|
ID/Type |
Web Link or WA Question Code |
Local download |
Launch from browser |
Description |
|
L23-2 |
L23-2-03 |
em-ratio-1c.iwp |
em-ratio-1c.iwp |
An electron is accelerated from rest under the influence of a potential V1 (not shown). At the origin, the electron enters a uniform magnetic field produced by Helmholtz coils. Within the area encircled by the coils, the electron follows a circular path. |
|
L23-3 |
L23-3-02 |
em-ratio-1d.iwp |
em-ratio-1d.iwp |
An electron is accelerated from rest under the influence of a potential V1 (not shown). At the origin, the electron enters crossed electric and magnetic fields. The electric field is oriented in the -y direction and is produced by parallel plates with a potential difference equal to V2. The magnetic field is oriented in the -z direction (into screen) and is produced by Helmholtz coils. |
|
L23 |
Theory and Design
(Introduction) |
em-ratio-2d.iwp |
em-ratio-2d.iwp |
An electron is accelerated from rest and enters an electric field produced by parallel plates with a constant potential difference across them. |
|
L23 |
Theory and Design
(Case 1) |
em-ratio-1b.iwp |
em-ratio-1b.iwp |
An electron is accelerated from rest under the influence of a
potential V1 (not shown). At the origin, the electron enters a uniform electric
field. The electric field is oriented in the -y direction and is produced by
parallel plates with a potential difference equal to V1. |
|
L23 |
Theory and Design
(Case 2) |
em-ratio-1c.iwp |
em-ratio-1c.iwp |
An electron is accelerated from rest under the influence of a
potential V1 (not shown). At the origin, the electron enters a uniform magnetic
field produced by Helmholtz coils. Within the area encircled by the coils, the
electron follows a circular path. |
|
L23 |
Theory and Design
(Case 3) |
em-ratio-2d.iwp |
em-ratio-2d.iwp |
An electron is accelerated from rest and enters an electric field produced by parallel plates with a constant potential difference across them. |
|
E.22.01c |
APB-22-01-05b |
magforce-03.iwp |
magforce-03.iwp |
Four particles of equal mass and equal magnitudes of velocity have different charges. Run the applet to see how the particles move in a uniform magnetic field pointed perpendicularly out of the screen. Which particles are negative and which are positive? |
|
E.22.01c |
APB-22-01-09b |
magforce-06.iwp |
magforce-06.iwp |
Three particles of equal mass and magnitude of velocity move in a uniform magnetic field pointed perpendicularly out of the screen. Rank the particles in increasing order according to the magnitude of their charge. |
|
E.22.01c |
APB-22-01-13t |
magforce-08.iwp |
magforce-08.iwp |
The view is that of an observer in space looking down on one of the poles of the Earth. An electron orbits the Earth at the equator under the influence of the magnetic force due to the Earth's magnetic field. The gravitational force on the electron can be ignored in comparison to the magnetic force. Which pole, magnetic north or south, is directly below and nearest the observer? |
|
E.22.01c |
magforce-09.iwp |
magforce-09.iwp |
magforce-09.iwp |
An electron moves under the influence of a uniform magnetic field directed perpendicularly outward from the screen. What must the direction and magnitude of a uniform electric field be such that the net force on the electron is 0 at the origin? |
|
E.2202t |
Magnetic Force on
a Wire |
motor-01.iwp |
motor-01.iwp |
A DC motor requires for its operation a magnetic field, a loop of
wire that can turn on an axis, and a source of current. With the correct
orientation of the loop in the field, the loop will turn when a current is
passed through it. For the simple motor shown above, the magnetic field crossing
the loop from N to S poles is nearly uniform and is represented by the light
gray lines. Sides 1 and 3 of the loop experience opposing magnetic forces
directed out of and into the screen. Since these forces have lines of action
that do not pass through the axis of rotation, the forces create torques which
cause the loop to rotate. (Note that sides 2 and 4 may also experience magnetic
forces. However, these forces act parallel to the axis of rotation and do not
create torques.)
In order for the loop to always rotate in the same sense, the current must
always travel around the loop in the same sense (counterclockwise in this case).
This is achieved with an arrangement of brushes called a split ring commutator.
