3.2 KiB
SL Physics - 2
The course code for this page is SPH4U7.
Magnetism
Magnets are objects with north/south dipoles that create a field around them. Although ferromagnetic substances can repel each other, paramagnetic substances are always attracted to a magnetic field. See HL Chemistry#Physics properties of transition elements for more details.
Magnetic fields
(Source:
Kognity)
Similar to electric and gravitational fields, magnetic fields (also known as B-fields) are drawn by their effect on a north pole. Since magnetic poles always appear in equal magnitude pairs, all magnetic field lines for a magnet must form closed loops from north to south outside and south to north inside the magnet. Much like electric field lines, magnetic field lines never touch
(Source:
Kognity)
Atoms in ferromagnetic materials are tiny magnets with dipoles. These dipoles act on neighbouring dipoles and can cause the whole object to align — this is known as an electric domain.
!!! note Nickel, cobalt, or any alloy with nickel, cobalt, or iron can become magnetised this way.
Unmagnetised domains have dipoles pointing in random directions that are aligned when exposed to a magnetic field where they become magnetised domains. As such, bar magnets are always broken into smaller magnets, each with two poles — a monopole is impossible to create.
Straight-line electromagnets
Moving electric charges produce magnetic fields. A circle filled with an “x” indicates that the current is moving away from the viewer in the third dimension while a dotted circle indicates it is moving toward the viewer.
These magnetic fields are centred on the conductor, are in a plane perpendicular to the conductor, and have decreasing magnetic field strength over distance.
(Source:
Kognity)
The right-hand rule for straight-line conductors indicates that when the conductor would be grasped by the right hand, the thumb would point in the direction of current and the fingers pointing in the direction of the magnetic field.
(Source:
Kognity)
Selenoid electromagnets
A selenoid is a conductor coil in a tight helix. Current passed through a selenoid will generate a uniform magnetic field inside the coil with a pattern identical to that of a bar magnet outside it.
(Source:
Kognity)
The right-hand rule can be applied again to a selenoid to identify the direction of the north pole or direction of magnetic field in the coil:
(Source:
Kognity)