Practise explaining and calculating magnetic force on current-carrying wires and coils, using F = BIL sin theta and Fleming’s left-hand rule for direction.
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.
Two long straight parallel wires P and Q carry currents into the plane of the paper, as shown in Fig. 8.1.
P
The current in P is I and the current in Q is 2 I.
On Fig. 8.1, draw another arrow to show the direction of the force acting on wire Q due to the current in wire P. Label this arrow F.
State how the direction of the force on wire P compares with the direction of the force on wire Q.
Define magnetic flux density.
Electrons are moving in a vacuum with speed . The electrons enter a uniform magnetic field of flux density 4.8 mT . Fig. 6.1 shows the path of the electrons.
Fig. 6.1
The path of the electrons remains in the plane of the page.
State the direction of the magnetic field.
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.
Define magnetic flux density.