Questions tagged [power]

The time rate of change of energy

579 questions
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Does the brightness/power of each individual bulb change when you add more bulbs in a parallel circuit?

I have asked this question on different sites and have received contradictory answers. Assume that there is an ideal voltage source and the resistance of each bulb is the same. I believe that the ...
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Why is the lamp with the lower power rating brighter in the series circuit?

If I have two lamps, both of them have different power values, and voltage value is constant , I've been told that the lamp that has less power would be brighter and make more light than the lamp that ...
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Power in a uniform circular motion

I've a circular motion and I want to find the power that the motion is generating. The formula's I got: $$\text{P}\left(t\right)=\text{W}'\left(t\right)=\text{E}'\left(t\right)$$ Where $\text{P}$ is ...
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Relationship Between Watts and Candela

I am currently working on a project that involves the use of LEDs. According to the datasheet, the LEDs I am using have a maximum brightness of 10,000 mcd. In my project, though, I will not be using ...
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Are large scale optical power delivery systems feasible?

I am attending an introductory course of optics and photonics and we just started to study optical fibers for digital communications. However, I have started wondering about using optical fibers to ...
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AC vs DC & why we ended up using AC for power in our homes, etc [duplicate]

I think that DC is better than AC (and yes I do have a reason, check the comments). Also, if it (DC) is in-fact better than AC why did we use AC then?
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Rotational Power/Energy Mismatch

My question is pretty fundamental but has me stumped. Long story short I can't seem to calculate the correct required power to accelerate a mass to a set speed in a set distance. Every time I ...
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Why power dissipated over a resistor relies upon intensity not upon voltage

For computing the power dissipated over a resistor the correct formula is $P = R \times I^2$. Why, in other purposes equivalent, $P = \frac{V^2}{R}$ is not good? I can imagine that the actual current ...
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When do these equations apply in electrical circuits and when do they not?

My textbook tells me that in order to calculate the power (in watts) for an electrical circuit then the equation is $P=VI$ (volts times amps equals watts). However, I have read online that this ...
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Transformer vs Inductor for lighting a bulb or any other appliance

There was a question in my school physics exam which is as follows: Consider a 100W bulb which operates at 50V dc. John wants to light this bulb by a 200V ac source. What component should he use, ...
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Definition of Power from electricity and from energy

In the electricity topic, my physics book has defined Power as $P=IV$, $I$ being current and $V$ as voltage. But then later in the Energy topic, power has been defined as $P=\frac{W}{t}=\frac{F.d}{t}$...
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Velocity vs time curve of negatively accelerating motor

I have a hopefully interesting yet simple question. I want to plot the velocity vs time curve of a motor decelerating. The interesting bit is that the acceleration is going to be directly connected ...
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Does it make sense to compare mechanical wattages to electrical wattages?

A smartphone might produce 1 watt of power. A voltage of 1 volt producing 1 ampere of current over 1 second is 1 watt of power. (Did I do that right?) Or a kid pushing a toy block might produce 1 ...
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Impact force of a pillow?

My friend and I just had a discussion about how dangerous it would be to get hit in the face with a pillow thrown out of a train. If we say the train is traveling at 100km/h and the pillows weight is ...
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How could this small nuclear reactor power two jet engines?

In the 1950s, the US was working on an Aircraft Nuclear Propulsion and it is stated that they successfuly operated two modified General Electric J47 jet engines using a 2.5 MW (thermal) nuclear ...
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What do I measure with power meter?

I modulate directly a laser diode by setting the pump current periodically from 0 A to $I_{on}$ A. I do it for different duty cycles and different frequencies. But I need to keep my average power of ...
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Finding out how long a light bulb will light [closed]

A cylindrical wire used to form a light bulb filament has radius 3.7 micrometers and length 1.7 cm. The resistivity of the wire is 5.25 * 10^-5 ohm meters. The light bulb is connected to a 12V battery....
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Can global warming be exploited as a useable energy source? [closed]

I saw an Internet video about global warming, specifically how well the comedic giant ice cube idea could actually work. But then I thought about (other) science-fiction cartoons in the future. How ...
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What is the physical meaning of the zeroth component of the Minkowski force 4-vector?

In David Griffiths' Intro to Electrodynamics, section on ED and relativity, he poses a simple problem regarding the zeroth component of the Minkowski force 4-vector for a charge $q$ moving with ...
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How much heat can be adsorbed in a solar parabolic trough?

How do I know the produced heat on the focal point of a solar parabolic trough per different radius if made from steel and also from glass?
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How much power and energy is (actually) in a 230 dB “click” from a whale?

In the BBC Science in Action podcast the acoustic power of a 1 millisecond "click" from a whale was said to be 230 dB. The related BBC article mentions this number and elaborates: The blue whale is ...
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Can the intensity of a sound wave in a minimum be greater than intensity in a maximum?

Suppose to have two speakers $A$ and $B$ one in front of the other, producing coherent sound waves with the same frequency $f$ and power $P$. In different positions on the line connecting the speakers ...
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Predicting top speed of a flywheel [duplicate]

I connect a DC motor to a flywheel with a given moment of inertia. I then supply that motor with a constant voltage and current for an infinite time interval. What do I need to know about my motor to ...
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Won't the Power be dissipated in the first quadrant of this graph?

In the following picture: In the first quadrant of the V-I graph(for an Independent Current Source, where the voltage supplied is positive on the top) won't the power be dissipated instead of being ...
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Could an infinite spinning windmill create endless electricity? [closed]

This is not so much a question about if this idea is physically possibly, but more a question of if it was possible. If a magnet could somehow push a windmill around at a constant speed continuously, ...
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Bernoulli equation and pumps [closed]

I have a doubt on the use of Bernoulli equation for pumps. Consider the situation in the picture. I marked different points: $1$ on the surface of first tank, $2$ in the exit from first tank, $3$ ...
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Elementary derivation of $P = UI$ starting from the definition of voltage as work done per unit charge

Consider the following elementary derivation of the formula $P = VI$ for Joule heating of a resistor $R$ for the dissipated power $P$ where the voltage over the resistor is $V$ and the current $I$. ...
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Geometric frustration in power transmission networks

I'm confused about pumps in fluid dynamics. As far as I understand, the basic effect of a pump which deliver a power $\mathcal{P}$ can be described with modified bernoulli equation between a point $A$...