Show Advanced Search


Containing Text
- - -
Filter by author or institution
Filter by publication date
October, 2006
Filter by journal section

Filter by science education

Magnetic Fields: Areas of attractive or repulsive force surrounding Magnets.

Magnetic Fields

JoVE 10384

Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN

Magnetic fields can be generated by moving charges, such as an electrical current. The magnetic field generated by a current can be calculated from the Maxwell equation. In addition, magnetic objects such as bar magnets can also generate magnetic fields due to microscopic dynamics of charges inside the material. Magnetic fields will exert magnetic force on other moving charges or magnetic objects, with the force proportional to the magnetic field. Magnetic fields are fundamental to electromagnetism and underlie many practical applications ranging from compasses to magnetic resonance imaging. This experiment will demonstrate magnetic fields produced by a permanent bar magnet as well as an electrical current, using small compass needle magnets that align with magnetic fields. This experiment will also demonstrate the force exerted by the magnetic fields produced by a current on another current-carrying wire.

 Physics II

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

1Institute of Nuclear and Physical Engineering, Slovak University of Technology in Bratislava, Slovakia, 2Department of Nuclear Reactors, Czech Technical University in Prague, Czech Republic, 3Department of Experimental Physics, Palacky University Olomouc, Czech Republic, 4Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia, 5Institute of Laboratory Research on Geomaterials, Faculty of Natural Sciences, Comenius University in Bratislava, Slovakia

JoVE 57657


Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

1Institute of Imaging Science, Vanderbilt University, 2Department of Radiology and Radiological Sciences, Vanderbilt University, 3Department of Biomedical Engineering, Vanderbilt University, 4Department of Molecular Physiology and Biophysics, Vanderbilt University, 5Department of Physical Medicine and Rehabilitation, Vanderbilt University, 6Department of Physics and Astronomy, Vanderbilt University

JoVE 52352


Electric Charge in a Magnetic Field

JoVE 10133

Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA

This experiment duplicates J.J. Thomson's famous experiment at the end of the 19th century, in which he measured the charge-to-mass ratio of the electron. In combination with Robert A. Millikan's oil-drop experiment a few years later that produced a value for the charge of the electron, the experiments enabled scientists to find, for the first time, both the mass and the charge of the electron, which are key parameters for the electron. Thomson was not able to measure the electron charge or the electron mass separately, but he was able to find their ratio. The same is true for this demonstration; although here there is the advantage of being able to look up the values for the magnitude of the charge on the electron(e) and the mass of the electron (me), which are now both known precisely.

 Physics II

AC Synchronous Machine Characterization

JoVE 10168

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

Three-phase wound-rotor synchronous motors are less popular than permanent magnet rotor synchronous motors due to the brushes required for the rotor field. Synchronous generators are much more common and available in most existing power plants, as they have excellent frequency and voltage regulation. Synchronous motors have the advantage of almost 0% speed regulation due to the fact that the rotor speed is exactly the same as the stator's magnetic field speed, causing the rotor speed to be constant, irrespective of how much the motor's shaft is loaded. Thus, they are very suitable for fixed speed applications. The objectives of this experiment are to understand the concepts of starting a three-phase synchronous motor, V-curves for various loads where the load affects the motor power factor, and the effect of loads on the angle between the terminal voltage and back e.m.f.

 Electrical Engineering

Cell Labeling and Targeting with Superparamagnetic Iron Oxide Nanoparticles

1Division of Cardiovascular Diseases, Mayo Clinic, 2Division of Engineering, Mayo Clinic, 3School of Medicine, Pharmacy and Health, Durham University, 4Regional Center for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, 5Mayo Clinic College of Medicine, Mayo Clinic

JoVE 53099


DC Motors

JoVE 10166

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

The DC machine operates with DC currents and voltages as opposed to an AC machine, which requires AC currents and voltages. DC machines were the first to be invented and utilize two magnetic fields that are controlled by DC currents. The same machine can be easily reconfigured to be a motor or generator if appropriate field excitation is available, since the DC machine has two fields termed field and armature. The field is usually on the stator side and the armature is on the rotor side (opposite or inside-out compared to AC machines). Field excitation can be provided by permanent magnets or a winding (coil). When current is applied to the armature or rotor coil, it passes from the DC source to the coil through brushes that are stationary and slip rings mounted on the rotating rotor touching the brushes. When the rotor armature coil is a current-carrying loop, and is exposed to an external field from the stator or field magnet, a force is exerted on the loop. Since the loop is "hanging" on both sides of the motor using bearings, the force produces a torque that will rotate the rotor's shaft rather than move it in any other direction. This rotation causes the magnetic fields to align but at the same time

