Magnetic Phenomena Magnetic Field Magnetic Field

Magnetic Phenomena Magnetic Field

Magnetic Field • • • Experiment on a Magnetic Field Force Lines of a Magnetic Field Law of Biot and Savart Principle of Superposition Magnetic Field along Axis of a Loop with Current • Magnetic Field in a Centre of a Loop with Current • Magnetic Field due to a Current Through a Long Straight Wire

Magnetic Field (continued) • Ampere’s Circulation Law • Intensity of the Magnetic Field Outside and Inside a Straight Wire • Solenoid

Oersted’s Experiment on a Magnetic Field (1819) A magnetic field is said to exist at a point if a compass needle placed there experiences a force. Current gives rise to magnetic fields, just as electric charge gives rise to electric fields.

Force Lines of a Magnetic Field

Force Lines of a Magnetic Field Magnetic field lines of a permanent magnet (a), cylindrical coil (b), iron-core electromagnet (c), straight current-carrying wire (d), and a circular current-carrying loop (e).

Bar magnets Regardless of the shape of magnets (bar magnets, horseshoe magnets, Cshaped magnets) opposite magnetic poles attract each other, and the like magnetic poles repel each other.

Magnetic field of the Earth

Law of Biot and Savart B is called magnetic flux density or magnetic induction, 0 is magnetic constant, is magnetic permeability of a medium.

Superposition Principle

Magnetic Field along Axis of a Loop with Current After adding (integrating) all the vector components caused by all the infinitesimal I dl the total B field will be in a direction along the x-axis. From symmetry we can see that the vectors components in the yz-plane will all cancel leaving only the component of B in the xdirection.

Magnetic Field along Axis of a Loop with Current

Magnetic Field in a Centre of a Loop with Current

Magnetic Field due to a Current Through a Long Straight Wire

Magnetic Field due to a Current Through a Long Straight Wire (cont. ) For a straight wire of final length:

Ampere’s Circulation Law Circulation of the magnetic field intensity round the closed loop is equal to the current enclosed by this loop. - relation between magnetic flux density and magnetic field intensity

Magnetic Field is an Eddy Field • Work along the closed path isn’t zero. • Force lines are closed. • Magnetic field isn’t a potential field, it is an eddy field.

Intensity of the Magnetic Field Outside a Straight Wire

Intensity of the Magnetic Field Inside a Straight Wire

Magnetic Field Caused by Long Current-carrying Solenoid Ampere's law reduces to four straight-line paths of integration. The integral over three of the paths will be zero.

Solenoid - no field outside the solenoid - uniform field inside the solenoid