Electromagnetism

Electromagnetism result from moving electrical charge or current. Learn more about the magnetic field produced by a moving charge and its strength.

Magnetism Unit Reminders

In this unit we will follow the current through a wire creating a magnetic field.  In a later section we will learn to calculate variables from givens in a question.

Here are common variables you will see:

Name Variable Unit Unit Symbol
Magnetic Field B Tesla T
Current I Amperes A
Potential Difference (Voltage) V Volts V

Right Hand Rule

A right hand rule is a mnemonic used to memorize a concept.  Right hand rules use parts of your right hand to represent directions of variables.  These variables changes from rule to rule depending on concept.

 

Current Through a Straight Line Wire

Current trough a straight line wire creates a magnetic field that you can use a right hand rule to follow.

Holding your hand in a thumbs up position:

  1. Place your thumb in the direction of current
  2. The north of the compass would follow the direction of the curl of your hand

Hold your pencil in your right hand with the pencil tip the direction of current (your thumb) as you answer questions about current in a straight wire.

 

 

Current Flowing in a Straight Wire Towards You

When current is flowing in a straight line wire towards you a magnetic field is created around the wire.  The direction of this magnetic field can be determined using a right hand rule.  Place your right hand thumb in the direction of current and the resulting curl of your fingers is counterclockwise.  If you placed a compass anywhere around the wire, north would be facing counterclockwise around the wire.

Current in a Straight Wire Flowing Away

Notice the same right hand rule when we turn our hand to follow current away.  When the thumb is away the curl of our hand is now clockwise.  The north of a compass needle placed anywhere around the wire will say clockwise is north.

Compass Around A Current In A Straight Line Wire

Current in a Straight Wire Up

Following the same "thumbs up" hand orientation when your thumb is oriented with current up.  The magnetic field in front of the wire is to the right as seen by the north compass needle.  The magnetic field behind the wire is left as seen looking at the north compass needle.

Compass Around A Current In A Straight Line Wire

Current in a Straight Wire Down

Following the same hand orientation when your thumb is oriented with current down.  The magnetic field in front of the wire is to the left as seen by the north compass needle.  The magnetic field behind the wire is right as seen looking at the north compass needle.

Example Problems

1. What direction is the magnetic field above a wire when current flows towards you?

Left

Current Towards You

2. What direction is the magnetic field to the right of a wire when current flows away from you?

Down

Magnetic Field Current Away

3. What direction is the magnetic field in front of a wire when current flows up?

Right

Magnetif Field Current Up

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