Summary


























klm
In the circuit segment shown, if C = 5.0 µF, Q = 15 µC, ℰ = 6.0 V, R = 4.0 Ω, and I = 3.0 A, what is the potential difference Vb − Va? circuit segment
A. +21.0 V
B. +9.00 V
C. +6.00 V
D. −3.00 V
Answer



















POP5 22.6
If B = 50 µT northward and E = 100 N/C downward, how do the magnitudes of the forces on an electron compare if it has a velocity of 6000 km/s eastward?
A. gravity < electric < magnetic
B. electric < gravity < magnetic
C. electric < magnetic < gravity
D. magnetic < electric < gravity
Answer



















PSE6 29.32
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



















POP5 22.43
What is the net force exerted on the loop if I1 = 5.00 A, I2 = 10.0 A, c = 0.100 m, a = 0.150 m, and l = 0.450 m? Serway POP4 Figure P22.35
A. 27.0 µN right
B. 27.0 µN left
C. 923 µN right
D. 923 µN left
Answer























PSE6 29.14
A conductor with mass/length = 0.0400 kg/m is suspended as shown in the figure. What current will produce zero tension in the supporting wires if B = 3.60 T? PSE6 29.p.14
A. 57.3 mA
B. 109 mA
C. 525 mA
D. 1.77 A
Answer























POP4 q22.10
Picture (195x208, 1.3Kb) Two perpendicular wires are almost touching and carrying currents in the manner shown. What is the force between the wires?
A. strong and attractive
B. strong and repulsive
C. weak and attractive
D. zero
Answer















PSE6 29.22
Ten windings of wire are formed into a square of side length 0.100 m. The coil is hinged along a horizontal side, carries a 3.40-A current, and is placed in a vertical magnetic field of magnitude 0.0100 T. Determine the angle that the plane of the coil makes with the vertical when the coil is in equilibrium. Figure for PSE6 problem 29.22
A. 4.0°
B. 12°
C. 21°
D. 29°
Answer















Walker5e CnEx 22-12
When the switch is closed the wire between the poles of the horseshoe magnet deflects downward. Is the left end of the magnet a north magnetic pole or a south magnetic pole?


A. north
B. south
C. either pole produces a downward deflection
Answer















Walker5e 22.64
Four wires each carry current I in the directions shown. What is the direction of the magnetic force experienced by wire 2?

(Select the direction indicated by the letters)


Answer



























 



A. gravity < electric < magnetic






















 



D. 65.6 mT






















 



B. 27.0 µN left




























 



B. 109 mA

solution equation
You can also suspend a live frog in a magnetic field! However, the physics of how this happens is a little different than the force on an electric current.















 
D. zero
The magnetic field from one wire is everywhere parallel to the current in the other wire. Therefore, the magnetic force per length I × B is zero.




















 
Figure for PSE6 problem 29.22
A. 4.0°
solution equation





















 



A. north
Using the right-hand-rule, if your thumb points downward (the direction of the force) your fingers curl toward the right (the direction of the magnetic field). Magnetic fields come out of the north pole and enter the south pole of a magnet.





















 



Direction f
Wire 2 will be attracted by wires 1 and 3 but repelled by wire 4. The repulsive force from wire 4 will be smaller than the other two forces because wire 4 is farther away. Adding the vectors head-to-tail reveals a net force toward wire 4, or in the direction indicated by "f".















The photo above depicts aurora loops around the southern polar region in the distance as viewed by astronauts onboard the space shuttle Discovery on STS-39 in 1991. 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. Source: NASA Image Exchange


aurora from space
Red and green colors predominate in this view of the Aurora Australis photographed from the Space Shuttle in May 1991 at the peak of a geomagnetic maximum. Source: NASA Earth Observatory


More auroras from space
Here is another photograph of the southern lights taken by astronauts onboard the Space Shuttle Discovery. The emissions, extending nearly vertically upward, 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.


ISS aurora photo
Here is an even better photo from the International Space Station (See a movie!)


Of course, auroras are also visible from earth!


aurora in Norway
Aurora photographed by Markus Varik on February 19, 2018 in Tromsø, Norway. From the spaceweather.com real-time aurora gallery


aurora in Maine
Aurora photographed by Mark Taylor on September 12, 2014 in central Maine. From phys.org/news/2015-01-northern.html