Chapter
19 & 20
Magnetism & Electromagnetic
Induction
Magnetic
Force
Magnetic
Force Right-Hand-Rule
To
find the direction of the magnetic force on a positive charge, start
by pointing the fingers of your right hand in the direction of the
velocity,  .
Now, curl your fingers toward the direction of  .
Your thumb points in the direction of  .
If the charge is negative, the force points opposite to the direction
of your thumb.
An
alternate method- To find the direction of the magnetic force
on a positive charge, start by pointing your first finger of
your right hand in the direction of the velocity, .
Then point your second finger in the direction of the magnetic
field, .
Your thumb points in the direciton of .
If the charge is negative, the force points opposite to the direciton
of your thumb.
Magnitude
of the Magnetic Force, F
(4) 
Example
4
Particle
1, with a charge  and
a speed  ,
travels at right angles to a uniform magnetic field. The magnetic
force it experiences is  .
Particle 2, with a charge  and
a speed  ,
moves at an angle of 55.0° relative
to the same magnetic field. Find (a) the strength
of the magnetic field and (b) the magnitude
of the magnetic force exerted on particle 2.
Solution:
| (a) Find the
magnetic field with particle 1. |
|
| Substitute
values |
|
| (b) Using
the previous answer find the force on particle 2. |
|
Mathematical
way of writing the magnetic force is using a cross product of
vectors:
(5) 
Example
5
A
solenoid is 20.0 cm long, has 200 loops, and carries a current
of 3.25 A. Find the magnitude of the force exerted on a 15.0 µC charged particle moving at 1050 m/s through the interior of
the solenoid, at an angle of 11.5° relative to the solenoid's
axis.
Solution:
| Calculate
the magnetic field. |
|
| Using the
magnetic field find the force on the particle. |
|
Example 6
Three
particles travel through a region of space where the magnetic
field is out of the paper as shown below in the sketch. For each
of the three particles, state whether the particle's charge is
positive, negative, or zero.
Solution:
Particle
1, negative
Particle 2, zero
Particel 3, positive
Example
7
A
particle with a charge of 7.70 µC and a speed of 435 m/s
is acted on by both an electric and a magnetic field. The particle
moves
along the x axis in the positive direction, the magnetic field
has a strength of 3.20 T and points in the positive y direction,
and the electric field points in the positive z direction with
a magnitude of  . Find the magnitude and direction of the net
force acting on the particle.
Solution:
Trajectory
of a Free Particle
(6) 
Example
8
An
electron moving perpendicular to a magnetic field of  follows
a circular path of radius 2.80 mm. What is the electron's speed?
Solution:
Solving
equation (6) for the velocity and then substituting gives:
Video on CRT
Video
on Aurora
Magnectic
Force Part 2
|
