(455) Magnetic fields, hand rules for wire and solenoid [IB Physics SL/HL]

Magnetic Fields

• Definition: Area around a magnet where magnetic forces can be felt.

• Magnetic field lines indicate direction of force and are drawn from the north to the south pole of a magnet.

Compass and Magnetic Direction

• A compass points north, influenced by Earth's magnetic field.

• In real life, compasses rotate, allowing navigation.

• North and south of magnets: Unlike electric charges (which can exist independently), magnetic poles cannot exist alone (no magnetic monopoles).

  • Cutting a magnet always yields a north and a south pole.

Drawing Magnetic Field Lines

• Magnetic field lines can be visualized around a bar magnet:

  • Lines originate from North and terminate at South.

  • Density of lines indicates strength of the field.

• Earth acts like a giant bar magnet:

  • Earth's magnetic north is actually a magnetic south pole because compasses point towards it.

Electromagnetism

• Electric and magnetic fields are interrelated; this is known as electromagnetism.

• Electric current creates magnetic fields, and they coexist.

Right-Hand Rule (RHR) for Electric Current

• Thumb: Direction of current flow.

• Fingers: Direction of magnetic field.

• Drawing magnetic field lines around a wire:

  • If the current is out of the page, thumb points out and fingers curl counterclockwise.

  • If the current is into the page, thumb points in and fingers curl clockwise.

Example: Current Wire

• Current directed out of the page: Draw field lines counterclockwise.

• Current directed into the page: Draw field lines clockwise.

Solenoid and Right-Hand Rule

• A solenoid is a coil of wire producing a magnetic field when current flows:

  • Thumb: Direction of magnetic field.

  • Fingers: Curl in the direction of the current.

  • Determine North/South direction based on the magnetic field's orientation.