5.2.3Electricity and Magnetism

Magnetic Fields

5 min read 4 parts Lesson 26 of 30 1 quiz

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Section 1 of 4Field Lines

Field direction

At any point, the magnetic field direction is the direction in which a north pole would move if placed there.

Field lines

Continuous lines drawn to show the direction and pattern of a magnetic field, running from the north pole to the south pole outside a magnet.

Field strength

The field is stronger where field lines are closer together, and weaker where they are further apart.

Uniform field

A region in which the field lines are parallel and equally spaced, so the field strength is the same everywhere in that region.

Two magnets interact to produce patterns that depend on which poles face each other.

Field Patterns

Neutral point

A point where the fields from two magnets cancel out, so a plotting compass placed there points in no particular direction.

Around a bar magnet

Field lines leave the north pole, curve around the outside, and enter the south pole of the magnet.

Inside a magnet

Inside the magnet the field lines run from the south pole to the north pole, completing each loop.

Unlike poles facing

The field between opposite poles is nearly uniform, with lines running straight from one pole to the other.

Arrangement	Field pattern	Neutral point?
Bar magnet alone	Loops from N to S, strongest at poles	No
Two like poles facing	Lines repel; field curves around each pole	Yes, between the poles
Two unlike poles facing	Lines join N to S, uniform in the middle	No

Place a bar magnet on paper and mark its outline and the positions of its poles.

Place a plotting compass at a point, mark the direction of its north-seeking needle, and draw a short arrow there.

Move the compass to the arrow tip and repeat the marking until the path reaches the other pole or leaves the paper.

Draw smooth continuous lines through the arrows, with the arrows pointing from north to south outside the magnet.

Magnetic field A region in which a magnet or magnetic material experiences a force.
Field line A line showing the direction of a magnetic field, drawn from north to south outside a magnet.
Neutral point A point in a field where the net magnetic field is zero.
Uniform field A field with the same strength and direction at every point in a region.
Field strength The magnitude of the magnetic field, shown by how closely the field lines are spaced.

Drawing field lines that cross each other, which is impossible because the field has only one direction at each point.
Drawing arrows on field lines pointing into the north pole outside the magnet.
Claiming field lines are real physical objects rather than a model used to represent the field.
Saying the field is strongest where field lines are far apart; it is strongest where they are close together.

Transformer Golden Equations Physics Standard

Ratio: V_p / V_s = N_p / N_s = I_s / I_p