Questions tagged [power]

The time rate of change of energy

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How Much Power Is Required to Hover?

Suppose I have a spaceship that weighs 1,000 kilograms. I take it to the surface of the planet with a gravitational acceleration of 10 meters per second-squared. The planet has no atmosphere and I'm ...
254 views

Is a Microwave oven without a faraday cage a health hazard?

Microwave ovens have something of a Faraday-cage/shield to keep from leaking (emitting) EM radiation. What would happen if the shield or the door was removed? No doubt it would be less efficient as ...
334 views

Why does discharging a capacitor give a higher power output than using a battery?

Let's say you charge a capacitor with a 10V battery. The capacitor will have a potential difference (pd) of 10V once it is fully charged. If you then connect a light bulb to the capacitor, the pd ...
471 views

Does a rocket engine apply more power as the rocket's speed increases? [duplicate]

To clarify my level of knowledge, I'm a high school student all the way through AP Physics C: Mechanics. So, let's imagine that there is a rocket travelling through the vacuum of space (ignoring ...
1k views

What is the relation between Work and Power? [closed]

If I lift 40 kg 6 times 60 centimeters, is that 40*6*0,6*9,82 Joule? And then if I take the time into account, I will know the Watts? Or did I misunderstand? The background is that I read that you ...
16k 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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Won't the Power be dissipated in the first quadrant of this graph?

In the following picture: In the first quadrant of the V-I graph(for an Independent Current Source, where the voltage supplied is positive on the top) won't the power be dissipated instead of being ...
217 views

No need Power to fly ? Paradox [duplicate]

I would like to know how much power I need for magnetic levitation. $$P = Fv.$$ $F = F_g \approx \text{mass} \times 10$, okay. But $v = 0$! I can't believe I need no power to keep an object in the ...
56 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?
381 views

How to understand the thermal radiation?

I am studying the thermal radiation (StefanāBoltzmann law) by myself $$P = \epsilon \sigma A T^4$$ here $\epsilon$ is the emissivity, $\sigma$ is Stefan-Boltzmann constant, $A$ is the surface area ...
84 views

Sound intensity and space/things in the way

Suppose you have two stationary people, A and B, who are equally effective in terms of hearing ability, and A emits a sound that is heard by B at a certain intensity. If they remain stationary, and B ...
243 views

What are the properties and impediments of a liquid air fueled engine?

I recently came across a very interesting article that suggested the possibility of using liquified gases like air, nitrogen, or oxygen as a power source for cars. It appears that this company is ...
47 views

Velocity reference point when calculating power [closed]

As shown in the picture, a person (80 kg) is on a platform (20 kg) that's suspended by a rope which is on a pulley. As they pull on the other side of the rope, they reach a constant velocity of 0.4 m/...
34 views

PMDC Motor Characteristic Graph for Given Parameters

TL;DR Need to make a graph which showcases all parameters of a PMDC motor against the torque input. I am trying create a graph similar to as shown below. However, I am confused as to how the torque is ...
71 views

Complex Poynting vector and energy loss

Consider continuum medium (no boundaries) and the electromagnetic wave Poynting vector $$\mathbf{S} = \mathbf{E}\times \mathbf{H}^*$$ with $^*$ the complex conjugate. When there is a phase difference ...
37 views

Analytically understanding wireless power transfer

https://youtu.be/M8aZoM9p43k This YouTube link shows a experiment I quickly made. Two resonant lc circuits that use magnetic fields to wirelessly light up a led. I manually found the best frequency ...
38 views

Energy transfer between oscillators [closed]

Suppose I have two mechanical oscillators $a(t), b(t)$, coupled through the interaction $V_\text{int} = \mu^2 a(t) b(t)$. Is there a simple way to express the rate of energy transfer from $a$ to $b$ ...
60 views

Why does Joule's Law of Heating defined by $H=i^2R$ only? [duplicate]

Joule's Law Of Heating states that for a conductor Heat loss is given by $$H=i^2Rt$$ Couldn't we substitute $$V=iR$$ and show that $H=(V^2/R)t$ ? If this is so, when transmitting power across large ...
101 views

Power in a wind turbine

An wind turbine starts turning by a wind speed of $v_b$ and it stops turning (rated wind speed, to prevent overloading) by a wind speed of $v_g$. By wind speeds between $v_b<v<v_g$, the power ...
54 views

Why does an alternator slow down when the 3 phases are shorted?

I'm designing a small wind turbine and noticed that when i short the three wires coming out of the alternator, the alternator is breaking and the blade RPM is dropping. What is the explanation for ...