The time rate of change of energy

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-5
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1answer
46 views

What is a watt? [closed]

So in class I have learned that a watt is volt * amperre. In America they have 120 volts in the switch, while in Europe we have 220-240. I have seen the same powersupplies in the Us and the Eu, which ...
0
votes
2answers
23 views

Does the effect change if a continuing and constant force acts upon a mass?

If a continuing and constant force $F$ acts upon a body with the mass $m$, does the power (work per unit time) increase over time? It would mean that the converted energy per time unit increases. Is ...
0
votes
1answer
32 views

Too many antennas around a single energy transmitting antenna?

I am not a physicist. So I am not even sure, if I am phrasing this question properly. Lets say there is a wireless transmitter transmitting energy. Let us say I place $N$ number of antennas around it ...
1
vote
1answer
55 views

How big would a Dyson swarm have to be to supply the whole earth's human population with power?

If human energy consumption per year is 150,000 Terrawatt-hours, and the energy output of the sun is about 380 Yottawatts, how much area would you need at a distance of 0.5 Astronomical unit, in order ...
0
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1answer
30 views

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second?

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second? Not exactly a physics question per say, but it falls in the realm. How do I convert/understand ...
0
votes
1answer
49 views

Calculating estimated HP from velocity, auto weight, and constant acceleration

I am working on a simulation program that runs theoretical performances of different cars and was wondering if there is a way to estimate the HP at any running RPM? the problem is (and this may be me ...
0
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1answer
32 views

Out of phase AC transmission lines in parallel

I've been reading up on power transmission networks and came across this thing. http://en.wikipedia.org/wiki/Quadrature_booster Basically it balances the load between two parallel power lines by ...
1
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3answers
79 views

Why can't unequal current sources be connected in series?

Imagine two power sources: PS-1 that can supply $5A$ at $100V$, and PS-2 can supply $10A$ at $40V$. Due to conservation of charge and Kirchoff's current law (KCL), this is incorrect, and would lead ...
1
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0answers
40 views

How big does a natural gas compressor station have to be, so as its possible explosion to produce power equal to that of a nuclear bomb [closed]

I live in Greece and a natural gas compressor station is going to be constructed within a radius of 3km. That got me wondered. Can a possible explosion produce equal power with the little boy, the ...
0
votes
1answer
46 views

Sound power radiation of two monopole sources

For a fixed given electrical power to two monopole sources, producing the same frequency. Which mode, either in-phase or out of phase, will radiate the most sound power into the far-field?
0
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1answer
25 views

Power spectral density of noise

My question is regarding power spectral density of white gaussian noise. It is known that the power spectral density of white gaussian noise is $$S_X(f)= \frac{\mathcal{N_0}}{2}$$ My question is does ...
2
votes
1answer
70 views

Why high voltage transmission lines?

This is a question which I seem to have tackled multiple times, solved each time after reading a dodgy internet explanation, then partially forgotten about and retackled half a year later. It is time ...
0
votes
1answer
43 views

If halving signal strength is only a 3db drop, why can't cell phones be much lower powered?

My phone can receive a signal that's -90dBm. That's roughly one-billionth of a milliwatt. Cutting a signal's strength in half only drops the signal by 3dBm. Apart from slightly higher range, is there ...
0
votes
2answers
52 views

Power and velocity?

If $P=Fv$, power is constant and the power is the rate of change of kinetic energy, i.e. $P = d(mv^2/2)/dt$, what must $v(t)$ be to satisfy this equation?
0
votes
1answer
35 views

Parallel Resistors (special cases formula)

1) A car's rear window defroster uses $n=15$ strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged ...
0
votes
1answer
51 views

Power - 1/2 Force x velocity? [closed]

A pump, taking water from a large reservoir, is used to spray a jet of water with speed 20m/s. The nozzle of the pipe has radius 0.05m, and is level with the surface of the reservoir (no change in ...
1
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0answers
31 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
-3
votes
1answer
70 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 ...
0
votes
4answers
31 views

High power short duration from low energy source?

1MW, can 1000Joules source of energy deliver 1M of power in 1 millisecond? $Energy =$ $P$ $x$ $t$ , so does it make sense to have small amounts of energy in large pulses of power? In an extremely ...
0
votes
1answer
40 views

Making of the electricity

I'm interested if there are actually some new electrons created in the process of Making of the electricity (turbine-generator-electricity)? I guess (flow of the electrons in the wire - electricity) ...
3
votes
1answer
424 views

Power dissipation in circuits:Why is high voltage used in power lines?

I know this question has been asked before, but there is one doubt I still cannot clear. Power dissipation is proportional to $I^2R$. Does this not mean that it is also proportional to $V^2/R$? If ...
0
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1answer
35 views

Does adding water on convex mirror increase its power?

What is the comparison between the power of convex lens in air and in water ? What causes the change in its focal length
1
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2answers
37 views

Finding power in series circuit

A resistor of resistance 12 ohms is connected in series with a cell of negligible internal resistance. The power dissipated in the resistor is P. The resistor is replaced with a resistor of resistance ...
0
votes
1answer
51 views

Getting maximum power/brightness from 5 lightbulbs with different resistances [closed]

Hi I am trying to figure out the best way to arrange 5 lightbulbs to get all of them to have the maximum brightness with a 30V battery. The 5 five lightbulbs have different resistances: 3ohms, 6ohms, ...
0
votes
2answers
140 views

What's the relation between output voltage and time to boil water given the same kettle?

