asn07_2023
Physics XXXXXXXXXX)
Assignment 7
Due: Thursday, March 23
Hand in to drop slots on second floor of Dunn. Answer in the spaces provided.
Your name (print: Last, First) Your Mark (out of 18)
1. Forces between wires. (Chapter 26, exercise 33) In standard household wiring, parallel wires about 1 cm
apart ca
y cu
ents of about 15 A. What is the force per unit length between these wires? [5]
2. Spiralling electron. In 2.0 s an electron moves 15.0 cm in the direction of a 0.10 T magnetic field. If the
electron's velocity components perpendicular and parallel to the field are equal,
(a) what is the length of its actual spiral trajectory [2], and
(b) how many o
its about the field direction does it complete? [3] Hint: from the velocity components find the
speed, and thus the length of the spiral.
3. Pipes. Consider a long, hollow conducting pipe of radius R
and length L.
(a) A uniform cu
ent flows along the pipe, as shown. Use
Ampère's law to find the magnetic field strength (i) inside and
(ii) outside the pipe. [4]
(b) The same pipe now ca
ies a cu
ent I around the pipe. Again
find expressions for the magnetic field (i) inside and (ii)
outside the pipe. Hint: what configuration does this resemble?
[4]