Unit 4 Day 7: Magnetic Fields due to Wires Magnetic Field in a Straight Wire Magnetic Fields in 2 Parallel Conducting Wires, Side by Side Magnetic Forces.
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Unit 4 Day 7: Magnetic Fields due to Wires
• Magnetic Field in a Straight Wire
• Magnetic Fields in 2 Parallel Conducting Wires, Side by Side
• Magnetic Forces Between Parallel Wires
Magnetic Field in a Straight Wire• In a straight, current carrying conductor,
there exists a magnetic field around the wire, proportional to the current
r is the radial distance from the conductor
AmTwhere
r
IB
70
0
104
2
Two Current Carrying Conductors Side by Side
• If there are two current carrying conductors side by side, but the current is going in the opposite directions, then the total magnetic field will have a magnitude of:
21 BBBTotal
Magnetic Force Between Parallel Wires• We know that when a current carrying conductor is in the
presence of a magnetic field, it feels a force exerted by that field.
Magnetic Force Between Parallel Wires• The force that wire #2 sees is due to the
magnetic field generated by wire #1, separated by distance d
• Similarly, wire #1 sees a force due to the magnetic field of wire #2 (Newton’s 3rd Law)
d
lIIF
d
IBbut
BlIF
2
2
22102
101
1222
d
lIIF
2
12101
Magnetic Forces Between Parallel Wires
• Parallel currents in the same direction exert an attractive magnetic force on each other
• Parallel currents in the opposite direction exert a repulsive force on each other
• It can be shown from Newton’s 3rd Law, that the magnetic force produced by I2 exerts an equal but opposite force on I1
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