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Collisions of these electrons with the atoms of the sheet exert a drag force on the sheet. Eddy current brake. The North magnetic pole piece (top) in this drawing is shown further away from the disk than the South; this is just to leave room to show the currents. In an actual eddy current brake the pole pieces are positioned as close to the ...
a is the distance between the two plates; The force is negative, indicating that the force is attractive: by moving the two plates closer together, the energy is lowered. The presence of ħ shows that the Casimir force per unit area F c / A is very small, and that furthermore, the force is inherently of quantum-mechanical origin.
In the Ampèrian loop model, there is also a force on a magnetic dipole due to a non-uniform magnetic field, but this is due to Lorentz forces on the current loop that makes up the magnetic dipole. The force obtained in the case of a current loop model is = (), where the gradient ∇ is the change of the quantity m · B per unit distance, and ...
In electromagnetism, displacement current density is the quantity ∂D/∂t appearing in Maxwell's equations that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual
When an electron leaves a helium atom, it leaves an electron hole in its place. This causes the helium atom to become positively charged. In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle denoting the lack of an electron at a position where one could exist in an atom or atomic lattice.
For electrons, the current density J (amperes per meter squared) is written: = = /. where is the anode current and S the surface area of the anode receiving the current; is the magnitude of the charge of the electron and is its mass. The equation is also known as the "three-halves-power law" or the Child–Langmuir law.
A parallel plate capacitor. Using an imaginary box, it is possible to use Gauss's law to explain the relationship between electric displacement and free charge. Consider an infinite parallel plate capacitor where the space between the plates is empty or contains a neutral, insulating medium. In both cases, the free charges are only on the metal ...
Now the field is turned back on, and the electric force on the drop is =, where q is the charge on the oil drop and E is the electric field between the plates. For parallel plates =, where V is the potential difference and d is the distance between the plates.