Download Chapter 22

Chapter 22
Magnetism (Lecture II)
Dr. Jie Zou
PHY 1161
1
Outline





Motion of charged particles in a
magnetic field
Magnetic force on a current-carrying
wire
Electric current and magnetic fields
Magnitude of the magnetic field of a
current-carrying wire
Solenoids
Dr. Jie Zou
PHY 1161
2
The Motion of Charged
Particles in a Magnetic Field
The electromagnetic flowmeter
The operating
principle of a mass
spectrometer
Dr. Jie Zou
PHY 1161
3
The Magnetic Force on a
Current-Carrying Wire

Magnitude of the magnetic
force on a current-carrying wire



Direction of the magnetic force
on a current-carrying wire

Dr. Jie Zou
F = ILBsin
I: Current in the wire (A); L:
Length of the wire (m); B:
Magnetic field (T); : The angle
between the direction of the
magnetic field and the current.
Given by the same Magnetic
Force RHR for charges
PHY 1161
4
Example 22-4: Magnetic Levity

A copper rod 0.150 m long
and with a mass of 0.0500
kg is suspended from two
thin, flexible wires. At right
angles to the rod is a
uniform magnetic field of
0.550 T pointing into the
page.

Dr. Jie Zou
Find the direction and
magnitude of the electric
current needed to levitate
the copper rod.
PHY 1161
5
Electric Current and Magnetic
Fields


The source of any
magnetic field is the
motion of electric
charge.
Magnetic field produced
by a straight and
infinitely long currentcarrying wire:


Dr. Jie Zou
PHY 1161
The magnetic field
“circulates” around the
wire.
Find the direction of the
magnetic field using the
magnetic field RHR.
6
Conceptual Checkpoint 22-5

The magnetic field
shown in the sketch is
due to the horizontal,
current-carrying wire.

Dr. Jie Zou
Does the current in the
wire flow to the left or
to the right?
PHY 1161
7
Magnitude of the Magnetic Field
of a Current-Carrying Wire

Magnitude of the magnetic
field, B, produced by a straight
and infinitely long currentcarrying wire:



Dr. Jie Zou
B = (0I)/(2r)
0 = 4 x 10-7 Tm/A, the
permeability of free space.
The field doubles if the current I
is doubled; the field halves if the
distance from the wire, r, is
doubled.
PHY 1161
8
Example 22-6: An Attractive
Wire

A 52-C charged particle
moves parallel to a long wire
with a speed of 720 m/s.
The separation between the
particle and the wire is 13
cm, and the magnitude of
the force exerted on the
particle is 1.4 x 10-7 N.


Dr. Jie Zou
Find the magnitude of the
magnetic field, B.
Find the current in the wire, I.
PHY 1161
9
Solenoids

A solenoid carrying a current
produces an intense, nearly
uniform magnetic field inside the
loops.



Magnitude of the magnetic field
inside a solenoid:


Dr. Jie Zou
A solenoid is also called an
electromagnet.
The magnetic field inside the
solenoid is directed along its axis.
The field outside the solenoid is
almost zero.
B = 0 (N/L) I = 0 nI
n: the number of loops per unit
length
PHY 1161
10
Example 22-7: Through the
Core of a Solenoid

A solenoid is 20.0 cm long,
has 200 loops, and carries
a current of 3.25 A.

Dr. Jie Zou
Find the magnitude of the
force exerted on a 15.0-C
changed particle moving at
1050 m/s through the
interior of the solenoid, at
an angle of 11.5° relative to
the solenoid’s axis.
PHY 1161
11
Homework #7

Chapter 22, P. 793-795, Problems: #31,
33, 49, 57 (Physics, Walker, 4th edition).
Dr. Jie Zou
PHY 1161
12