Magnetic Fields and Magnetic Force SPH4U

Magnetism Magnetism is an action-at-a-distance force: a magnet creates a magnetic field in the region around it.

Magnetic Field The magnetic field, represented by , is measured in Tesla (T). The Earth’s magnetic field has a magnitude of approximately 25 – 65 mT.

Magnets Magnets have two poles: North and South. Like poles repel; opposite poles attract.

Magnets Magnetic field lines are drawn out of the North pole and into the South.

Permanent Magnets Ferromagnetic materials (such as iron) are made of tiny magnetic domains that can be induced to align.

Electromagnets A magnetic field can also be generated by moving charge (Oersted’s Principle).

Right Hand Rules The direction of the magnetic field can be determined by Right Hand Rules #1 and 2.

Right Hand Rule #1 Point your thumb in the direction of conventional (positive) current flow. Your fingers curl in the direction of the magnetic field lines.

Right Hand Rule #2 Curl your fingers in the direction of conventional (positive) current flow around the loop(s). Your thumb points toward magnetic North.

Magnetic Force Magnetic fields therefore exert force on moving charge: speed of charge angle between velocity vector and magnetic field charge magnetic field

Magnetic Force The direction of the force is given by Right Hand Rule #3: Point your thumb in the direction of the conventional current and your fingers in the direction of the magnetic field. Your palm pushes in the direction of the magnetic force.

Practice What is the direction of the force on the conductor below?

Practice What is the direction of the force on the conductor below? Left

Example An electron travelling at 4.0 x 106 m/s enters a 0.20 T [into the page] magnetic field as shown below. What is the magnitude and direction of the force on the electron?

Example

Example The direction of the force is [down].

More Practice “Magnetic Field Mapping Activity” Textbook Questions