ELECTRICAL ENCYCLOPEDIA

Voltmeter http://en.wikipedia.org   A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter. Voltmeters are made in a wide range of styles. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant. Voltmeter Design http://hyperphysics.phy-astr.gsu.edu/   A voltmeter is placed in parallel with a circuit element to measure the volta

Mutual Inductance and Coupled Inductors http://hyperphysics.phy-astr.gsu.edu   When an emf is produced in a coil because of the change in current in a coupled coil , the effect is called mutual inductance. The emf is described by Faraday's law and it's direction is always opposed the change in the magnetic field produced in it by the coupled coil (Lenz's law ). The induced emf in coil 1 is due to self inductance L. Mutual Inductance and Basic Operation http://www.allaboutcircuits.com   As an inductor, we would expect this iron-core coil to oppose the applied voltage with its inductive reactance, limiting current through the coil as predicted by the equations XL = 2πfL and I=E/X (or I=E/Z). For the purposes of this example, though, we need to take a more detailed look at the interactions of voltage, current, and magnetic flux in the device. Inductance and Magnetic Energy http://web.mit.edu   The first coil has N1 turns and carries a current I1 which gives rise to a magnet