Practise analysing magnetic fields, forces on conductors and charges, Hall and velocity-selection applications, magnetic flux and electromagnetic induction.
State what is meant by a magnetic field.
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.
A second long, straight wire Q, carrying a current of 5.0 A out of the page, is placed parallel to wire P , as shown in Fig. 6.2.
Fig. 6.2
The flux density of the magnetic field at wire Q due to the current in wire P is 2.6 mT .
Calculate the magnetic force per unit length exerted on wire Q by wire P.
force per unit length =
State the direction of the force exerted on wire Q by wire P.
The flux density of the magnetic field at wire P due to the current in wire Q is 1.5 mT . Determine the magnitude of the current in wire P. Explain your reasoning.
current = A
Define magnetic flux density.
An insulated rectangular coil of wire, consisting of 40 turns, is suspended in a cradle from a newton meter, as shown in Fig. 7.1.
Fig. 7.1
The vertical sides of the coil have a length of 5.00 cm and the horizontal sides have a length of 3.00 cm . The initial reading on the newton meter is 0.563 N .
A U-shaped magnet rests on a top-pan balance that is set to a reading of 0.00 g . The lower edge of the coil is lowered into the region between the poles of the U-shaped magnet, as shown in the side view in Fig. 7.2.
Fig. 7.2
The magnetic field in the region between the poles is uniform.
The lower edge of the coil is entirely within the uniform magnetic field.
A current of 3.94 A is now passed through the coil. This causes the reading on the top-pan balance to change to 2.16 g .
Explain why the current causes a vertical force to act on the coil.
Determine, to three significant figures, the flux density B of the uniform magnetic field.
Determine what is now the reading on the newton meter. Explain your reasoning.
A slice of a conducting material has its face QRLK normal to a uniform magnetic field of flux density B, as illustrated in Fig. 8.1.
Fig. 8.1
Electrons enter the slice travelling perpendicular to face PQKJ.
For the free electrons moving in the slice:
state the direction of the force on an electron due to movement of the electron in the magnetic field
identify the faces, using the letters on Fig. 8.1, between which a potential difference is developed.
face and face
Explain why the potential difference in (a)(ii) reaches a maximum value.
The number of free electrons per unit volume in the slice of material is . The thickness PQ of the slice is 0.10 mm .
The magnetic flux density B is .
Calculate the potential difference across the slice for a current of .
potential difference = V
The slice in (c) is a metal.
By reference to your answer in (c), suggest why Hall probes are usually made using semiconductors rather than metals.
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.