Transcript Wednesday PowerPoints

W10D2
Important Dates
November 11th, 2010
Veterans Day
November 25th, 2010
Thanksgiving Holiday
December 6th, 2010
Last day of classes
December 7th, 2010
Final exams begin
December 11, 2010
Probable date for 2054 Studio Final
(7:30AM ?)
December 16th, 2010
Grades due on myUCF
 We
continue with magnetism with a study of
induction.
 Next will be inductors.
 Following inductors will be the next
examination.
 Quiz
on Friday
 Problem Session next Monday
 A
Clique
I
I
What is the direction of the magnetic
field due to these two currents at point A?
A
B
C
D
E
Left
Right
In
Out
Other direction
 There
are “natural” magnets (like a compass)
that have a magnetic field associated with
them.
 Electric Currents produce magnetic fields.

Like the field around a wire.
 Moving
charges in a magnetic field
experience forces.
 Electric Currents in magnetic fields also
experience forces (BiL).
 NEXT: CHANGING MAGNETIC FIELDS produce
currents in loops of wire. This is called
induction and this will be started today.
 Chapter

Sections 1-7
 Chapter


21
22
Sections 1-5
Sections 8-9
You should have been reading Chapter 21 and
should begin 22 now
A beam of protons moves in a circle of radius 0.25 m. The protons move
perpendicular to a 0.20-T magnetic field.
(a) What is the speed of each proton?
(b) Determine the magnitude of the centripetal force that acts on each proton.
4.79e+06m/s
1.53e-13N
A particle is going around in a circle in a magnetic field
that is perpendicular to the plane of the circle with a radius r
and a velocity v. If the magnetic field is increased, the
radius will:
A
B
C
D
increase
decrease
remain the same
explode
When beryllium-7 ions (m = 1.165 10-26 kg) pass through a mass
spectrometer, a uniform magnetic field of 0.2503 T curves their
path directly to the center of the detector (see figure below). For
the same accelerating potential difference, what magnetic field
should be used to send beryllium-10 ions (m = 1.663 10-26 kg) to
the same location in the detector? Both types of ions are singly
ionized (q = +e)
A proton with a speed of 3.63 106 m/s is shot into a
region between two plates that are separated by a
distance of 0.24 m. As the drawing shows, a magnetic
field exists between the plates, and it is perpendicular to
the velocity of the proton. What must be the magnitude
of the magnetic field so the proton just misses colliding
with the opposite plate?
0.158
T
Two coils have the same number of circular turns and carry the
same current. Each rotates in a magnetic field as in the figure
below. Coil 1 has a radius of 5.2 cm and rotates in a 0.13-T
field. Coil 2 rotates in a 0.42-T field. Each coil experiences the
same maximum torque. What is the radius (in cm) of coil 2?
Max (sin   0)
 1  NIA1 B1  NIA2 B2
A1 B1   (0.052)2 (0.13)
A2 

 2.6  103 m 2   r22
B2
0.42
r2  2.87  102 m
Suppose in the figure that I1 = I2 = 21 A and that the
separation between the wires is 0.016 m. By applying an
external magnetic field (created by a source other than the
wires) it is possible to cancel the mutual repulsion of the
wires. This external field must point along the vertical
direction.
What is the magnitude of the external
field?
0 I 2 L
F  BIL 
2 D
0 I
4 I   107 4 I  10 7
B


2 D
2 D
2D
4  21  10 7
B
 2.6  10 4 T
2  0.016
D