State the two conditions that must be satisfied for a copper wire, placed in a magnetic field, to experience a magnetic force.
A long air-cored solenoid is connected to a power supply so that the solenoid creates a magnetic field. The figure below shows a cross-section through the middle of the solenoid.
The direction of the magnetic field at point W is indicated by the arrow. Three other points are labelled X, Y and Z. Compare the magnitude of the flux density of the magnetic field:
at X and at W
at Y and at Z.
Two long parallel current-carrying wires are placed near to each other in a vacuum. Explain why these wires exert a magnetic force on each other. You may draw a labelled diagram if you wish.