 Electrical Engineering

Interictal High Frequency Oscillations Detected with Simultaneous Magnetoencephalography and Electroencephalography as Biomarker of Pediatric Epilepsy

1Fetal-Neonatal Neuroimaging and Developmental Science Center, Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Harvard Medical School, 2Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, 3Division of Epilepsy Surgery, Department of Neurosurgery, Boston Children's Hospital, Harvard Medical School, 4Division of Epilepsy and Clinical Neurophysiology, Department of Neurology, Boston Children's Hospital, Harvard Medical School

JoVE 54883


The Evans Method

JoVE 10304

Source: Tamara M. Powers, Department of Chemistry, Texas A&M University 

While most organic molecules are diamagnetic, wherein all their electrons are paired up in bonds, many transition metal complexes are paramagnetic, which has ground states with unpaired electrons. Recall Hund's rule, which states that for orbitals of similar energies, electrons will fill the orbitals to maximize the number of unpaired electrons before pairing up. Transition metals have partially populated d-orbitals whose energies are perturbed to varying extents by coordination of ligands to the metal. Thus, the d-orbitals are similar in energy to one another, but are not all degenerate. This allows for complexes to be diamagnetic, with all electrons paired up, or paramagnetic, with unpaired electrons. Knowing the number of unpaired electrons in a metal complex can provide clues into the oxidation-state and geometry of the metal complex, as well as into the ligand field (crystal field) strength of the ligands. These properties greatly impact the spectroscopy and reactivity of transition metal complexes, and so are important to understand. One way to count the number of unpaired electrons is to measure the magnetic susceptibility, χ, of the coordinatio

 Inorganic Chemistry

AC Induction Motor Characterization

JoVE 10150

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

The objectives of this experiment are to find the equivalent circuit parameters of a three-phase induction motor using the per-phase equivalent circuit and tests similar to those used in transformer characterization. In electrical engineering, an equivalent circuit (or theoretical circuit) can be determined for a given system. The equivalent circuit retains all characteristics of the original system, and is used as a model to simplify calculations. Another objective is to operate the motor in the linear torque-speed region.

 Electrical Engineering

Recording Brain Electromagnetic Activity During the Administration of the Gaseous Anesthetic Agents Xenon and Nitrous Oxide in Healthy Volunteers

1Centre for Human Psychopharmacology, Swinburne University of Technology, 2Department of Anaesthesia and Pain Management, St. Vincent's Hospital Melbourne, 3Brain and Psychological Science Research Centre, Swinburne University of Technology, 4Department of Anaesthesiology, University of Auckland

JoVE 56881


AC Synchronous Machine Synchronization

JoVE 10167

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

Three-phase wound-rotor synchronous generators are the main source of electrical power worldwide. They require a prime mover and an exciter in order to generate power. The prime mover can be a turbine spun by fluid (gas or liquid), thus the sources of the fluid can be water running off a dam through a long nozzle, steam from water evaporated using burned coal, etc. Most power plants including coal, nuclear, natural gas, fuel oil, and others utilize synchronous generators. The objective of this experiment is to understand the concepts of adjusting the voltage and frequency outputs of a three-phase synchronous generator, followed by synchronizing it with the grid. The effects of field current and speed variations on the generator output power are also demonstrated.

 Electrical Engineering

The Use of Magnetic Resonance Spectroscopy as a Tool for the Measurement of Bi-hemispheric Transcranial Electric Stimulation Effects on Primary Motor Cortex Metabolism

1Department of Psychology, University of Montréal, 2Montreal Neurological Institute, McGill University, 3Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota

JoVE 51631


Fabrication of a Functionalized Magnetic Bacterial Nanocellulose with Iron Oxide Nanoparticles

1Department of Bioengineering, University of Illinois at Urbana-Champaign, 2Department of Nuclear, Plasma and Radiological Engineering, University of Illinois at Urbana-Champaign, 3Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, 4Program of Study and Control of Tropical Diseases (PECET), University of Antioquia, 5Sealy Center for Vaccine Development, University of Texas Medical Branch, 6WHO Collaborating Center for Vaccine Research, Evaluation and Training on Emerging Infectious Diseases, University of Texas Medical Branch, 7Beckman Institute, University of Illinois at Urbana-Champaign

JoVE 52951


More Results...