Download Tutorial 3 Magnetostatics

ECT1026 Field Theory
MMU/FOE/ TRIM 1 2010/11
Tutorial 3 Magnetostatics – Part A
Steady Current and Current Density
Q1. Consider a circular, cylindrical, copper conductor of radius 1.025mm. If the wire
carries a current of 0.2A dc, determine the current density in the wire and the
voltage drop across 1m length. [Conductivity of copper wire = 5.8 × 10 7 S/m].
Ampere’s Law
Q2. Current I flow along the positive z-direction in the inner conductor of a long
coaxial cable and returns through the outer conductor. The radius of the inner
conductor is a, and the inner and outer radii of the outer conductor are b and c
respectively.
(a) Determine the magnetic flux density in each of the following regions: r  a,
a  r  b, b  r  c.
(b) Plot the magnitude of B as a function of r.
Q3. A wire carrying a current of 4 A is formed into a circular loop. If the magnetic
field at the center of the loop is 20 A/m, what is the radius of the loop has (a) only
one turn (b) 20 turns?
Magnetic Flux Density
Q4. A charge 1.8 x 10-19 C is moving with a speed of 1 x 106 m/s through a magnetic
field. The magnetic flux density with 3.5 T experiences a magnetic force of
magnitude 2x10-13 N. Determine the angle between the magnetic field and
proton’s velocity?
Biot- Savart Law
Q5. The metal niobium becomes a superconductor with the zero electrical resistance
when it is cooled to below 9 K, but its superconductive behavior ceases when the
magnetic flux density at its surface exceeds 0.12 T. Find the maximum current
that a 0.1 mm diameter niobium wire can carry and remain superconductive.
Magnetic Force
Q6. A charged particle with velocity u is moving in a medium containing uniform


fields E  x E and B  y B . What should u be so that the particle experiences no
net force on it
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