(j) Electromagnetism

Learning Objectives

draw the pattern of magnetic field due to currents in straight wires and in solenoids and state the variation in magnetic field strength over different parts of the pattern
state the effect of changing the magnitude and/or direction of the current on the magnetic field
describe the applications of the magnetic effect of a current in a circuit breaker
describe an experiment to show the force on a current-carrying conductor, and on a beam of charged particles in a magnetic field, including the effect of reversing the (i) current (ii) direction of the field
deduce the relative directions of force, field and current when any two of these quantities are at right angles to each other using Fleming’s left-hand rule
describe the field patterns between currents in parallel conductors and relate these to the forces which exist between the conductors (excluding the Earth’s field)
explain how a current-carrying coil in a magnetic field experiences a turning effect and how this is affected by the (i) number of turns in the coil (ii) current
discuss how this turning effect relates to the action of an electric motor
describe the action of a split-ring commutator in a two-pole, single coil motor and the effect of a soft-iron cylinder
*show an understanding of similarities and differences between d.c. motor and a.c. motor

Magnetic effect of a current

Oersted's Experiment - JavaLabOersted's experiment Oersted, a Danish physicist, accidentally discovered the occurrence of a magnetic field around a current-carrying wire. Oersted said that he was surprised to see the compass's magnetic needle placed next to the wire rotate while experiment to show...

https://javalab.org/en/oersteds_experiment_en/

https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/orsted-s-compass

Magnetic field around a straight current carrying conductor

A magnetic field is produced when a current flows through a conductor.

The magneic field is circular and strongest around the wire but becomes weaker as the distance from the wire is increased as shown by incresing separation between successive circular magnetic force lines.

The strength of the magnetic field produced by a current-carrying wire is increases by increasing the magnitude of the current flowing through it.

The direction of the magnetic field around the wire is given by