FSK 126 Semester 2, 1999

1
Chapter 29 - homework
3E, 5P 19E, 24E - 127 u 33P, 36P - (a) 3.6?10-10
s (b) 1.7?10-4 m (c) 1.5?10-3
m 40E - (a) 1.8?107 Hz (b) 1.7?107 eV 45E, 48P -
(-2.5?10-3j 0.75?10-3k) N
2
Chapter 29 Magnetic fields
29-1 The magnetic field (B)
Charged rod - electric field E Magnet - magnetic
field B Electromagnet - wire coil around iron
core Permanent magnet
How are B-fields setup? Moving electric
charge Elementery particles have intrinsic
magnetic fields
3
29-2 Definition of B
Define B in terms of magnetic force FB exerted on
electrically charged test particle travelling
with v. Magnitude of B
The magnetic force vector

Magnetic force on a particle
Force FB acting on charged particle moving with v
in B is always perpendicular to v and B
4

• Problem
• What is the net force (magnitude and direction)
  on the electron moving in the magnetic field in
  the figure if B  2 T, v  4 x 104 m/s, and
  ? 30o?

Solution
5

• SI unit for B

CP 1
6
Magnetic field lines
Direction of tangent to field lines at point give
direction of B-field at that point. Density of
lines give magnitude of field. Lines from north
pole to south pole Opposites poles -
attract. Like poles - repel

• Sample Problem 29-1
• Hints
• Conversion of kinetic energy of 5.3 MeV
  to J
• (5.3 ? 106 eV)(1.6 ? 10-19)
• 8.48 ? 10-13 J
• angle between v and B is 900
• small force acting on a small mass ? large
  acceleration.

7
(No Transcript)
8
(No Transcript)
9
Summary
10
29-5 A circulating charged particle
11
(No Transcript)
12
Question 12 (pg. 721)
13
Helical Paths
(a) Electron (b) Clockwise
14
29-6 Cyclotrons and Synchrotrons
15
(No Transcript)
16
EP 41E A physicist is designing a cyclotron to
accelerate protons to one tenth the speed of
light. The magnet used will produce a field of
1.4 T. Calculate (a) the radius of the cyclotron
and (b) the corresponding oscillator frequency.
Relativity considerations are not relevant.
qproton  1.602 x 10-19 C mproton  1.67 x 10-27 k
g c 3 x 108 m.s-1
17
29-7 Magnetic Force on a Current-
Carrying Wire
Magnetic field exerts sideways force on moving
electrons in a wire
Magnetic Force on an element of a current
carrying conductor
18
Wire not straight - divide into small straight
segments
-y
EP 51P A long, rigid conductor, lying along the
x-axis, carries a current of 5.0 A in the
negative direction. A magnetic field B is
present, given by B 3.0i 8.0x2j, with x in
meters and B in milliteslas. Calculate the force
on the 2.0 m segment of the conductor that lies
between 1.0 m and 3.0 m.
19
(No Transcript)
20
(No Transcript)