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.
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.