Magnetic field
Introduction
A Magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field.
Fundamental concepts
Magnetic field lines
Magnetic field lines are a visual tool used to represent magnetic fields. They describe the direction of the magnetic force on a north monopole at any given position. Because monopoles are not found to exist in nature, we also discuss magnetic field lines in terms of lines formed in ferro-magnetic material by a magnet. The field lines are the paths that a north magnetic monopole would seek to travel.
Magnetic flux
Magnetic flux is the product of the average magnetic field times the perpendicular area that it penetrates. It is usually measured with a fluxmeter, which contains measuring coils and electronics, that evaluates the change of voltage in the measuring coils to calculate the measurement of magnetic flux.
Magnetic moment
The magnetic moment of a magnet is a quantity that determines the force that the magnet can exert on electric currents and the torque that a magnetic field will exert on it. A loop of electric current, a bar magnet, an electron, a molecule, and a planet all have magnetic moments.
Magnetic field and magnetic forces
Magnetic fields are extremely useful. The magnetic field of the Earth shields us from harmful radiation from the Sun, magnetic fields allow us to diagnose medical problems using an MRI, and magnetic fields are a key component in technologies like recording tapes and hard drives.
Magnetic field of the Earth
The Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field of the Earth is of great importance in navigation, as it is used in compasses.
Magnetic fields in medicine
Magnetic fields play a key role in medicine, particularly in imaging. Magnetic Resonance Imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body.
Magnetic fields in technology
Magnetic fields are also used in various technologies such as magnetic recording and data storage. In a hard disk drive, a thin layer of magnetic material is deposited on a high precision disk. Data is stored, retrieved and erased using magnetic fields created by very tiny electromagnets.
Measurement and units
Magnetic fields are measured in units of tesla (T). The tesla is equivalent to the newton per ampere-meter (N/A⋅m). In the CGS system, which is also still used, the unit of magnetic field is the gauss (G). One tesla equals 10,000 gauss.