Questions tagged [power]

The time rate of change of energy

Filter by
Sorted by
Tagged with
-5 votes
0 answers
39 views

Inverse Square Law Two Formulas [closed]

I read two formulas: $$\frac{p}{4 \pi r^2}$$ and $$p \frac{1}{d^2}$$ I don't understand. I do have my own guesses but I want to know so I'm not wrong.
0 votes
1 answer
19 views

If the rotational speed of a turbine at a power plant doubles, does its voltage, current or power double? [closed]

Somehow, I cannot find a simple answer to this question, or a simple equation or equations... All other things being equal, if a turbine at your local power plant instantaneously doubles its rpm (or, ...
  • 3,735
0 votes
0 answers
11 views

Would it be possible to create a spherical csp that uses a solar array to direct light into a sphere where it can reflect back into itself?

I’m just a student who can’t find any answer about this. Perhaps because I didn’t look hard enough, regardless I’m curious. Concentrated solar power is a really big step towards solar energy. Using an ...
0 votes
1 answer
20 views

Would it be possible to extract/filter out two waves of different power but same frequency?

If we can use say Fourier Transform to extract every individual frequency on a signal, can we do the same for power? I was figuring if it would be possible to extract them for further inspection on ...
  • 1
0 votes
2 answers
67 views

Relationship between work and potential energy

Ultimately what I am trying to do here is convince myself that the following relationship holds: $$F = -\frac{dU}{dx}$$ for a force $F$ and a potential function $U$. We have that the work $W$ can be ...
  • 494
0 votes
3 answers
47 views

Calculate power for a non-constant force [closed]

Suppose there is a body of mass $m$ in a horizontal plane, with initial velocity $v_0$, that is subjected to a force $F(t)$ (the force depends on time). How can I calculate the power developed by the ...
0 votes
1 answer
54 views

What is the angular velocity of a wheel as a function of time as it is spun up by a DC motor?

For the sake of concreteness, let us consider a brushed DC motor. I am trying to predict how much a wheel spins up when it is connected to a DC motor for a certain amount of time $t$. Let's say I ...
1 vote
0 answers
50 views

What is the work done in lifting the bucket? [closed]

A bucket is tied to a well with a chain 20 meters long to lift water. If the weight of the chain is 2 kg per meter and the weight of the bucket filled with water is 20 kg, what is the work done in ...
0 votes
0 answers
26 views

Does the resolution of a timeseries affect the estimate of the power-spectrum?

I have been trying to estimate the power spectrum of a timeseries using fourier transform. I noticed that by downsampling my timeseries I get a different spectrum as shown below Here you can see ...
  • 450
0 votes
1 answer
25 views

Actual power consumption of an irregular measure (GPU/CPU) [closed]

Hello and my apologies if this is off-topic or really too basic. My math and physic days are really far far away.... I want to measure the energy consumption of both the GPU and CPU of a computer ...
0 votes
1 answer
70 views

tGiven a propulsion system with constant power, how long does it take to travel a given distance in space? (non-rel. and relativistic)

Suppose a space ship of mass $m$ is travelling away from our solar system, starting with "starting speed" $v_{start} > v_{escape\ \odot}$, meaning it will escape sun and have some ...
  • 34
0 votes
0 answers
27 views

What is the dependence of fusion power of the particle energy at fixed pressure?

The fusion reaction power depends on the reaction rate. The reaction rate depends on the concentration and the cross section.The cross section depends on the energy of the particles or temperature. ...
  • 69
1 vote
1 answer
94 views

Transformers in Power transmission [duplicate]

Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
0 votes
2 answers
35 views

How to calculate the energy and power of the force of lift that acts on a cruising plane?

Say we have a plane flying at constant speed and altitude. Looking at the y axis, the lift cancels out the force of gravity as it maintains constant height. I want to calculate the energy used to ...
  • 1
0 votes
0 answers
23 views

Reflection of power at low frequencies?

Assume you have an AC signal source outputting 0dBm of power and connected to that are two resistors one of 50 ohms and another 100 ohms. The reflection coefficient is given by: It seems like this ...
0 votes
2 answers
70 views

'Distanceless' force for aircraft seems to break laws of physics

When an jet is flying, its engines produce thrust. I assume that the thrust and fuel consumption is about the same at all aircraft speeds. However, when the airplane is going faster, it produces more ...
1 vote
0 answers
28 views

Calculate uphill efficiency on different gears [closed]

I was interested to find whether it would be more efficient to climb a hill on a lower gear, so I did some calculations. I have the following data of a custom vehicle: Gear Drive force (N) Max speed (...
1 vote
0 answers
27 views

What is the maximum possible averge power of the geomagnetic electric generator?