An electric kettle rated 220V, 2000W needed 10 minutes to boil water when it is half filled with water in Singapore where the output voltage is 220V. Estimate the amount of time needed to do the ...
-1
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2answers
89 views

Why doesn't a resistor dissipate reactive power? [closed]

Is there a (preferably microscopic) explanation for why a resistor does not dissipate reactive power?
0
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2answers
27 views

Question about indutive loads in power system [closed]

Our home appliances are mostly resistive loads and the bill we pay for consuming power is actually real power. If we use more inductive loads at our home, will it just cause problems in power factor ...
2
votes
0answers
46 views

Calculate signal strength received by an Ultrasonic Transducer [closed]

Below is an image showing transducer A transmitting a signal with an amplitude of 3000mV, I am trying to calculate the amplitude of the signal received by transducer B in mV, I understand that there ...
2
votes
2answers
160 views

Power to suspend a mass in air

How much power is needed to suspend a mass in the air? The four parts below deal with the same problem. I post them all here, should there be some subtle things I didn't see. The textbook problem A ...
2
votes
1answer
44 views

Eddy Currents: Relationships between thickness and deceleration

This is probably a question with a very simple answer, but I want to make sure before I write too much. I'm doing an investigation on Electromagnetic fields, in particular eddy currents and how they ...
1
vote
3answers
274 views

How does Ohm's law apply to superconductors?

As radio amateurs we've all learned the various relationships of power, voltage, current and resistance as expressed in Ohm's Law. My question relates to the following simple circuit showing an ideal ...
2
votes
3answers
141 views

Will my car consume more if I plug in my laptop?

I drive a Volvo v40 with a 110hp diesel engine. It usually use 4.6L/100km. If I plug my laptop which is 85W, will this change the fuel need? If so, by how much?
0
votes
1answer
25 views

Why does the power in an inductor equal what it does?

I understand that power is that rate at which work is done and that because of this the power in an inductor is equal to $$P=\frac{d}{dt} \left(\frac12Li^2\right).$$ I also understand that the power ...
2
votes
1answer
43 views

Can a transformer transfer all power?

How can the transformer transfer exact power from primary winding to secondary winding if there are core losses, eddy current losses and hysteresis losses?
2
votes
2answers
128 views

Difference between $I^2R$ and $V^2/R$ and $VI$ for measuring power $P$

We use $I^2R$ or $V^2/R$ or $VI$ for measuring power $P$. Are all of these applicable for all circuits? I have seen in some circuit $V^2/R$ is not equal to $I^2R$. Why is that?
1
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0answers
55 views

Max speed as a function of engine power

My question started out as finding the maximum speed of a go kart, taking into account only the drag forces as force opposing the motor. I've done some investigation to find: $$ F_{drag}=\; ...
1
vote
1answer
68 views

The inverse square law of sound through solids?

We all know about the inverse square law of sound. In short the power of the wave will get evenly spread on an ever increasing spherical expansion and this will dissipate the power of the wave at a ...
1
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2answers
125 views

who will win a race between man, horse and car of same power

Other day I got into a chat with my friend on work power and energy where he asked an intelligence related question the question was like this if a race was conducted between a man a horse and a ...
2
votes
1answer
31 views

Cooling induction current generation

We know that conducting materials can be heated by electromagnetic induction. Is it possible to generate current using a cooling process?
-1
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1answer
27 views

Is watt unit depended on turbine speed

I'm new to electronics. I have a doubt. That is... Is watt unit depended on speed of turbine ? In my mind When turbine rotates fast the power in increase. Is it right ? Please help me. Thanks for ...
6
votes
3answers
197 views

Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
0
votes
0answers
11 views

Transient Stress and Piezoelectric Generators

From what I can gather, the piezoelectric effect links mechanical stress to the potential difference across a material, with a two-way relationship between the two (motor or generator). I don't know ...
1
vote
1answer
46 views

Power delivered by a plug

Ok so i know that (in the UK) the voltage of a mains supply is 230v. But when we plug a item e.g. a tv in to it what determines how much power is drawn from this supply. I presume it is the current ...
1
vote
2answers
66 views

Is battery capacity proportional to Ampere-hour in every case?

Suppose I have two batteries one inside the laptop with 2.5 AH giving a backup for around 2 hours. The battery is external inside a UPS system with 7.5 AH. Since it has thrice the capacity of the ...
-1
votes
1answer
145 views

why countries can't make nuclear bombs? [closed]

Somehow when I google about the nuclear bombs I find a lot of books and resources that seem to explain everything about how those bombs are made. But sometimes I often hear that countries that want to ...
2
votes
1answer
79 views

What exactly is three phase power? [closed]

What is three phase power? How does it differ from normal AC current?
1
vote
0answers
32 views

Energy stored in a battery?

I want to calculate the energy lost from a battery to heat, and the energy stored in a battery. Are these formula's correct? $ E_b$ = $I$$V$ x $t$ $ E_H$ = $I$$R$$^2$ x $t$ $E_b$ = energy stored in ...
2
votes
1answer
30 views

Minimum Power Required

Here is a question, I found two methods to solve it, differing in the answers and I'm not sure why a method is incorrect. Question: A fire hose of cross section area ...
1
vote
1answer
28 views

Understanding the energy transffered/used from a power source?

A source of power(from a generator,battery,etc...) is used to power a system of any kind. We can calculate the energy used via this formula $E$ = $IV$ x $t$ ? For example, a battery that is connected ...
0
votes
2answers
41 views

Question on power

A wind turbine produces a power $P$ when the wind speed is $v$. Assuming that the efficiency of the turbine is constant, the best estimate for the power produced when the wind speed becomes $2v$ is ...