Hi, Physics equation help!

[chaser0]

I am quite confused on the idea of the power equation

I know that Power=Work/time
But I have written here that
Power= Work/Efficiency


Are these two equations the same?
I thought that maybe the second equation was actually the mechanical efficiency equation and I just mislabeled it~
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Another question:

Do constructive and destructive interference ONLY refer to when the waves are completely out of or in synch?
The examples for the beat frequency make it seem like the waves feel additive/destructive effects regardless of "synchiness"

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Also, the Resonance Frequency of a material is only one certain frequency?
This is confusing as jelly vibrates more vigorously regardless of the frequency of vibration you put into it...

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[venacontracta]

Power is the rate at which work is done (for mechanical power) or energy is transferred (for electrical power).

Mechanical:
Power = work / time
Electrical:
P = VI

Efficiency for a machine is the ratio between the rate at which useful work is done by the machine and the rate at which the machine consumes energy.

In other words, if an engine burns 3000 Joules worth of gasoline per second and does 1500 Joules worth of useful work in a second, its efficiency is 0.5. The energy which is not converted to useful work is lost as heat.

The equation you have linking efficiency and power is incorrect. Efficiency is a ratio, and both the top and bottom terms are energy per unit time (power).

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No, you can have partially constructive or partially destructive interference.

When two waves are perfectly in sync, you have totally constructive interference. When they are "totally out of sync" (180 degrees out of phase), you have totally destructive interference. For anything in between there, ask yourself whether the result of the interference is to make the sum of the two waves' amplitudes higher or lower, and that will tell you whether you have partially constructive or partially destructive interference.

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A mechanical system has multiple frequencies at which resonance occur. Think of resonance as "the existence of a standing wave." You have formulas for the possible wavelengths of standing waves in a given system (the formulas for harmonics). The frequencies of these harmonics are the resonant frequencies of the system.

You are overdoing the concept of resonant frequencies. All it means is that when you drive a system at the resonant frequency, amplitude of the resulting wave is maximized. It doesn't mean using any other frequency does nothing. A system consisting of jello will jiggle the most it can ever jiggle when you shake it at its resonant frequency, but that doesn't mean it won't jiggle at all when you shake it at any other frequency.

 

[chaser0]

Thank you so much!



Another question however, this one is about Dipoles


I know that Dipoles have a net force of Zero (only if the Electric field force is equal on either side), Does this also mean that zero work is being done even though the dipole is spinning?? Strange how something can continually spin yet do zero work...



Also, why is the electrical Force equation different from the Electric Dipole moment equation??
I would think they would be the same as they both include the same kind of charges.
(Perhaps electric Dipole moment is not a force? If that is so, could the same charges used for the Electric field equation be applied to an electric dipole equation??)

 

[venacontracta]

If you put a dipole in a electric field (electric dipole in electric field or magnetic dipole in magnetic field) it doesn't constantly spin, it orients itself in the manner which minimizes potential energy and just stays there. To find the amount of work done by the field in doing this, find the change in potential energy between where the dipole started and where it ended up. See these two links for details for electric and magnetic situations:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dipole.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magpot.html

Dipole moments are not forces. They are measures of polarity - quantitative measurements of the separation of charge.

Thank you so much!



Another question however, this one is about Dipoles


I know that Dipoles have a net force of Zero (only if the Electric field force is equal on either side), Does this also mean that zero work is being done even though the dipole is spinning?? Strange how something can continually spin yet do zero work...



Also, why is the electrical Force equation different from the Electric Dipole moment equation??
I would think they would be the same as they both include the same kind of charges.
(Perhaps electric Dipole moment is not a force? If that is so, could the same charges used for the Electric field equation be applied to an electric dipole equation??)