Current is produced by the movement of charge carriers within a material. Typically we think of negatively charged electrons as charge carriers. However, depending on the material, the charge carriers could also be positively charged holes or ions, or a mixture of different kinds of charge carriers. If a magnetic field (B) is applied perpendicular to the direction of the current (I), the charge carriers will experience a force known as the Lorentz force (FL) (see What is a Homopolar Motor?)....

Magnetic resonance imaging (MRI) is a powerful imaging technique used to investigate the body. MRI scanners use very strong magnetic fields and radio waves, which interact with protons in tissues to create a signal that is then processed to form images of the body. The protons (hydrogen atoms) can be thought of as tiny bar magnets, with a north pole and a south pole, spinning on an axis – like a planet. Normally, the protons are randomly aligned, but when a strong magnetic field is applied, the...

Eddy currents are currents which circulate in conductors like swirling eddies in a stream. They are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field. They can be created when a conductor is moving through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying i.e. anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field can produce eddy...

Wearable devices, such as health monitors and sensors, are of great interest. One of the major limitations in making these devices a practical reality has been the power supply – the need for large, heavy batteries. Movement generates power and a human can produce 10s of Watts just from walking and up to a kilowatt when sprinting. Harvesting this energy has the potential to overcome the power supply problem and German researchers have recently built power harvesting devices which are small...

A ferrofluid is a liquid which becomes highly magnetized in the presence of a magnetic field. The distinctive ‘spikey’ shape of a magnetized ferrofluid is caused by the need to find the most stable shape in order to minimize the total energy of the system, an effect known as the normal-field instability. The fluid is more easily magnetized than the surrounding air, so is drawn out along the magnetic field lines, resulting in the formation of peaks and troughs. However, the extension of the...