P3.3 Magnets and magnetic fields
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P3.3 Magnets and magnetic fields
Mathematical learning outcome:
PM3.3i apply: force on a conductor (at right angles to a magnetic field) carrying a current (N) = magnetic flux density (T) x current (A) x length (m)
Assessable content statements:
P3.3a describe the attraction and repulsion between unlike and like poles for permanent magnets
P3.3b describe the difference between permanent and induced magnets
P3.3c describe the characteristics of the magnetic field of a magnet, showing how strength and direction, change from one point to another
P3.3d explain how the behaviour of a magnetic (dipping) compass is related to evidence that the core of the Earth must be magnetic
P3.3e describe how to show that a current can create a magnetic effect and describe the directions of the magnetic field around a conducting wire
P3.3f recall that the strength of the field depends on the current and the distance from the conductor
P3.3g explain how solenoid arrangements can enhance the magnetic effect
P3.3h describe how a magnet and a current carrying conductor exert a force on one another
P3.3i show that Fleming’s left-hand rule represents the relative orientations of the force, the current and the magnetic field
P3.3j apply the equation that links the force on a conductor to the magnetic flux density, the current and the length of conductor to calculate the forces involved
P3.3k explain how the force exerted from a magnet and a current-carrying conductor is used to cause rotation in electric motors
A simple Key Stage 3 experiment of separating a variety of different materials as either magnetic or non-magnetic to recap and become familiar with the materials, which are magnetic. There are many Key Stage 3 practicals that will allow learners to quickly recap Key Stage 3 concepts P3.3a–d on the Institute of Physics website.
Learners should be familiar with the magnetic field around a current carrying wire. It can become confusing when looking at the field around a solenoid. Learner resource 1 contains tasks, which will simplify the understanding of a solenoid and its magnetic field.
Common misconceptions or difficulties learners may have
P3.3a - Learners have an automatic assumption that all metals are magnetic. Learners can be provided with a variety of materials (clearly labelled), which include iron, nickel and cobalt, as well as many other non-magnetic materials. Learners are to use magnets and place the materials into either a magnetic or non-magnetic category.
P3.3c – A common misconception learners have is that only magnets produce magnetic fields. When explaining magnetic fields key terminology and explanations need to be clear and use of diagrams to aid understanding.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course
P3.3 magnetic fields is an introduction to other topics such as global challenges (P6.2c, d, e). Magnetic fields are critical in transformers and its understanding will make it easier for learners in future topics.
The knowledge and understanding of ‘Magnetic fields’ builds on the work covered previously in section P3.1e on current.
The task allows learners to independently build up knowledge on solenoids. They should be able to draw its magnetic field and explain what affects its strength.
The task is aimed at learners who are familiar with magnetic field around a straight wire but now need to look at a solenoid and its magnetic field.
Learners have three tasks, each task builds slowly from the previous until they are able to draw its magnetic field and explain what affects its strength.
Task 1 learners become familiar with soft iron increases magnetic field; task 2 learners become familiar with more turns gives stronger magnetic field. The last task learners use the hint and draw the magnetic field around a solenoid.
Approaches to teaching the content
Learners could be given the scenario of a wizard who rules the lands and wishes to enslave the villages by using magic. However, it is not magic but the use of electricity and magnetism. Learners must use their expertise on magnetism and electricity to help persuade the villagers that it’s not magic but simple trickery of science. Learners must plan a speech, which will be delivered to the villages, which explains magnets and magnetic fields. Learners are to present to the group.
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