Questions tagged [power]

The time rate of change of energy

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11 views

Calculate the power supplied by voltage source [on hold]

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 ...
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54 views

What does this mean? World consume 14 trillion watts of power

I am not very clear about this statement. Does that mean in every second we are consuming that much energy?
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60 views

Why does current arrange itself in such a way as to minimize power loss in resistors connected in parallel?

In problem 2 in Problem Set 6, it is said: "Electricity prefers to flow in the way that minimizes energy loss to resistance." Using Lagrange multipliers I was able to show that assuming the above ...
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Why a Box moving at Constant Velocity isn't doing Work?

This was a question from an A-Level past paper and the question is pretty straightforward. I was in a hurry so I couldn't think much on this problem and chose $C$ as my answer, checked it on the ...
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1answer
46 views

Expression for net power consumed when resistances are connected in series in electric circuit

To find the expression for net power consumed, I did this :- $$ \text{Suppose some resistances } R_1, R_2, R_3, ... \text{ are connected in series in an electric circuit.} \\ \text{Let R be the ...
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Watts vs. volts amperes

What I understand: In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt I understand that a watt is a unit of power (change in energy per unit ...
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7answers
80 views

Initial speed is zero and so is power?

If I want to accelerate something from standstill to max speed, with a constant force (acceleration and mass don't change), the equation P = F * v would say that in the beginning we use 0 W power. How ...
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1answer
38 views

Power and intensity of a sound wave

So in the case of a point source of a sound wave in a sphere, I'm wondering why the Intensity decreases with $r^2$ because if i setup the formula the Power always increases with $r^2$. So these two ...
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37 views

Can the mains voltage affect laser intensity?

First of all in very new to the photonics field and i am only venturing into it because I have to troubleshoot an experiment and the issue seems to be the optics block. So i am using an instrument ...
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3answers
66 views

When high voltage leads to low current in power transmission system how its not applicable for household voltages?

When high voltage leads to low current in power transmission system using transformers,how increase in voltage in household circuits from 220 volts makes the current increase damaging the appliances, ...
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59 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 ...
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power consumption of vacuum pump

I am using the vacuum pump from KNF Neuberger Inc to create a reduced pressure environment for the dryer. I want to calculate the energy consumption of this pump. The pump is removing nitrogen gas ...
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Calculating the power loss from a ultrasonic welding assembly

I am tuning an ultrasonic assembly for a welding application and tuned the system to operate at 41kHz according to the oscilloscope. The transducer operates at 40kHz and 50W, when calculating the gain ...
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Normalizing Efficiencies with different motor power ratings

I have obtained data of the efficiencies of a few models of electric vehicles. We would like to compare them, but we have noted that the different motor power ratings may have an effect on the ...
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Emissivity not accounted for in Equilibrium Temperatures of Planets

I'm trying to understand how to calculate the Equilibrium Temperatures of Planets. This is the beginning of my working for it... However, whenever I look at external sources, (like this Princeton ...
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47 views

Can neutronic emissions be used as a power source?

The free neutron will degrade to a proton electron and anti neutrino in about 15 minutes. Assuming you could slow a beam of free neutrons sufficiently to keep the size of the reactor manageable: Is ...
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18 views

Angular Velocity of a wake

I am trying to use Blade Element Momentum Theory to run some power calculations for a turbine I built, however, I'm having trouble with one value in particular. I derived the following equation for ...
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113 views

What happens to $P = F × v$ for a car moving on a frictionless surface and in vacuum?

I'm considering a scenario in which a car with an engine capable of producing maximum power of 200 hp is moving on a frictionless surface and in vacuum. Since no work is lost due to friction or air ...
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117 views

Why does incline on treadmill burn calories faster?

So I was at the gym today, running on the treadmill, when the question hit me: If I run with the treadmill on incline, I burn more calories. Since I run at the same speed, kinetic energy is constant, ...
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Did Usain Bolt really sustain 11 horsepower of exerted power during the 100 m sprint?

I've just come across a WP article which says: "The Jamaican sprinter Usain Bolt produced a maximum of 3.5 hp (2.6 kW) 0.89 seconds into his 9.58 second 100-metre (109.4 yd) dash" Out of curiosity, I ...
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59 views

How to calculate total power generated?

I have a circuit with a piezoelectric transducer which converts mechanical energy to electrical. The ceramic is connected to a 1 Megaohm resistor and a voltmeter which reads voltage. If I want to ...
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56 views

Finding force exerted on a turbine blade by water flow

I am trying to find the maximum theoretical rotational power of a turbine from the following quantities: $\omega$, $r$, $\gamma$, $I$, and $t$. This is in an experimental setting, not an assignment,...
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How to calculate minimum optical power required from datasheet of camera sensor?

How can I determine from the datasheet of a camera sensor the minimum optical power required to see a spot on the image? I have 2 lasers with a diameter of 0.35 mm with respectively a power of 12nW/...
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Adding a capacitor in parallel improves power factor of an inductive circuit?

I know that to reduce power loss during transmission, we require a power factor as close to one as possible. This can be done by making $Z$ tend to $R$ which can be done by increasing $X_c$ such that ...
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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 ...
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How deep would you have to put a steel pole to generate enough electricity to power one LED using geothermal energy? [closed]

I was thinking about how you might grow plants inside without sunlight powered only by LEDs. But to get the energy for the LEDs, one might drill a hole down into the Earth's magma and put a steel pole....
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For a real battery, why is two identical bulbs in parrallel slightly more dim than just one in series

Image for reference: $$\begin{align} &r = 0.8\,\Omega\\ &\mathscr{E} = 1.5\,\mathrm V\\ &A = B = 6\,\Omega. \end{align}$$ The current when the switch is open, the only other resistor is ...
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64 views

Could pressure differentials be used to produce power?

