On completion of this unit the student should be able to analyse gravitational, electric and magnetic fields, and apply these to explain the operation of motors and particle accelerators, and the orbits of satellites.
Key knowledge
Fields and interactions
- the shape of the field
- the use of the inverse square law to determine the magnitude of the field
- potential energy changes (qualitative) associated with a charge moving in the field
- potential energy changes in a uniform electric field: W = qV,
- the magnitude of the force on a charged particle due to a uniform electric field: F = qE
- the radius of the path followed by an electron in a magnetic field: , where v << c
Application of field concepts
Key knowledge
Fields and interactions
- describe magnetism and electricity using a field model
- investigate and compare theoretically and practically magnetic and electric fields, including directions and shapes of fields, attractive and repulsive effects, and the existence of dipoles and monopoles
- investigate and compare theoretically and practically electrical fields about a point mass or charge (positive or negative) with reference to:
- the shape of the field
- the use of the inverse square law to determine the magnitude of the field
- potential energy changes (qualitative) associated with a charge moving in the field
- investigate and apply theoretically and practically a field model to magnetic phenomena, including shapes and directions of fields produced by bar magnets, and by current-carrying wires, loops and solenoids
- identify fields as static or changing, and as uniform or non-uniform
- analyse the use of an electric field to accelerate a charge, including:
- potential energy changes in a uniform electric field: W = qV,
- the magnitude of the force on a charged particle due to a uniform electric field: F = qE
- analyse the use of a magnetic field to change the path of a charged particle, including:
- the radius of the path followed by an electron in a magnetic field: , where v << c
Application of field concepts
- describe the interaction of two fields, allowing that electric charges, magnetic poles and current carrying conductors can either attract or repel, whereas masses only attract each other
- investigate and analyse theoretically and practically the force on a current carrying conductor due to an external magnetic field, F = nIlB, where the directions of I and B are either perpendicular or parallel to each other
- investigate and analyse theoretically and practically the operation of simple DC motors consisting of one coil, containing a number of loops of wire, which is free to rotate about an axis in a uniform magnetic field and including the use of a split ring commutator
- investigate, qualitatively, the effect of current, external magnetic field and the number of loops of wire on the torque of a simple motor
- model the acceleration of particles in a particle accelerator (including synchrotrons) as uniform circular motion (limited to linear acceleration by a uniform electric field and direction change by a uniform magnetic field).
