# Questions tagged [power]

The time rate of change of energy

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### Calculate the power supplied by voltage source [closed]

Hi for this question (sorry about the picture), if the current source ($2A$) receives $20 W$ of Power, determine the $R$ of the resistor and the power of the voltage source. I sort of know I have to ...
60 views

### Power in Series and Parallel circuits

My textbooks states that the brightness of a light bulb that is connected in a circuit is determined by its power. That is, a light bulb connected in series would be brighter if it has a higher ...
83 views

### Calculating power with force as a function of time [closed]

While doing an AP question in Physics C today I answered the question differently from the professor but I'm not sure what part of my reasoning is incorrect. A $100\ \rm{kg}$ block is being pulled ...
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### 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 ...
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 ...
235 views

### Work, Energy, and Power- Hooke's Law & graphing

The purpose of the work, energy, and power lab is to demonstrate the validity of Hookes Law over a limited range of displacements, measure the spring constant of several springs, and determine the ...
47 views

### Energy Creation Using Water, Generators, and a Pump

So a friend and I are arguing over an infinite energy idea that he had about using gravity, that is an almost infinite source of energy. Water to use to push a generator by dropping and hitting the ...
26 views

### Why is the power for an object of mass m moving at a higher velocity greater than that for the same object moving at a lower velocity?

I understand the equation Fv but I will like a more intuitive answer concerning why the rate at which energy is transferred must be greater
6k views

### Why a series-wired light bulbs consume less energy than a parallel-wired light bulbs? [closed]

Why a series-wired light bulbs consume less energy than a parallel-wired light bulbs ?
102 views

### 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 ...
1k views

### How can power factor be improved by using a capacitor in an LCR circuit?

First of all what is even meant by improving power factor? My book says we can improve power factor by making impedance tend to resistance I.e. Z-》R, and then they say that power factor is improved by ...
893 views

### Nuclear to Electricity Energy Conversion

Currently nuclear power generates heat, which heats water into steam that turns conventional turbines. The energy conversion is as follows: photonic->heat->kinetic->electric This would result in low ...
508 views

I am struggling with what I think is actually a simple problem. I have an LED that emits infrared light (950 nm). It is part of a sensor system. The manufacturer claims it has a radiant power of 3000 ...
51 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 ...
54 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 ...
2k views

### If a 2,400 lb. car is moving at 1 mile per hour, how much force is required to stop its motion? [closed]

Given that I stand behind or in front of a car and someone will move the car from within at approximately 1 M.P.H., how much force is needed to stop the force driven by the engine to put the car at ...
165 views

### Electric Current Power Calculations [closed]

With regards to the equations: $P=VI$ ; $P=V^2/R$ and $P=I^2R$, if you are given $P$, $V$, $I$ and $R$ for a circuit, how do you know which equation to use? Does the use of an equation have to do ...
7k views

### What is the relationship between power and energy? [duplicate]

What is the relationship between power and energy? Of course, this is a very basic and fundamental question, but it's one that many people learning physics struggle with. I'm asking this to have a ...
298 views

### 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?
136 views

### Why we say that electrical energy is power over time p x t? [closed]

How electrical energy can be power over time when electrical energy is actually potential energy? from a lot of sources (wiki ,study.com..) comes the information that electric energy is potential or ...
163 views

### Why isn't work a logical quantity? [duplicate]

Please read till the end, before you answer. I'll start off with the examples to get to the point. Drop a block from 1 meter and it will have speed v when it reaches the ground, with total work ...
57 views

### Is it possible to create usable light from magma?

Say you drilled a hole down to the magma layer. Hot lava emits light. From what I've seen lava is red(?) hot. Then if you put some fibre optic cables down into the magma layer maybe protected at the ...
209 views

### Why does Work Done Appear to be More than 100% Energy in a System? [closed]

Energy is equivalent to the work done on a motor. The work done on the motor is multiplied by more than 100% by recycling the energy the motor uses. Why then does the energy in the system appear to be ...
1k views

### Calculating energy needed for by a car climbing a slope [closed]

I'm having a difficult time answering this question. I think I'm just converting the units wrong somewhere: You're the CEO of a courier company, and you decide to select an electric car for your ...
124 views

### How is power defined?

Isn't power defined by: $$P=\frac{dE}{dt}$$ (?) I see in all websites that power is the amount of work done per time. Is it represented only like this? Why?
606 views

### Finding the resistance of platinum wire [closed]

Im currently lost on solving this potentially simple electricty question and was wondering if anyone in this community could hint me or tell me which equations and why these equations would be ...
102 views

### Can a fusion bomb make electricity? [closed]

Would blast energy remove a single piece of pre-cut earth above an underground explosive? Could you then break apart the piece of earth and lower it back into the cavity as a way of generating power? ...
15k views

### Average Power and Instantaneous Power

I am confused between the usage of the terms average power and instantaneous power. What is the main difference between the two?
443 views

### Work, energy and power [closed]

A load of mass $m$ slides down a smooth plane with inclination title from point $A$ to $B$. The same mass is then dropped from $A$ to $C$. Could anyone decipher this $\downarrow$. I've edited the ...
57 views

### What holds good? [closed]

If the 1 ohm resistor is replaced by a 0.2 ohm resistor. what will be the current flowing through ? What actually determines it ? the OHM'S LAW or POWER CONSERVATION ?
144 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.
2k views

### Why Ohm's law is followed inside the house? [closed]

In power transmission lines, as power remains constant, according to $P=VI$, current decreases when voltage increases, thus Ohm's law is not followed. But inside our house current increases when ...