The time rate of change of energy

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33 views

Question for power and Ohm's law [on hold]

I have two questions specifically. Can the usage of Ohm's law be utilized to predict current, voltage in circuits such as parallel, complex and series? How would I explain this? How does the power ...
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3answers
43 views

How do Calories (kcal) relate to watts?

In thinking about exercise and "burning calories" it occurred to me that there should be some fairly intuitive correlation between the biological energy conversion going on in a person's body with the ...
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0answers
19 views

Power formulas? [duplicate]

Are different power formulas in circuits used for different reasons? For Example Power = V^2/R Power = I^2/R Power = VI
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0answers
29 views

Is it possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR?

I'd like to know if it is possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR (digital single lens reflex camera) mounted on tripod. Maybe, when shooting ...
-6
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0answers
51 views

Why is the proposed Hinkley Point nuclear power plant so expensive? [on hold]

The proposed dual-reactor nuclear power plant at Hinkley Point in England is projected to cost some 35 billion dollars. Why is so expensive? The linked article just says because nuclear power plants ...
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2answers
31 views

Why do people say that 'power flows' into or out of a component in an electric circuit?

Currently, I am learning about electric circuits, and how to apply the basic concepts of physics, like work and energy. But I keep running into the same phrase--on Wikipedia, my textbooks, ...
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0answers
15 views

Rankine Cycle Reheat Mass Flow Rate

Having worked through many examples on the rankine cycle both non-reheat and reheat, i just have one question. Can the mass flow rate of steam be calculated given only the data below? Boiler ...
5
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2answers
97 views

How is the dot product a generalization of multiplication?

I've seen an interesting explanation for lots of what I previously thought were unmotivated definitions in Newtonian mechanics, namely that power is always defined as effort times flow. But when ...
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0answers
17 views

Why does the Stefan-Boltzmann law work for power absorbed?

The setup is as follows: There is a body of emissivity $e$ and surface temperature $T$ whose surroundings have a temperature $T_s$ and may be assumed to be a black body. The body radiates at a ...
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2answers
57 views

Is power still consumed when we switch off the lights?

I was having heated discussion with one of my friends. We were discussing Earth Hour and its role in saving electricity, and creating awareness. He stated that even if you turn off the lights, the ...
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0answers
14 views

power of an engine with wind

I know the power of an engine to overcome air drag is $1/2 c_d ρAv^3$. If the speed of the car $25\ \mathrm{m s}^{-1}$ (relative to the ground) and it travels in opposite direction to a wind at a ...
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1answer
37 views

What exactly is average power?

This question arises due to a problem I'd been solving recently: The question was to find the average power supplied by the water over the six hour period. Now I have read this post which ...
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4answers
49 views

$ P = \frac {v^2}{R} $ derivation confusion [duplicate]

I have always had a confusion of why we use $ P = V I $ or $ P = I^2 R $ and not $ P = \frac {V^2}{R} $ for relating to power loss due to heat in high tension lines. I know there are a lot of ...
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3answers
52 views

Could we use solar energy with endothermic reactions to fight global warming? [duplicate]

Im in holidays in Malaysia and it is god damn hot. You cannot leave your hotel/car and go out. All this because of the sun. I we were to capture all the heat (solar panels, ...) would this help make ...
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1answer
23 views

Conceptual Doubt regarding the calculation of the Solar Constant

The Solar constant is the intensity of the solar radiation in the upper atmosphere. It's value is about $1400$ $Wm^{-2}$. Now we begin by stating that the Power radiated by the sun is about ...
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1answer
22 views

High Voltage Powerlines - clarification of energy loss

I've been having a bit of trouble understanding the High-Voltage powerlines. If I was sending power from $A \rightarrow B$, we have: Ohm's law $V = IR$ Power lost in the form of heat $P = I^2 R$ ...
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3answers
111 views

Power dissipation in AC RC circuit [closed]

Can anyone help me with this question? A 20 A peak-to-peak 60 Hz current passes through a 0.01 µF capacitor which is in series with a 33 Ω resistor. What is the power dissipation? I have ...
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4answers
75 views

Relationship among heat generated, power, current and voltage

Can you help me understand the relationship between current, voltage and heat generated? I tried two sets of heated gloves. One uses a battery which generates 7.4 volts x 2 amperes (14.8 watts of ...
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2answers
19 views

Opposing currents in a Ciruit

If I have two currents flowing in opposite directions in a wire where both currents are equal magnitude and their is a bulb on the same wire does the bulb light up at all or is it bright/dim ?
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1answer
14 views

In 3 three power system, can damage occurs from incorrectly connected phases?