Earth's magnetic field strength varies from 25 to 65 μT on the surface. Therefore, magnetic energy is approximately $V\frac{1}{2} \frac{B^2}{\mu\mu_0} \approx 10^{\left (17,5\cdots 18,5 \right )} \...
  • 69
0 votes
2 answers
56 views

Calculating the rate of heat dissipation in a tungsten filament

The formula for the rate of heat dissipation in a resistor is iR^2 for an Ohmic resistor. If this Ohmic resistor is replaced with a tungsten filament, which has a resistance that varies linearly with ...
  • 43
0 votes
2 answers
39 views

An electric motor operates on a 50 V supply and a current of 12 A. If the efficiency of the motor is 30% what is the resistance of winding of motor? [closed]

This is not a textbook question,i want to understand why it would generate two different values? and I cannot do that without invoking some form of numerical value in my question Ok so I get that the ...
  • 31
1 vote
0 answers
27 views

What was the first use/cite of "Watt's law"?

Yesterday I saw a reference to Watt's law being used for the power formula P = V I. It's been over 40 years since I learned my basic electrical engineering fundamentals and this is the first time that ...
0 votes
0 answers
33 views

Solar Cell Power

I'm interested in doing a rough approximation for a solar cell efficiency under different input spectrums. I know the EQE of the cell and the IV curve under AM1.5 conditions (easy to find online). I ...
  • 649
0 votes
0 answers
4 views

What is the nature of $V$ in the wind power equation relative to wind and its dependence on being attached to a vehicle?

I've not taken many physics classes so parts of my question might be uneducated/misinformed. But suppose you have a small wind turbine attached to a vehicle. We have the wind power equation. $$P = 0.5\...
8 votes
1 answer
2k views

Why isn't Neptunium used in nuclear power plants?

The elements on either side of neptunium (uranium and plutonium) are, of course, widely used in both power plants and nuclear weapons. So why isn't the highly fissile nuclide Np-237 used in reactors? ...
  • 3,735
1 vote
2 answers
100 views

How does DC circuit deliver energy?

I don't understand how energy is being transferred in a DC circuit. For example here I have a simple circuit powered by a constant voltage. Some form of energy is being transferred from the source to ...
  • 337
1 vote
0 answers
44 views

Square coil circuit and variable magnetic field problem

I am attempting to solve the following problem. A square coil of side $l = 40.6 \ cm$ and resistor $R = 95.5 \ \Omega$ is contained within the $xy$ plane. Within the same region a magnetic field, ...
0 votes
2 answers
45 views

What goes on in an AC circuit when the power delivered to the inductor is negative?

The instantaneous power delivered to a resistor by an alternating voltage source $v(t)=V_0\sin\omega t$, is always nonnegative. But the instantaneous power delivered to an inductor by $v(t)=V_0\sin\...
1 vote
0 answers
40 views

Relation between Radiance and Surface power density (i.e poynting vector intensity)

I am attending a microwave remote sensing course and I have same problem to understand the relation between the radiance and the intensity of poynting's vector. The radiance is defined as: $L(\theta,\...
1 vote
1 answer
43 views

Electric Power of Displacement Current

Say we have displacement current $I_d$ inside a plate capacitor of alternating voltage $V(t)$. We use the formula for electric power on the displacement current: $P=I_dV$ What does $P$ account for? ...
  • 297
0 votes
0 answers
29 views

What will be the power if I add two laser with different wavelength at same power?

I am trying to combine two lasers at 960nm and 1310nm wavelengths respectively with same power 150mW by using four wave mixing. I am planning to use a 3dB coupler for adding. I just want to know will ...
1 vote
3 answers
101 views

Finding the power

A car of 1200 kg acquires a velocity of $ 25$ m/s from rest in 8 seconds. What amount of power should be given to car by the engine? Procedure-1 Work done, \begin{align} W= \frac{1}{2}mv^2- \frac{1}{...
3 votes
0 answers
60 views

How exactly can we shake an object to determine its mass?

It's often said that inertial mass is a measure of how hard it is to shake an object (as distinct from gravitational mass, which is how hard it is to lift an object in a gravitational field). Because ...
0 votes
1 answer
23 views

Can this laser cofiguration be used to penetrate armoured bodies?

