Practise sketching field patterns around wires, coils and solenoids, identifying directions and explaining ferrous-core enhancement and forces between currents.
A long straight vertical wire A carries a current in an upward direction.
The wire passes through the centre of a horizontal card, as illustrated in Fig. 10.1.
Fig. 10.1
The card is viewed from above. The card is shown from above in Fig. 10.2.
Fig. 10.2
On Fig. 10.2, draw four lines to represent the magnetic field produced by the current-carrying wire.
Two wires A and B are now placed through a card. The two wires are parallel and carrying currents in the same direction, as illustrated in Fig. 10.3.
Fig. 10.3
Explain why a magnetic force is exerted on each wire.
State the directions of the forces.
The currents in the two wires are not equal.
Explain whether the magnetic forces on the two wires are equal in magnitude.
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.
A long straight vertical wire A carries a current in an upward direction.
The wire passes through the centre of a horizontal card, as illustrated in Fig. 10.1.
Fig. 10.1
The card is viewed from above. The card is shown from above in Fig. 10.2.
Fig. 10.2
On Fig. 10.2, draw four lines to represent the magnetic field produced by the current-carrying wire.
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.