A three phase generator, no grid involved, phase 1 connected to phase 3 on the load, and phase connected to phase 1 on load, what is going to happen?
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2answers
61 views

What is the power given by centripetal force?(in circular motion)

A particle of mass $m$ is moving in a circular path of constant radius such that the centripetal acceleration is varying with time as $a_c = k^2rt^2$ where $k$ is constant. The power given to ...
0
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1answer
22 views

How much power can nuclear power plants produce? [closed]

I looked at the power plants with the highest capacity and hydroelectric plants seem to dominate the list. Surely nuclear plants could be far more powerful? I assume they are limited because of ...
1
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1answer
45 views

What is the relation between power and photocurrent? [closed]

Question: A clean lithium surface is illuminated by 1.0 mW of light of wavelength 400 nm. The ejected photoelectrons, which have a maximum kinetic energy of 0.70eV, produce a photocurrent of 30 µA. ...
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0answers
44 views

Voltage and reactive power

Why are reactive power and voltage related? When the control system of a generator increases/decreases the current of the rotor, voltage and reactive power are increased/decreased.What is the relation ...
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3answers
68 views

If energy of a wave is proportional to frequency, why are higher-powered lightbulbs brighter?

E = hf. Got it. P = dE/dt, right? Not seeing an amplitude anywhere in the formula, so shouldn't the power rating on the lightbulb only be driven by the color? Is it a problem with the way the ...
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1answer
36 views

power in an ac circuit - difference between in series and parallel

In AC-circuits, we have different kinds of power: active power $P$, reactive power $Q$ and apparent power $|S|$. Let's say we have a circuit with a resistor $R$ and an inductor $L$. My understanding ...
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5answers
84 views

Resistance vs Power experiment - not linear relationship? [closed]

Ok, so I have been performing a lab experiment in class involving resistors. We were asked to set up 3x 47Ω resistors in 6 different combinations in a circuit with a 6V power supply. We also attached ...
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0answers
23 views

Sound frequency and power

Although I have studied physics I am not clear on this question: Given that two (or more) sound waves have the same amplitude does the power they carry depend on frequency? What about electrical AC ...
0
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3answers
71 views

$P=VI$ and $P=V^2/R$ [duplicate]

How come equation a) $P=VI$ says if you double voltage, power is doubled while according to equation b) $P=V^2/R$ says power quadruples? Which one is correct?
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1answer
26 views

Power and friction [closed]

An object moves with a constant velocity of 10m/s on a rough surface with frictional force of 50N. What is the power of the object? And why do we use force of friction instead of the force provided by ...
0
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2answers
29 views

Can an Oven being set to a different temperature cause electric board to go off?

Basically: the electrical system kept going off (when light goes down in a division due to too many electrical appliances on at a time, or their combined power consumption). My roommate said it was ...
1
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2answers
71 views

Are there alternatives to steam in thermal power stations?

'A thermal power station is a power plant in which heat energy is converted to electric power. In most of the world the prime mover is steam driven. Water is heated, turns into steam and spins a steam ...
3
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1answer
71 views

How does the energy remain conserved in a transformer?

