(A Level) Magnetic fields and forces

Learning objectives

Describe magnetic fields as fields of force created by moving charges or permanent magnets, and sketch the field patterns around a straight wire, through a flat circular coil and along a solenoid, including the effect of an iron core.

Calculate the force on a current-carrying wire with F = BIL sin θ, find its direction with Fleming's left-hand rule, and define the tesla through the force on a wire carrying unit current per unit length at right angles to the field.

Use F = BQv sin θ for the force on a moving charge, and explain why a charged particle moving at right angles to a uniform field follows a circular path of radius r = mv/(BQ).

Explain how charge carriers deflected sideways in a conductor create a Hall voltage, derive VH = BI/(ntq), and describe how a calibrated Hall probe measures flux density.

Explain how crossed electric and magnetic fields act as a velocity selector that passes only particles with speed v = E/B.

Explain the force between two parallel current-carrying wires as each wire lying in the field of the other, and show that like currents attract and opposite currents repel.