Notes 3.1.3 - Magnetic Fields

Sep 20, 2026

Uploaded by James

Study notes on magnetic fields and electromagnetism, covering magnetite and lodestone, magnetic poles, and ferromagnetism at the atomic and domain level. Explains why unmagnetised iron has randomly oriented domains and how an external magnetic field aligns them. Defines magnetic fields, introduces magnetic field lines with key drawing rules and the Tesla unit. Describes magnetic forces using vector nature, plus electromagnetism via Oersted’s discovery and direction dependence on current. Includes diagram conventions and right-hand hand rules (grip, slap, solenoid) with an applied example predicting wire motion.

LanguageEnglish

CategoryExam

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Section 3.1.3 – Magnetic Fields

Magnetic Fields

Magnetic Forces

Electromagnetism

Diagrammatic Notation

Electromagnetic “Hand Rules”

Example 1

Notes 3.1.3 Page 1 Section 3.1.3 – Magnetic Fields Magnetic Fields The iron ore called magnetite (an oxide of iron) is part of a naturally occurring rock that the Anglo-Saxons called lodestone (direction stone) . It was used by early navigators as a compass. A suspended magnet will turn so that one end will point towards the north pole of the Earth and the other towards the south pole. Accordingly they are called: 􀁸 North seeking pole (North pole) 􀁸 South seeking pole (South pole) Iron (Fe), nickel (Ni), cobalt (Co) and some of the rare earths (gadolinium, dysprosium) exhibit a unique magnetic behavior which is called ferromagnetism. The magnetic phenomenon, which originates at the atomic level, causes unpaired electron spins to line up parallel with each other in a region called domains. Within the domain, the magnetic field is intense. A normal sample of iron is not magnetised as the many domains are randomly oriented with respect to one another. Randomly orientated domains However, in the presence of an external magnetic field, say a bar magnet or solenoid, the domains align themselves along the magnetic field to create a unified magnetic field. Aligned domains There are many practical applications of ferromagnetic materials, such as the electromagnet. VCE Physics Unit 3, Area of Study 1, Handout 3 Mr Mark Judd Yr 12 Physics Notes 3.1.3 Page 2 Magnetic Forces Please note that the forces produced by magnets are indeed vector in nature and follow the traditional rules of vector addition and subtraction. You will recall that: 􀁸 Like poles repel (ie. two North or South poles) 􀁸 Opposite poles attract (ie. a North and South pole) Magnetic Fields “A magnetic field describes the property of the space around a magnet that causes an object in that space to experience a force due only to the presence of the magnet.” Field lines drawn around magnets are a visual aid, used to describe the features ofa magnetic field. When drawing field lines, one must obey the following rules: 1. Each field line must leave the North pole, enter the South pole and return to the North pole through the magnet in a continuous loop. 2. Field lines may not intersect 3. The direction of the magnetic at a point is along the tangent to the field line. 4. The closeness of the field lines represents the strength of the magnetic filed 5. Field lines are always directed from the North pole to the South pole NB: Magnetic field strength (B) is measured in Tesla (T). VCE Physics Unit 3, Area of Study 1, Handout 3 Mr Mark Judd Yr 12 Physics Notes 3.1.3 Page 3 Magnetic field around a bar magnet Magnetic field around a current carrying wire VCE Physics Unit 3, Area of Study 1, Handout 3 Mr Mark Judd Yr 12 Physics Notes 3.1.3 Page 4 Magnetic field around a current carrying loop Magnetic field around a solenoid VCE Physics Unit 3, Area of Study 1, Handout 3 Mr Mark Judd Yr 12 Physics Notes 3.1.3 Page 5 Electromagnetism Before Hans Christian Oersted’s discovery in 1820, it was thought that electricity and magnetism were two separate a scientific phenomenon. He discovered that: “A compass needle deflects from magnetic north when an electric current is switched on or off in a nearby wire”. In summary, Oersted stated that: 􀂾 A current carrying wire produces a magnetic field 􀂾 A moving electric charge produces a magnetic field 􀂾 The direction of the field depends upon the direction of the current Diagrammatic Notation When constructing a “bird’s eye” or cross-sectional diagram of a current carrying wire and associated magnetic field, use the following notation: | | Current coming out of the page produces an anticlockwise magnetic field. | | | --- | --- | --- | | | | | | | The dot ( ) is like the head of an arrow heading towards you. | | | | Current going into the page produces a clockwise magnetic field. | | | --- | --- | --- | | | | | | | The cross (􀁵

FAQs

What causes ferromagnetism in materials like iron and nickel?

Ferromagnetism originates at the atomic level, where unpaired electron spins align parallel within regions called domains.

How should magnetic field lines be drawn and what do they represent?

Field lines must leave the North pole, enter the South pole, and form continuous non-intersecting loops; their tangent gives field direction and line closeness represents field strength.

How do the right-hand “Hand Rules” determine magnetic field and force directions?

The right-hand grip rule gives magnetic field direction from current; the right-hand slap rule gives the force direction on a current-carrying wire in a magnetic field; the solenoid rule gives a solenoid’s North pole from current direction.

Sep 20, 2026

Uploaded by James