Magnetic Induction

Magnetic induction occurs when motion of a wire through a changing strength of magnetic field (magnetic flux) creates a current.  The motion induces a voltage and an electrical force that pushes electrons through the wire.

Induction means you are performing an action to create something.  In this case you are moving a wire to create current.

Magnetic Flux

Magnetic Flux is a measure of the number of magnetic field lines passing through a given point.  The more magnetic field lines the stronger the flux and interaction with other magnets and ferromagnetic materials.  The magnetic flux must be changing to induce a current in a conductive wire.

Magnetic Flux

Magnetic Induction

Magnetic induction also called electromagnetic induction occurs when motion is through a changing magnetic field (magnetic flux).

Moving a wire perpendicular a magnetic field produced by the U shaped magnet in the animation forces current through a wire.

Magnetic induction is the principle behind an electric generator that turns mechanical energy (motion) into electric energy.

  • Motion of a wire in a through a changing magnetic flux (changing magnetic field) induces a voltage.
  • Motion induced voltage causes current to run through the wire.
  • The amount of voltage and current is proportional to the speed and the strength of the changing magnetic field.

Three Ways to Increase Current Through Magnetic Induction

Three ways to increase the voltage and current through electromagnetic induction:

  1. Increase the relative motion through a changing magnetic field
  2. Increase the strength of magnets producing the magnetic field
  3. Use a solenoid and increase the number of coils

Indirectly anything that would decrease resistance would also increase the induced current.

Perpendicular motion to the magnetic field created by the U shaped magnet creates no current since there is no change in magnetic flux (strength of magnetic field).  Moving a wire at angle other than perpendicular would produce less current.  Moving a wire in an unchanging magnetic field (magnetic flux) creates no current.

Example Problem

1. Which of the following would be occurring if you rotated a loop of wire in a magnetic field as seen here?

A. The loop will be squished from the induced magnetic force

B. The magnetic field would be strengthened

C. Nothing, since you don't have a straight wire

D. A current would be produced in the wire

D. A current would be produced in the wire

The relative motion of the loop of wire in a magnetic field would induce a current in a wire.

Magnetic Induction Right Hand Rule

When the fingers point in the direction of the south pole, and the thumb points in the direction of motion of the wire, the palm is in the direction of the induced current.

  • Fingers: align your fingers toward the south pole
  • Thumb:  align your thumb with the direction of motion
  • Palm: your palm will be aligned with the direction of induced current
Magnetic Induction Right Hand Rule

Example Problems

2. Which of the following would not increase the current produced in a wire?

A. Having a stronger magnet

B. Having a solenoid with more coils

C. Moving a wire slower

C. Moving the wire slower

3. Which way would current flow when a wire is moved upwards perpendicular to a magnetic field produced by the magnet seen below?

Magnetic Induction Question

Away from you

When you align your hand with the thumb (motion) up and fingers to the right (aligned with the south pole), your palm (current) will face away from you.

Magnetic Induction Question Solution

4. What pole of the magnet is labeled with the question mark when current flows away while you move a wire upwards?

Magnetic Induction Question

North Pole

When you align your hand with the thumb (motion) up your palm (current) away from you, your fingers face to the right (south pole) and the opposite side would be the north pole.

Electromagnetic Induction Question Solution

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