1. Phy2005 Applied Physics II Spring 2016 Announcements:
Andrea, Bulterman, Crosby, Langley, Powell, Townsend,
Vasilevsky please see or me
Reevaluate your course strategy if you performed poorly
PH office hour tomorrow cancelled (“Gator Day”)

2. Science news page
“Gravitational
Lensing”

3. Last Time
AC vs. DC. The big advantage of AC current is that it is relatively
easy to change the voltage, using a device called a transformer. Power
companies use very high voltages to transmit power over long distances,
then transform down to delivered household voltage of 120V.
Magnetism: magnets always have both N and S poles, as far as we
know. Like poles repel, unlike poles attract:
Magnetic interaction mediated by magnetic field B. Fields lines
emerge from N pole, meet at S pole.

4. B FB = ILB B I Last time cont’d
A wire placed in a perpendicular B-field experiences a sideways force! B I
Field B curls around wire with current I according
to the “right hand rule” B FB
Force on wire in field I
Magnetic field (strength)
[B] = [F/IL]
= Ns/Cm = Tesla
*1 Tesla = 104 gauss
FB = ILB

5. Clicker Quiz Time Log in your remote! ACADEMIC HONESTY
Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.
Log in your remote!

6. Q1 (22.1) A 0.50 T magnetic field is directed vertically downward
into a table top. On the table lies a wire that carries a current of 30A
straight westward. Find the force on a 50-cm length of the wire
due to the field.
7.5 N west
7.5 N south
15 N north
15 N east
15 N west B I E W

7. Q2 A wire is placed perpendicular to the direction of magnetic
field as shown in the figure. The current flows into the page
through the wire. Which arrow represents the correct magnetic
force direction on the wire? B A B C D B D A X C

8. Q3 What is the force acting on the 1 m-long wire placed in a
uniform magnetic field B when current I flows through it as
shown in the figure?
30 I B BI
BItan(30)
BIcos(30)
0.5B

9. X X S N

10. DC Electrical Motor Might get stuck at vertical position
except for angular momentum!! X X X X X X X X
Switched I-direction here! X
Continue to rotate!!! Motor

11. From Wikipedia

13. How do you actually produce this “constant magnetic field”
that we’ve been talking about? B

14. How big a field is produced by a current carrying wire?
A very long wire!: Ampere’s Law B B X r
B = moI/(2pr)
mo = 4 p x 10-7 Tm/A: permeability of vacuum

16. I x o x o x o x o

17. B = monI n: number of turns/m For infinitely long solenoid
For infinitely long solenoid
B = monI
n: number of turns/m

18. A long solenoid magnet has n = 50000 turns/m. If I = 100 A,
B = monI
= (4p x 10-7 Tm/A)(50000 /m)(100 A)
= 6.2 T
IF the total resistance of the magnet wire is 10 Ohm,
P = I2R
= (100)2(10)
= 100,000 W
= 100 kW

19. National High Magnetic Field Laboratory
Bitter Magnet
Electromagnet: Max field approx 33 T
National High Magnetic Field Laboratory
Hybrid Magnet: Electromagnet + Superconducting magnet
World record: 45 T continuous field
@ NHMFL, Tallahassee, FL
However, we can produce much higher field for a very short time:
Pulsed Magnet: 300 T for 6 microsecond
@ NHMFL, Los Alamos National Laboratory
@ NHMFL, Microkelvin Laboratory, UF
15 T but at extremely low temperature 500 microK