The induced voltage in the secondary coil of a transformer is given as $\frac { { N }_{ S } }{ { N }_{ P } } *{ V }_{ P }$ (where ${ N }_{ P}$ and ${ N }_{ S }$ are the number of turns in the primary ...
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2answers
69 views

Why Neutral and Ground Wire are Thin As Compare to 3-Phase Line Wire?

in 3-phase 4-wire systems line wires are big as compare to neutral wire. as per law , so,area of neutral wire is low ,then resistance of neutral wire is high. so, heat loss is more. as per ...
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2answers
48 views

When heat loss is more than energy generated [closed]

Suppose a electric power station produces 200W of electricity @ 200V. Now instead of stepping it up, it decides to transmit it as 200V to a city 20 km away. The transmission cable has resistance per ...
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0answers
12 views

Power of solar panel and dc generator

I have made a solar stirling engine and I need to measure its power and compare it to the output power of a solar panel. I need to see which one is more efficient. I am using the same area in both ...
0
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1answer
44 views

$P=V^2/R$ confusion

I am confused on how to apply the formula $P=\frac{V^2}{R}$ If I am given a bulb say with power 60W and it is connected to a supply of 120V. Then the resistance of the bulb is 240$\Omega$ but if ...
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0answers
16 views

how to calculate Cp of wind turbine

I am having trouble calculating C$_p$ of my wind turbine The radius of my rotor blade is 4.5 inches and it's rotation per second is 10 (10 rotations per second). So I found my tip speed of blade ...
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2answers
105 views

Transformers: relation between their current, voltage and resistance

My current understanding Transformers are used to step up and down voltage keeping power constant. Hence, for example, if I step up some voltage, the current will decrease in the secondary circuit. ...
1
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1answer
110 views

Why is power dissipated in a circuit maximum when external resistance is equal to the internal resistance in the circuit? [closed]

[![question 24][1]][1]Suppose in a circuit the battery has emf 6V and internal resistance 3ohm. It is connected to an external resistance = R ohm. According to my ...
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0answers
19 views

How does it takes to deadlift a sports car? [duplicate]

In the movie Furious 7, Dom lift a Lykan HyperSport with bare hands. Given that in reality, how strong it has to be to lift a Lykan HyperSport(1,380 kg), says to 40 cm in one rear end, and hold it ...
2
votes
2answers
57 views

Why dont you take derivative of force in definition of power ? P=F.v

The derivative of work is $\bf F\cdot v .$ $$P(t)= \frac{\mathrm dW}{\mathrm dt}= \mathbf{F\cdot v}=-\frac{\mathrm dU}{\mathrm dt}\;.$$ But why not $$(\mathrm d(\mathbf F)/\mathrm dx)\cdot \mathbf x ...
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1answer
32 views

Estimate battery's real capacity in real time [duplicate]

The maximum capacity of a battery during usage can vary from manufacturer's specifications due to factors like temperatures and battery health. Because of that i want to estimate the real maximum ...
2
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0answers
26 views

Estimating the battery capacity using current power consumption and battery percentage

I want to estimate the current maximum capacity (in kWh) having the current power consumption (in kWh) and the state of charge of the battery (in %) available in a time series. I do not have a full ...
2
votes
1answer
36 views

Power vs. Speed - Indoor rowing

In the sport of indoor rowing (and probably others) I know that to double your speed you must increase your power output by a factor of eight. I am wondering why this is the case. The indoor rower ...
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1answer
37 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 ...
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0answers
29 views

How is Thermal Design Power (TDP) related to Surface Power Density (SPD)

Although this question is kind of IT related I'm interested into the actual physical backgrounds and thus posting it here. I know that TDP is an indicator for dimension of the thermal dissipation ...
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0answers
25 views

Thrust to weight [closed]

Want to put a ducted fan or shrouded propeller motor on a snowboard. How much thrust would be needed to propel 275 on a snowboard? I'm aiming for a speed between 15-25 mph. The board would be 169 cm ...
1
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1answer
41 views

Minimum Power Required to Maintain a Population Inversion

According to many sources, the minimum power required to maintain a population N in the upper level of a two level laser system is $$P_{min}=fA_{21}Nh\nu$$ where $f$ accounts for the lack of 100% ...
0
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0answers
36 views

Calculating electricity used for weights on an elevator

Given an elevator with a motor driven by a power supply, torque ability and a pulley does it take more electricity to lift more people? I have some of the calculations but do elevators lift at a set ...