What you’ll learn3 learning objectivesChoose one objective for a focused lesson, or study the complete topic.20.4.1Magnetic field patterns due to the currents in a long straight wire, a flat• sketch magnetic field patterns due to the currents in a long straight wire, a flat circular coil and a long solenoidSyllabus objective20.4.2The magnetic field due to the current in a solenoid is increased by a• understand that the magnetic field due to the current in a solenoid is increased by a ferrous coreSyllabus objective20.4.3The origin of the forces between current-carrying conductors and determine• explain the origin of the forces between current-carrying conductors and determine the direction of the forcesSyllabus objective