28. Magnetic Fields and Forces

A flat, square surface with side length $3.40\mathrm{cm}$ is in the xy-plane at $z=0$. Calculate the magnitude of the flux through this surface produced by a magnetic field $B=\left(0.200T\right)i+\left(0.300T\right)j-\left(0.500T\right)k$.

Which statement correctly describes $B$ field lines?

When a compass is used near a bar magnet, what does the compass needle align with?

Which of the following statements about magnetic fields is true?

A Hall probe, consisting of a rectangular slab of current-carrying material, is calibrated by placing it in a known magnetic field of magnitude 0.10 T. When the field is oriented normal to the slab’s rectangular face, a Hall emf of 12 mV is measured across the slab’s width. The probe is then placed in a magnetic field of unknown magnitude B, and a Hall emf of 63 mV is measured. Determine B assuming that the angle θ between the unknown field and the plane of the slab’s rectangular face is (a) θ = 90°, and (b) θ = 60°.

Which type of magnet can have its polarity reversed?

Which of the following materials would be attracted by a magnet?

A long straight wire carries a current upward. At a point located to the east of the wire, what is the direction of the magnetic field produced by the current at that point?

Which of the following materials is attracted to a magnet?