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A physical system of electromechanical energy conversion consists of a stationary part creating a magnetic field with electric energy input, and a moving part giving mechanical energy output. If the movable part is kept fixed, the entire electrical energy input will be _______
A) stored in the magnetic field
B) stored in the electric field
C) divided equally between the magnetic and electric fields
D) zero
stored in the magnetic field
In an electromechanical energy conversion system, the total electrical energy input is converted into mechanical output, stored field energy, and energy losses. When the moving part is held fixed, the mechanical output is zero because the differential mechanical work done dWmechтАЛ=FfldтАЛтЛЕdx=0 (since dx=0). Neglecting losses, all the electrical energy supplied to the stationary winding is stored as magnetic field energy.
In an electromechanical energy conversion system, the total electrical energy input is converted into mechanical output, stored field energy, and energy losses. When the moving part is held fixed, the mechanical output is zero because the differential mechanical work done dWmechтАЛ=FfldтАЛтЛЕdx=0 (since dx=0). Neglecting losses, all the electrical energy supplied to the stationary winding is stored as magnetic field energy.
dWelecтАЛ=dWfldтАЛ+dWmechтАЛ тАФ Energy balance equation (lossless system)
dWmechтАЛ=FfldтАЛтЛЕdx тАФ Differential mechanical work done
WfldтАЛ=тИлid╬╗=21тАЛLi2 тАФ Stored magnetic field energy in a linear system
According to the law of conservation of energy for a magnetic field system, dWelecтАЛ=dWfldтАЛ+dWmechтАЛ. Holding the rotor/movable part stationary sets dx=0, rendering dWmechтАЛ=0. Consequently, dWelecтАЛ=dWfldтАЛ, meaning the entire input electrical energy goes into changing and storing energy in the magnetic field.
Magnetic field acts as the coupling medium between electrical and mechanical domains in electromagnetic devices.
If mechanical displacement dx=0, no mechanical work is performed by or on the system (dWmechтАЛ=0).
In inductive devices (such as coils and transformers), input electric power converts directly into stored magnetic field energy WfldтАЛ.
Standard inductive magnetic circuits store energy predominantly in the magnetic field, while electrostatic/capacitive systems store energy in the electric field.
Option B is incorrect because magnetic coupling devices utilize magnetic field energy, not electrostatic field energy.
Option C is incorrect because energy is not divided into electric fields for purely inductive electromagnetic systems.
Option D is incorrect because electrical energy continues to flow into the system until the magnetic field reaches steady-state saturation.
A is correct тАФ Since the movable part is fixed, the mechanical work output is zero, causing all net input electrical energy to be stored in the magnetic field.
Always identify the energy coupling medium (magnetic vs. electric field) and check if displacement dx=0 or flux ╬╗ is constant to quickly eliminate mechanical work or field change terms.