of the pump, the height of the fountain and the diameter of the water jet is given?
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58 views

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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Can the Earth's magnetic field used to generate electicity? [duplicate]

can we produce a voltage through earth's magnetic field by using a system containing materials having high permeability like permalloy(100000)and supermalloy(800000). From $$ε=Blv$$ $$B=4×10^{-5}\ \rm ...
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407 views

Why doesn't using more appliances at home decrease the electricity bill? [closed]

I know that at home the electric circuits are parallel, and this explains why if one appliance (eg bulb) fails, everything else continues to work, but if more devices are added in parallel to each ...
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22 views

Power Dissipation in Internal Resistance of a cell in a circuit with varying resistance

In the circuit , the battery has an e.m.f. of 3.00V and an internal resistance r. R is a variable resistor. The resistance of the ammeter is negligible and the voltmeter has an infinite resistance. ...
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24 views

Capacitor, stored energy versus reactive power

When an AC voltage U is put onto a loss less capacitor C the capacitor will require a certain reactive power Q (current 90 degress out of phase with the voltage): $Q=UI = \omega C U^2$ in VAr (Only ...
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Dependency of temperature acquired by a resistor on power

A nichrome heating element across 230V supply consumes 1.5kW of power and heats up to 750*C. A tungsten bulb across the same supply operates at a much higher temperature of 1600*C in order to emit ...
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1answer
40 views

How can only 2 phases of a 3 phase power system be used to power a load?

When looking at 2 of the 3 phases on a graph, there's a point where they're both positive or both negative. How does one of the phases act as a return path?
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75 views

Does the depth that the accelerator pedal is depressed correspond more closely to the force or the power that the engine delivers to a car?

Consider a car that only moves directly forward without turning (so that we can model its trajectory as motion in one dimension), and assume we can neglect both air resistance and the frictional ...
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26 views

Relationship between speed and power in wind/hurricanes

I was looking at hurricanes today when question crossed my mind. Cat 1 Hurricanes are the ones going up to 95mph. Cat 5 goes above 157 mph. That says a lot, but not all. In motors or engines, RPM ...
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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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31 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
43 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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1answer
47 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
49 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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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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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
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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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23 views

Photon Flux Density of a 1 dimensional Top Hat by 1 dimensional Gaussian Profile

I am working with a laser right now that takes a 4 mm input beam and creates a 60 um Top Hat by 10 um Gaussian when viewed through a 60 mm lens. The laser beam carries 180 mW of power and the ...
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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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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
97 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
38 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
55 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
32 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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42 views

Melting Aluminium powder with laser - Calculations

I'm trying to figure out how to calculate the necessary power of a laser for melting a thin layer of aluminium powder. I found this formula, applied to the stainless steel as example : W∙(1-R) = cm (...
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2answers
56 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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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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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
33 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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61 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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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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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
35 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
53 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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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
42 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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38 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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0answers
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Can self indution increase power consumption?

My question relays on the difference of consumption power of a coil when it's on AC and CC regime. A coild is made of copper wire with air core, aplied on it a CC current of 1 amp, a measure was ...
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24 views

What is reactive power mathematically?

How will you calculate reactive power in an inductor without the use of phasors? Voltage and Current are orthogonal in an inductor. So avg power is zero. Is reactive power the avg power taken over ...
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22 views

How to utilize power in work energy?

I'm confused as to how to set up $T_1 + U = T_2$ for this sort of problem. If I am given the constant power of a motor, and the mass of an object it is lifting, how do I find the maximum speed reached ...
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1answer
95 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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67 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.