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### PHYSICS DICTIONARY

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Macroscopic

Large enough to be perceived or examined by naked eye.

(or)

Anything which is considered for bulk of matter as a whole.

Magnetic Dipole

An object such as current loop, an atom or a bar magnet, that experiences torques due to magnetic forces.

Magnetic Field Intensity

It is measured by force acting on unit magnetic pole. The field intensity is also specified by number of lines of force intersecting unit area normal to the field, equal numerically to field strength in Oersted.

Magnetic Induction

When any substance is subjected to a magnetic field, the magnetic flux per unit area taken perpendicular to direction of the flux is called magnetic induction.

Magnetic Permeability

Property of materials modifying the action of magnetic poles placed there in and modifying the magnetic induction resulting when the material is subjected to a magnetic field or magnetizing force. The permeability may be defined as ratio of magnetic induction in the substance to magnetizing field to which it is subjected.

Magic Number

When the number of protons is 2,8,20,28,50,82 or the no. of neutrons is 2,8,20,28,50,82,126 the nucleus is observed particularly stable and these numbers are referred to as magic numbers. Nuclei in which the no. of protons as well as no. of neutrons is equal to magic number belong to most stable group of nuclei.

Magnetic Dipole

Small bar magnet composed of north and south poles.

Magnetic Flux Density

Also called as magnetic induction represents magnitude of internal field strength with in a substance that is subjected to an external magnetic field.

Magnetic Moment

A vector quantity that is a measure of the torque exerted on a magnetic system when placed in magnetic field and that for a magnet is the product of distance between its poles and the strength of either pole. It is usually created by electric current flowing in wire or with orbital motion of spinning electron caused intrinsic magnetic moment.

Magnetic Potential

Magnetic potential at a point is measured by the work required to bring unit positive pole from an infinite distance (zero potential) to the point.

Magnetic Resonance Imaging (MRI)

The use of magnetic fields and radio waves (instead of the X-rays employed in the CT scan) to visualize body structures and how they function. The powerful magnet, large enough to enclose the body, forces the atomic nuclei in most material such as soft tissue to align themselves with the magnetic field. Radio waves are aimed at the selected area to excite the atoms which, when the waves are stopped, emit signals that are converted to computer-generated pictures.

Magnetic Susceptibility

It is a dimension less quantity and is proportionality constant between magnetization & applied external magnetic field.

Magnetism

Old study which deals with simplest sources of magnetic fields, the permanent (bar) magnets. Magnets and magnetic fields are dealt without considering electrical charges in motion.

Magnetization

The phenomenon of formation of magnetic dipoles inside material due to application of uniform magnetic field.

(or)

The total magnetic moment per unit volume of material is called as magnetization.

Magnetoresistance

It is property of crystal to change its electrical resistance when a magnetic field is imposed on it.

Magnetometer

An instrument used for measuring the intensity or direction of a magnetic field, especially the earth’s magnetic field.

Magnetostriction

The phenomenon of change in shape and density of a substance, especially a ferromagnetic substance, when exposed to a magnetic field is called magnetostriction.

Magnification

The apparent enlargement of an object by an optical instrument is called magnification.