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# Questions tagged [power]

The time rate of change of energy

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89 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,...
22 views

### 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/...
102 views

### 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 ...
59 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 ...
33 views

### 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 ...
68 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 ...
41 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*...
593 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 ...
20 views

### 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 ...
92 views

### 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 ...
43 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 ...
27 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 ...
58 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 $V^2/R$ ...
118 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 $\tau$ ...
33 views

### 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 ...
57 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 ...
470 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 ...
22 views

### 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). ...
392 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 ...
107 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 ...
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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### Dependency of temperature acquired by a resistor on power

A nichrome heating element across 230V supply consumes 1.5kW of power and heats up to 750*C. A tungsten bulb across the same supply operates at a much higher temperature of 1600*C in order to emit ...
119 views

### How can only 2 phases of a 3 phase power system be used to power a load?

When looking at 2 of the 3 phases on a graph, there's a point where they're both positive or both negative. How does one of the phases act as a return path?
340 views

### Does the depth that the accelerator pedal is depressed correspond more closely to the force or the power that the engine delivers to a car?

Consider a car that only moves directly forward without turning (so that we can model its trajectory as motion in one dimension), and assume we can neglect both air resistance and the frictional ...