# Tag Info

## Hot answers tagged power

3

$11 W$ means the bulb uses 11 watts of power when it's operating at the rated voltage. If you run it for an hour for example, it will cost $0.011 kWh$, and your power company will bill you for ___ (check your local electricity prices). You can also calculate how much current the bulb will draw since you know the voltage, as well as the resistance of the bulb ...

2

This is a great opportunity to teach your students about performing an energy balance, about various heat transfer modes, about solving differential equations (or approximating them with finite-difference equations), and about model simplification. For any small section of the wire (length $dx$, cross-sectional area $A$), we can perform an energy balance ...

2

Yes, the current depends on the internal resistance. And that resistance has been adjusted to give a current that corresponds to 11 W. (By the way, note that we typically don't symbolise the wattage, the power, with $W$ but rather with $P$.)

1

The fission is happening everywhere there is salt with fuel in it. Most of the fissions are occurring in the "main" part of the core, where the geometry is favorable for neutron multiplication, but there are fissions occurring everywhere in the primary loop. This is one of the challenges of molten salt reactors. In addition to the prompt neutrons, ...

1

$11\rm\,W$ means that at its working voltage, on average over a period electrical energy is converted into other forms of energy, heat and light, at a rate of $11\rm\,J/s$. One has to be careful when quoting the resistance of a light bulb as a bulb's resistance depends on the applied voltage with a higher applied voltage increasing the temperature of the ...

1

You will have done work. Mathematically, $W = F \cdot dS$. Since that "particular point" moved, there is a nonzero displacement in the direction of the force, and work is done.

1

The Energy given by the motor between point 1 and point 2 would be equal to the difference in Energy between point 1 and 2. In the second part as you have been given Power of motor, you can use P=dE/dt to determine the time taken. For third and fourth part you simply have to conserve energy as the motor is only between point 1 and 2.

1

You are right, the flow of electricity (specifically: voltage x current) performs work in electric motors, as used in appliances and whatnot. Let me try to clear up your confusions: Let us imagine an electric motor, with a certain internal resistance R. We connect it to a battery of voltage V but instead of letting the motor shaft turn, we lock it so ...

1

Is this the sort of thing you're looking for? If the power is applied from time $t=0$, when the object is at rest, then at time $t$, $$\frac12 m v^2 =Pt.$$ Writing $v=\frac{ds}{dt}$, separating variables and preparing to integrate, $$\int_0^{s_1} ds =\int_0^{t_1} \sqrt{\frac{2Pt}{m}} dt$$ So $$s_1=\frac23 \sqrt{\frac{2P}{m}} t_1^{\ 3/2}$$ We can now drop the ...

1

When you pass a current through a wire, for a fraction of a second (a time $\Delta t$, say) almost all the electrical work ($I^2 R\Delta t$) goes into internal thermal energy in the wire (that is, as you say, $mc\Delta T$). But as the wire gets hotter more and more of the energy being supplied is lost as heat to the surroundings. Let's suppose that the wire ...

1

The thing is, when I then try some simple model like using specific heat (I used the old thing from first year chemistry $Q = mc\Delta > T$)I get rather large numbers for temperature increase, on the order of thousands of degrees for a 120 V circuit. That is the correct equation for calculating the energy delivered to the wire, but it doesn't take into ...

1

This is a question about anthropogenic heat flux aka waste heat relative to anthropogenic global warming. According to Mark Flanner "Integrating anthropogenic heat flux with global climate models" 2009 - Although AHF exceeds 100 W m−2 in urban centers [Oke, 1988; Ichinose et al., 1999] and is treated in some urban- and meso-scale models [e.g., ...

Only top voted, non community-wiki answers of a minimum length are eligible