# How It Works: Science and Technology - Vol. 8

By Wendy Horobin | Go to book overview

Induction

An electromagnetic
field is generated in a
Loop of wire when it
moves through a region
of changing magnetic
field. Mutual inductance
occurs in a loop near to
a changing electric
current. Self-inductance
is generated within the
circuit itself against
the battery's current.

The word inductance comes from induce, meaning [to bring about] or [to give rise to.] In electromagnetism, it refers to the ability of a changing current to give rise to a voltage.

In an electrical circuit, currents arise in conductors that connect points of different electrical potential, or voltage. The voltage is generally established by a device that converts another form of energy into electrical energy. A battery, for example, converts chemical energy into electrical energy; a solar cell converts light energy into electrical energy; and a generator converts motional energy into electrical energy by forcing a conductor to move through a magnetic field.

The moving charges that constitute an electric current set up a magnetic field in the space around them. As long as the field is unchanging it will have no effect on a second, nonmoving conductor placed in it. If, however, the second conductor is moving or the magnetic field around it is changing, a voltage is induced in it, and if it is part of a complete circuit, a current will flow in response. The magnitude of the induced electromotive force will be proportional to the rate at which the magnetic flux (field strength x area measured perpendicular to the field direction) is changing.

Inductance and changing current

Potential differences give rise to currents, which in turn create magnetic fields. Any change in the current will create a change in the field, which induces a voltage in any neighboring circuits and in the original circuit as well.

The induction of a voltage in one circuit by the changing current in another is termed mutual inductance. The additional voltage induced in a circuit by changes in its own magnetic field is termed self-inductance. According to a principle known as Lenz's law, the voltage induced in any circuit by a changing magnetic flux will produce currents that resist the change in flux. Selfinductance is therefore a factor that resists any change in current.

Because the magnitude of induced voltage is proportional to the rate of change of current, high-frequency (fast-changing) current signals will produce larger induced voltages than lowfrequency (slow-changing) signals. Furthermore, as these induced voltages always try to impede the current that produced them, they will impede higher frequencies more than lower frequencies. Steady currents are not affected by inductance.

In many situations self-inductance can be a nuisance. For example, when transmitting a signal

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How It Works: Science and Technology - Vol. 8
Table of contents

#### Table of contents

• Title Page *
• Contents *
• Gold 1013
• Governor 1017
• Grass-Cutting Equipment 1018
• Gravity 1020
• Gun 1023
• Gyrocompass 1028
• Gyroscope 1030
• Hair Treatment 1032
• Halogen 1034
• Hang Glider 1037
• Head-Up Display 1039
• Hearing 1041
• Heart 1045
• Heart Pacemaker 1048
• Heart Surgery 1049
• Heat Engine 1053
• Heat Exchanger 1054
• Heating and Ventilation Systems 1056
• Heat Pump 1063
• Helicopter 1065
• Hi-Fi Systems 1071
• High-Speed Photography 1077
• Holography 1080
• Hormone 1084
• Horticulture 1088
• Hosiery and Knitwear Manufacture 1090
• Hurricane and Tornado 1094
• Hydraulics 1100
• Hydrocarbon 1105
• Hydrodynamics 1109
• Hydroelectric Power 1112
• Hydrofoil 1116
• Hydrogen 1118
• Hydroponics 1120
• Hygrometer 1123
• Ignition System, Automobile 1124
• Image Intensifier 1128
• Immunology 1132
• Induction 1138
• Inertia 1142
• Information Technology 1147
• Ink 1151
• Index i
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