I asked the same question before but as it was stated as unclear I hope that with several corrections the question is more clear now. As the question is more theoretical than engineering I posted here....
  • 415
20 votes
7 answers
5k views

Why is it impossible for the reactor of the nuclear power plant to turn into an explosive nuclear bomb?

Is it true that both work on the same principle of operation: the interactive fission chain reaction 235U/239Pu and the bombardment of uranium-235 by fast neutrons produce a fission chain reaction ...
's user avatar
0 votes
1 answer
60 views

Electric Power and Energy [closed]

I was asked a question three times this week and I have been giving the same explanation over and over again, but I am starting to question myself. if you have data on a PV panel production in the ...
0 votes
0 answers
17 views

Why the General Lomb-Scargle results are doubled?

I got a problem when computing the GLS on MATLAB for my master deegree thesis. I need to do a comparison between the PSD and amplitude spectrum of a signal computed with three different metods, the ...
0 votes
0 answers
32 views

How to convert volt-second data into power-frequency domain?

guys, I am new to physics. Due to my project, I have to utilize my data in the frequency domain. However, my data is in the time domain. So I wanted to ask how I can transform my Volt-time domain data ...
0 votes
2 answers
32 views

Why power of engine must be equal to power of friction?

Suppose a car with electrical engine moves uniformly with friction between wheels and the ground (neglect air resistance, energy loss, etc.). So why the car's engine power must be equal to friction's ...
0 votes
1 answer
56 views

Gear Ratio And Torque Relationship

suppose a gear teeth ratio of (1:10) >> then it is obvious that the smaller gear will be faster than the larger gear >> And the higher gear has more torque which means a higher ...
0 votes
0 answers
24 views

Why is the friction in the motor wrong as an answer to wasted energy in this question?

I do not understand why the answer to part b)ii) cannot be energy lost to friction within the motor as the work done by the motor should be the total work done to move the cyclist and should include a ...
0 votes
0 answers
56 views

How to find external surface temperature with unknown heat transfer coefficient?

I am trying to calculate the thickness of insulation required for a certain design. The known properties are the inside temperature, target surface temperature and thermal conductivity. From what I ...
0 votes
0 answers
12 views

What happens to electron, when we join two solar panel in parallel

When we add two solar panels in parallel then voltage will remain same but current will increase but what exactly happen to the electrons when current increases but voltage remains the same. Also when ...
1 vote
2 answers
89 views

What is the difference between antenna input impedance and its radiation resistance?

I got to know that the input impedance of the halfwave dipole antenna is given as: $Z_{in}$=1/$I_m$* sin($\beta$(H-|Z|)) where $I_m$ is the maximum current on the antenna( when excited with a 1 volt ...
  • 97
-1 votes
3 answers
52 views

Which type of star is most effective for solar power?

I'm working on a worldbuilding game, and the subject of stars has come up. Imagine you're a species, chilling in the Goldilocks zone of some alien planet, orbiting an alien star. Your people stumble ...
0 votes
2 answers
163 views

The Resistance in an electric kettle [closed]

I have an electric kettle with two parallel heating elements, both with resistance $R_0=2\,\Omega $. Both can be independently shut on and off. There is also another resistor with resistance $R$. Upon ...
  • 11
5 votes
4 answers
1k views

Does a receiving antenna radiate the power received?

Let's consider the case of linear dipole antenna or Hertz dipole. I know that the antenna acts as a transducer and it radiates the E-M waves due to the acceleration and decelaration of the electrons ...
  • 97
0 votes
2 answers
48 views

This question is about motor power requirements

If I have a motor that has a power of 20 kilowatts, does that mean that the motor can produce a torque of 10k newtonmeters at 2 rpm, or analogously a torque of 2 newtonmeters at 10k rpm since the ...
0 votes
1 answer
50 views

Gas stoves are specified in terms of BTUs. Why not units of power? [duplicate]

If you go to buy a new gas stove for your kitchen, you will note the main spec of interest is the BTU rating of the burner. Isn't industry making a mistake in using the BTU? The BTU is a unit of ...
  • 181
8 votes
10 answers
1k views

Why is Power = Voltage $\times$ Current?

So P = I*V because V is the amount of energy per coulomb and I is the amount of electrons going past a cross sectional area in one second. So if we do the math, since V = J/C and I = C/sec, if we ...
  • 181
0 votes
1 answer
53 views

Electrical Power and stored power

The simple circuit below, consists of a battery with constant electromotive force (efm), $\epsilon_0$, a capacitor which capacity varies with time $C(t)$ and ,to make it simple, ideal wires (zero ...
  • 881

1
2 3 4 5
19