positive feedback

Examples of positive feedback in the following topics:

• Mechanical Work and Electrical Energy

  • If the induced EMF were in the same direction as the change in flux, there would be a positive feedback causing the rod to fly away from the slightest perturbation.

• Faraday's Law of Induction and Lenz' Law

  • In fact, if the induced EMF were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated.

• Convection

  • Such a mechanism is called positive feedback, since the process reinforces and accelerates itself.
  • The rise of clouds is driven by a positive feedback mechanism.

• Inductance

  • From Lenz's law, a changing electric current through a circuit that has inductance induces a proportional voltage which opposes the change in current (if this wasn't true one can easily see how energy could not be conserved, with a changing current reinforcing the change in a positive feedback loop).

• Lasers

  • A laser consists of a gain medium, a mechanism to supply energy to it, and something to provide optical feedback.
  • A laser consists of a gain medium, a mechanism to supply energy to it, and something to provide optical feedback (usually an optical cavity).
  • The most common type of laser uses feedback from an optical cavity--a pair of highly reflective mirrors on either end of the gain medium.

• Geomagnetism

  • Near the surface of Earth, its magnetic field can be closely approximated by the field of a magnetic dipole positioned at the center of Earth and tilted at an angle of about 10° with respect to the rotational axis of Earth .
  • A magnetic field is generated by a feedback loop: Current loops generate magnetic fields (Ampère's law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force).

• The Thomson Model

  • Thomson proposed that the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges.
  • Stoney had proposed that atoms of electricity be called electrons in 1894) surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding" .
  • The electrons (as we know them today) were thought to be positioned throughout the atom in rotating rings.
  • In this model the atom was also sometimes described to have a "cloud" of positive charge.
  • Now, at least part of the atom was to be composed of Thomson's particulate negative corpuscles, although the rest of the positively charged part of the atom remained somewhat nebulous and ill-defined.

• Graphical Interpretation

  • is a graph of an object's position over time.
  • In the beginning, the object's position changes slowly as it gains speed.
  • In the middle, the speed is constant and the position changes at a constant rate.
  • As it slows down toward the end, the position changes more slowly.
  • Its position then changes more slowly as it slows down at the end of the journey.

• Stress and Strain

  • If the charge is positive, field lines point radially away from it; if the charge is negative, field lines point radially towards it.
  • This charge is either positive or negative.
  • If the charge is positive, as shown above, the electric field will be pointing in a positive radial direction from the charge q (away from the charge) and the following text explains why.
  • The electric field of a positively charged particle points radially away from the charge.
  • The positive r direction points away from the origin, and the negative r direction points toward the origin.

• Electric Field from a Point Charge

  • If the charge is positive, field lines point radially away from it; if the charge is negative, field lines point radially towards it .
  • This charge is either positive or negative.
  • If the charge is positive, as shown above, the electric field will be pointing in a positive radial direction from the charge q (away from the charge).
  • The electric field of a positively charged particle points radially away from the charge.
  • The positive r direction points away from the origin, and the negative r direction points toward the origin.