The brushes are electrical contacts around which the wire leads from the loop
slide. Note the insulating gap between the brushes. This has the function of
breaking the current momentarily every half cycle. (Although the current is
momentarily 0, the loop continues rotating due to its inertia.) Follow, for
example, side 1 as the loop rotates through a half turn. Initially the current
in side 1 is down. In order for the loop to continue to rotate after a half
turn, the current in side 1 has to be up when side 1 has replaced side 3 on the
right. This reversal is achieved with the commutator. Step the animation through
frame-by-frame as the brushes reach the insulating gap in order to see what
happens. Note that the current is always up on the right side and down on the
left side. |
|
E.2202t |
Magnetic Force on
a Wire |
motor-03.iwp |
motor-03.iwp |
This is a view of a DC motor looking down on the loop. (The line
of sight is parallel to the plane of the loop.) The direction of current in the
side of the loop nearest the observer is shown by the black arrow. The numbers 1
and 3 indicate the sides of the loop perpendicular to the screen. Initially, the
current goes into the screeen on side 1 and comes out of the screen on side 3.
By the RHR, the magnetic force on side 1 is down the screen initially while that
on side 3 is up the screen (red vectors). These forces are constant in
magnitude, since the field, current, length of side, and angle between the
current and the field are all constant.
Run the applet now. The blue vectors that appear are the components of the
forces perpendicular to the wire. These components produce the torque on the
loop. Note that these components vary in both magnitude and direction as the
loop turns. As a result, the net torque on the loop changes with time, and this
causes the loop to rotate with a varying angular frequency, although the
animation isn't sophisticated enough to show this. A practical motor would be
engineered so as to produce a constant angular frequency.
Note that when the loop has rotated through 90 degrees, the current switches
from down to up. This switching is accomplished with a split ring commutator
which isn't shown. The switch is necessary so that the forces also switch and
keep the loop rotating in the same direction. Another such switch occurs at the
270 degree position. |
|
M10at |
APB-M10a-01tut |
cp-efield-02.iwp |
cp-efield-02.iwp |
A charged particle moves under the influence of an electric field oriented along the y-axis. Note this sign convention: The direction of positive E is +y (toward top of screen) The red and blue vectors on the particle represents its velocity and acceleration. |
|
M10bt |
APB-M10b-01t |
cp-mfield-02.iwp |
cp-mfield-02.iwp |
A charged particle moves under the influence of a magnetic field oriented along the z-axis (perpendicular to the screen). The direction of positive B is +z (outward from screen). The blue vector on the particle represents its acceleration. |
|
M10bt |
APB-M10b-11t |
cp-mfield-02.iwp |
cp-mfield-02.iwp |
A charged particle moves under the influence of a magnetic field oriented along the z-axis (perpendicular to the screen). The direction of positive B is +z (outward from screen). The blue vector on the particle represents its acceleration. |
|
M10bt |
APB-M10b-14t |
mass-spec.iwp |
mass-spec.iwp |
Two singly-ionized isotopes of the same element are injected at the same velocity into a region of uniform magnetic field pointing out of the screen. (There is no field below the x-axis). Determine the ratio of the masses of the isotopes. |
|
M10ct |
APB-M10c-01t |
velocity-selector-02.iwp |
velocity-selector-02.iwp |
A charged particle moves under the influence of an electric field oriented along the y-axis and a magnetic field oriented along the z-axis. Sign conventions:
positive E is +y (toward top of screen)
positive B is +z (outward from screen)
Vectors: red = velocity blue = acceleration |
|
M10a-2 |
Charged Particle
in an Electric Field |
cp-efield-02.iwp |
cp-efield-02.iwp |
A charged particle moves under the influence of an electric field oriented along the y-axis. Note this sign convention: The direction of positive E is +y (toward top of screen) The red and blue vectors on the particle represents its velocity and acceleration. |
|
M10b-2 |
Charged Particle
in a Magnetic Field |
cp-mfield-02.iwp |
cp-mfield-02.iwp |
A charged particle moves under the influence of a magnetic field oriented along the z-axis (perpendicular to the screen). The direction of positive B is +z (outward from screen). The blue vector on the particle represents its acceleration. |
|
M10b-2 |
Charged Particle
in a Magnetic Field |
mass-spec.iwp |
mass-spec.iwp |
Two singly-ionized isotopes of the same element are injected at the same velocity into a region of uniform magnetic field pointing out of the screen. (There is no field below the x-axis). Determine the ratio of the masses of the isotopes. |
|
M10c |
Charged Particle
in Electric and Magnetic Fields |
velocity-selector-02.iwp |
velocity-selector-02.iwp |
A charged particle moves under the influence of an electric field oriented along the y-axis and a magnetic field oriented along the z-axis. Sign conventions: positive E is +y (toward top of screen)
positive B is +z (outward from screen)
Vectors: red = velocity blue = acceleration |