There is potential energy between something like a vacuum in a container and a gas on the outside of it, or vice-versa. Could this energy be harvested in a vacuum, or close to vacuum situation like on ...
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36 views

Which law is true at the transformator?

According to Faradays law The changing flux will generate voltage in the secondary winding/circuit, so if the N2 = 2*N1, then the U2 =2*U1, and according to conservation of energy in that case I1 = 2*...
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314 views

How to determine which bulb will be the brightest in the series and parallel connection?

I stumbled upon these sentences while studying and this seems to be horribly confusing. resistance is proportional to the inverse of the power of the bulb in series connection and so the bulb with ...
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How to calculate energy (KWh) from Temperature (T),Air quality (Co2), and illumination (lux)?

I have data of temperature, air quality, and illumination.I want to calculate energy consumption (KWh) from these parameters.My data is shown in the image . Also, examples are also shown in image 2 .
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Why am I getting two answers from the same question? [closed]

In this problem, if I use the formula for power as $\frac{F\cdot s}{t}$, then the answer is 37.5 W. But if I use the formula $F\cdot v$, then the answer is 75 W. How is it possible that the man has ...
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How step-up transformers help in transmission of electrical energy over long distances?

i have read just read this blog: http://www.blueraja.com/blog/194/do-transformers-obey-ohms-law below blockquotes is taken from the blog above: We connect a 1 volt AC generator to a 1 ohm ...
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42 views

Path to ground / Source in AC circuit

I'm a 1st year EE student and i'm trying to get my head around earthing systems at the moment and could do with some help. The first thing that i'm struggling to understand is how current establishes ...
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19 views

Energy conversions due to movement of car up the slope

We know if a car is travelling at constant speed up the hill then the power output of engine is equal to change in gravitational potential energy per unit time . (Assuming friction negligible). What ...
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51 views

Power in a simple electrical circuit [closed]

In this picture, as we know power due to heating of the resistance is $V^2/R$ . Now, if we add a parallel resistance to the circuit, the power dissipated through this resistor is also $V^2/R$ ...
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1answer
103 views

Power absorbed by electron in plane electromagnetic wave

How can the power (in Watts) absorbed by the electron be calculated, knowing the incident electric field amplitude $ E_0 $, wavelength $ \lambda $, and the electron momentum relaxation time $ \tau $ ...
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Electrical vs Heating Insulation

Let's say we have a 120V cable and a 600V cable, this means that the 600V needs more electrical insulation to prevent the insulator from exceeding its dielectric strength. But in the other case, the ...
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38 views

Is the force from an engine constant as a vehicle reaches top speed?

I've come across a textbook question and I've got myself confused by it although it seems like it should be simple. The van accelerates with a (supposedly) constant resistance force up to its top ...
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189 views

Why High Voltage Power Lines need more Insulation than a low one?

"A 400 kV cable requires less insulation than a 240V cable." This was regarded as False in one of my question papers, but why? Doesn't a higher voltage means, lower current(P=V. I) and a lower ...
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Power dissipated through bulb decreases to a steady value

The instant at which bulb is switched on, its power is maximum, then it decreases to a steady value. This can be explained by the increasing resistance due to heating of the filament. (P = V*2*/R). ...
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1answer
156 views

Brightness of lamps

The brightness of the lamp (power) depends on two factors: The voltage and the current which flow through it. In Figure(A) as the variable reaistance increases its reaistance, the current which flow ...
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1answer
74 views

Force exerted by a motor, velocity, and friction

Some motor make an object move on a surface very slowly. One can write at steady state : $F_{motor}-F_{friction}=0$. The friction is supposed to come from the surface so : $F_{motor}-\mu_s m g=0$ with ...
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34 views

How can I find the power given only the torque?

I have a system where I am trying to find the power generated by a DC electric generator. However, I am not very familiar with generators, so I am having difficulty determining the rotational velocity....
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37 views

Formula for Power from Kinetic Energy

Work Done = $Fd$ Power = $Fv$ If the (net) Work Done = Change in Kinetic Energy, and the object starts from rest: Work Done = $\frac{1}{2} mv^2$ Power = $\frac{1}{2} m av$ Power = $\frac{1}{2} ...
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Mechanical and electrical power of discharging a capacitor

I want to find the power of completely discharging a capacitor with capacitance $C$ during a time interval $\Delta t$. Using the mechanical definition of power as the rate of change of energy $W$ ...
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55 views

How to estimate energy of piezo igniter discharge?

Question for fun. We all know piezo igniters, these small friends, like following one: All of them are probably quite similar: same spring, same piezo, same hit force, and so on. Also I have some ...
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The water analogy seems to imply that power = current. Why is this incorrect?

Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming ...
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Internal resistance problem

A 12V battery has an internal resistance of $2.0\Omega$. A load of variable resistance is connected across the battery and adjusted to have resistance equal to that of the internal resistance of the ...
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1answer
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Power - why do we use the driving force over the resultant force?

I'm an A-Level student, studying Further Maths. We've chosen the Further Mechanics as our optional module of the course. Further Mechanics, unfortunately, is not making a lot of sense to me, because ...