Practise sketching field patterns around wires, coils and solenoids, identifying directions and explaining ferrous-core enhancement and forces between currents.
A long, straight wire P carries a current into the page, as shown in Fig. 6.1.
Fig. 6.1
On Fig. 6.1, draw four field lines to represent the magnetic field around wire P due to the current in the wire.
An ideal transformer is shown in Fig.9.1.
Fig. 9.1
Explain
why the core is made of iron,
A long air-cored solenoid is connected to a power supply, so that the solenoid creates a magnetic field. Fig. 6.1 shows a cross-section through the middle of the solenoid.
Fig. 6.1
The direction of the magnetic field at point W is indicated by the arrow. Three other points are labelled X, Y and Z .
On Fig. 6.1, draw arrows to indicate the direction of the magnetic field at each of the points 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.