Third exam Thursday, April 23
105, 107 Heldenfels
7 pm – 8 pm
The force on a charge q moving with a velocity F
v
)( BvEqF
The magnitude of the force
sinqvBF
sec)//(][ meterCoulombNewtonsB
gausssmCNewtonmwteslaT 42 10//1/1)(1
TGaussBEarth4101
left-hand ruleright-hand rule
BsidFd
Small peace of wire
Ampere’s Law
irdB 0
The field produced by an infinite wire
a
iB
2
0
Biot-Savart Law
3
)(
r
rsdiBd
Infinitesimally small element of a current carrying wire produces an infinitesimally small magnetic field
Sd
i
(Also called Ampere’s principle)
30 )(
4 r
rsdiBd
r
0 is called permeability of free space
2770 )/(104)/(104 ampNmeterampwebers
Faraday’s Law of Induction
The induced EMF in a closed loop equals the negative of the time rate of change of magnetic flux through the loop
dt
dEMF B
Test 3 results Average 77Median 849 perfect scores
>90 >80 >70 >60 >50 <50
39
1310 10 9 11
In the circuit below, suppose the switch has been in position A for a very long time. If it is then switched to B at t=0, find the current as a function of time.
A
B+
_
LRV
Make your own MOTOR!
All you need is a battery, a nail, a small magnet, and a wire (foil works better)
http://en.wikipedia.org/wiki/Homopolar_motor
General Atomics is developing a full-scale, 36.5-megawatt, 120-rpm superconducting DC homopolar motor for ship propulsion.
• Significantly quieter, smaller, and lighter than AC motors• More efficient than the AC motor systems• Control is more straightforward and simpler than the AC motor systems• Suited to simpler and less costly ship electrical distribution architectures
http://atg.ga.com/EM/defense/dc-motor/index.php
Magnetic MaterialsDiamagnetism: The magnetic field caused by current loops is always opposite in the direction to that of the external field.
Paramagnetism: When such a material is placed in a magnetic field, the field exerts a torque on each magnetic moment, . These torques tend to align the magnetic moments with the field. In this position, the directions of the current loops are such as to add to the externally applied magnetic field.
Ferromagnetism: iron, nickel.. Magnetic moments line up parallel to each other in magnetic domains even without external field. Without field they are randomly oriented. When field is applied, the domains tend to orient themselves parallel to the field.
Water Nitrogen Oxygen
Boils
Freezes
100 °C (212 F) -196 °C (-322 F) -183 °C (-297 F)
0 °C (32 F) -210 °C (-346 F) -223 °C (-369 F)
Our air is ¾ Nitrogen and ¼ Oxygen
• 1908- liquefied helium produced
• First discovered in mercury by Kamerlingh-Onnes in 1911.
• Critical temperature 4.21K.
• Nobel Prize in 1913.
Superconductivity
High-Tc Superconductivity
Liquid nitrogen temperature 77 K
Complex ceramic materials were discovered in 1986. They exhibit superconductivity at much higher temperatures – above LN temperature!
Muller and Bednortz, Nobel Prize 1987
Superconductivity
Kamerlingh-Onnes 1911
Meissner effect and magnetic levitation
Type I superconductor Type II superconductor
Vortices