Summary

• Magnets
• Magnetic fields

• Currents and magnetic fields
  • currents produce magnetic fields applet
  • the right hand rule
    Example #1
    
    Example #2
    
  • fields exert force on currents
  • another right hand rule
    Example #3
    
  • definition of a Tesla
  • force on charges applet
    Example #4
    
    Example #5
    
  
  
  About the photo

klm
A wire carries an electrical current towards the north. In which direction does B point directly above the wire?
A. North           B. South
C. East              D. West
Answer







gc6 20.26
A jumper cable used to start a stalled vehicle carries a 65 A current. How strong is the magnetic field 6.0 cm away from it?
A. 2.17×10^-4 T           B. 6.90×10^-5 T
C. 3.45×10^-5 T           D. 1.38×10^-6 T
Answer







gc6 20.5
The force on a wire carrying 8.75 A is a maximum of 1.28 N when placed between the pole faces of a magnet that are 55.5 cm in diameter. What is the approximate strength of the magnetic field?
A. 1.28 T               B. 0.875 T
C. 0.379 T             D. 0.264 T
Answer







sj6 29.8
If B=50 µT northward and E=100 N/C downward, how do forces on an e^- with velocity 6000 km/s eastward compare?
A. gravity > electric > magnetic
B. electric > gravity > magnetic
C. magnetic > electric > gravity
D. electric > magnetic > gravity
Answer







sj6 29.34
A proton moving in a circular path has a period of 1.00 µs. What is B?
A. 1.00 µT             B. 55.2 µT
C. 33.3 mT             D. 65.6 mT
Answer







 



C. East
Using the right-hand-rule, point your thumb toward the north, the same direction as the current. The curled fingers of your right hand would point east directly above the wire.












 



A. 2.17×10^-4 T













 



D. 0.264 T













 



C. magnetic > electric > gravity













 



D. 65.6 mT










Aurora are formed at the poles of the earth where charged particles from the sun spiral around the magnetic fields of the earth and slam into the atmosphere, ionizing the gas molecules and causing them to emit light. The above photo depicts aurora loops around the southern polar region in the distance as viewed by astronauts onboard the space shuttle.

Here is another photograph of the southern lights taken by astronauts onboard the Space Shuttle Discovery. The emissions, extending nearly vertically upwards, trace out the Earth's magnetic field lines. The green glow occurs at altitudes near 80-120 kilometers. The red glow is less energetic and occurs at altitude above 250 kilometers. Both types of light are produced by oxygen atoms in the atmosphere:


Photos provided courtesy of NASA, Astronaut Overmeyer and Dr. Hallinan. The source of this material is Windows to the Universe at the University Corporation for Atmospheric Research (UCAR). �1995-1999, 2000 The Regents of the University of Michigan; �2000-01 University Corporation for Atmospheric Research. All Rights Reserved.

Of course, auroras are also visible from earth!