Phys 208 - Recitation E-Fields

Magnetic Fields - Phys 208
1. Fields
1.1 Draw some fields
Below are 6 configurations of wires carrying currents of equal magnitudes into or out of the page,
depending on the indicated symbol. Sketch field vectors showing the direction and relative
strengths of the magnetic fields created by these current carrying wires. If the magnetic field is zero
anywhere, locate that point and indicate it.
1.2 Draw some more fields
Below are 3 configurations of wires carrying currents of equal magnitudes in the plane of the page,
depending on the indicated arrow. Use dots (·) and crosses (×) to indicate the direction of the
magnetic fields in the boxes.
1.3 A floating rod
A constant magnetic field, , is directed horizontally, parallel to the ground. A straight segment of
copper wire, with mass density and diameter , is also parallel to the ground and perpendicular to
the magnetic field. Determine the amount of current, in terms of the physical parameters of the
system, that will cause the rod to levitate. (That's another way of saying the magnetic force balances
the gravitational force)
1.4 An cyclotron orbit
An electron is accelerated from rest through a potential difference of 500 V, then injected into a
uniform magnetic field. Once in the magnetic field, it completes half a revolution in 2.0 ns. What is
the radius of its orbit?
1.5 Hall Effect
A Hall probe consists of a strip of the metal bismuth that is 0.15 mm thick and 5.0 mm wide. The
charge carrier density in Bismuth is
. The Hall voltage on the probe is 2.5 mV
when the current through it is 1.5 A. What is the strength of the magnetic field, and what is the
electric field strength inside the bismuth?