Question

16. A horseshoe magnet, made from two magnets and a steel yoke, is placed on a top pan balance as shown in the upper diagram. A current is passed through a long wire which is fixed. The wire is between, and parallel to, the poles of the magnet, as shown in the lower diagram. 74.87 horseshoe magnet plan view wire balance platform The current is varied. The following values of balance reading m and current I are recorded. I JA 0 1.1 2.2 3.0 4.3 -1.8 m/g 74.87 75.02 75.1775.29 75.46 74.63 a) Write down the relationship between the force F on the wire, the magnetic field B acting on length 1 of the wire, and the current I. b) Explain why the force on the wire is equal in magnitude to the force on the magnet on the top pan balance. [2] c) Use the data to plot a graph to test the relationship between the current and the force it exerts on the magnet. [2] d) What happens when the current is reversed and why? [2] (OCR)

Answer 1

ca) relationship between Force F, Magnetic field B and length I is and current I is F I IB invector ² I ex 4F ( Forle on wire) XB B I N F (b) From newton's 3rd law of Motion. if Magnets apply F force on wire ufwand then wire will also exerts force of same magnitude F, on magnety (pan) downward is co) when current is zero then F =0 then Net force on pan= mg ma mass of Manets. after flow of current Net force Firet = mg + IIB mig m'= mg + IIB m+/Ilo Code) m'= Be g I tm (d) m's effective mass of magnets. When current is renesed the direction of force becomes reverse. "ê becomes -e then force becomes. F=-I (exb) so direction is reversed of forte