Terminology And Units For Magnetic Circuit

Question 1

Define Magnetic circuit

Answer 1

A term that refers to the path along which the flux lines follow as they form a complete loop

Question 2

Define the basic law for magnetic circuits

Answer 2

A magnetic flux in a circuit is directly proportional to the magnetomotive force (MMF) and inversely proportional to the reluctance of the magnetic circuit.

Question 3

When a coil of wire has DC current flowing, it creates?

Answer 3

Millions of flux lines
1Weber (Wb) = 10^8 flux lines

Question 4

The number of weber created by a coil is indicated by two factors.

Answer 4

1- The STRENGTH of the magnetomotive force (Fm or MMF). The value of flux is directly proportional to MMF

2- the RELUCTANCE (Rm) of the material around the coil. The value of flux is inversely proportional to the RELUCTANCE.

Question 5

Define reluctance

Answer 5

The opposition to the setting up of magnetic lines of flux.

Question 6

Define air gap

Answer 6

Air space or equivalent filler of non-magnetic material in the core (between the pole) of an electromagnetic coil assembly.

Question 7

Define alloy

Answer 7

Combination of two or more elements (usually metallic) used in the manufacture of permanent magnet.

Alnico is a common alloy consisting of iron, aluminium, nickel and cobalt.

Question 8

Define BH Curve

Answer 8

A graph which demonstrates the relationship between flux density (B) and magnetizing force (H) for an electromagnet of specific core material.

Question 9

Define electromagnet

Answer 9

A temporary magnet constructed of a core and coil assembly which produces magnetic flux only while an electrical current flows through the coil.

Question 10

Define ferromagnetic

Answer 10

Used to describe a material that has magnetic properties similar to iron.

Question 11

Define flux density

Answer 11

Is the quantity of magnetic flux lines per unit area.

Unit: Tesla

Question 12

Define Hysteresis

Answer 12

The tendency of a magnetic flux to lag behind the magnetizing force that is producing it.

Normally depicted in a graphical form called hysteresis loop.

Question 13

Define Magnetic flux

Answer 13

The invisible lines of force that exist within any magnetic circuit.

Question 14

Define Magnetic screen ( Shield)

Answer 14

A substance that is used to divert magnetic lines by providing an easier path for them to pass through.

Question 15

Define magnetizing force

Answer 15

The magnetomotive force applied per unit length of a magnetic circuit.

Symbol: H
Units: Amp-turns per metre

Question 16

Define permeability

Answer 16

A measure of the ease with which the magnetic flux can be established within a material.

Found by taking the ratio ‘B/H’

Comparable to conductivity in electrical circuit

Question 17

Define reluctance

Answer 17

The opposition that a material offers to the establishment of magnetic flux.

This is the equivalence of resistance in an electrical circuit

Symbolism: ‘S’
Unit: amper-turn per Weber

Question 18

Define residual magnetism

Answer 18

The permanent magnetism retained by a material after the magnetizing force has been removed.

Question 19

Define saturation

Answer 19

A condition where any further increased in magnetizing force does not produce any appreciable increase in magnetic flux density for an electromagnet.