# lecture13a - ConcepTest 20.8a Magnetic Field of a Wire I...

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Unformatted text preview: ConcepTest 20.8a Magnetic Field of a Wire I Magnetic 1) direction 1 If the currents in these wires have 2) direction 2 the same magnitude, but opposite 3) direction 3 directions, what is the direction of 4) direction 4 the magnetic field at point P? 5) the B field is zero 5) 1 P 4 2 3 ConcepTest 20.8a Magnetic Field of a Wire I ConcepTest Magnetic If the currents in these wires have the same magnitude, but opposite directions, what is the direction of the magnetic field at point P? 1) direction 1 2) direction 2 3) direction 3 4) direction 4 5) the B field is zero 5) 1 P Using the right-hand rule, we can sketch the B fields due to the two currents. Adding them up as vectors gives a them total magnetic field pointing downward. downward 4 2 3 ConcepTest 20.8b Magnetic Field of a Wire II ConcepTest Magnetic Each of the wires in the figures below carry the same current, either into or out of the page. In which case is the magnetic field at the center of the square greatest? 1 B=? 2 B=? 1) arrangement 1 2) arrangement 2 3) arrangement 3 4) same for all 3 B=? ConcepTest 20.8b Magnetic Field of a Wire II ConcepTest Magnetic Each of the wires in the figures below carry the same current, either into or out of the page. In which case is the magnetic field at the center of the square greatest? 1 2 1) arrangement 1 2) arrangement 2 3) arrangement 3 4) same for all 3 ConcepTest 20.9a Field and Force I Field 1) + z (out of page) A positive charge moves parallel positive to a wire. If a current is suddenly turned on, which direction will the 2) - z (into page) 2) 3) + x 3) 4) - x 4) force act? force 5) - y 5) y +q x z I ConcepTest 20.9a Field and Force I ConcepTest Field A positive charge moves parallel positive to a wire. If a current is suddenly turned on, which direction will the force act? force 1) + z (out of page) 2) - z (into page) 2) 3) + x 3) 4) - x 4) 5) - y 5) Using the right-hand rule to determine the magnetic field produced by the wire, we find that at the position of the charge + q (to the left of the wire) the B field points out of the page. Applying the right-hand out rule again for the magnetic force on the charge, we find that +q experiences a force in the +x direction. +x y +q x z I ConcepTest 20.9b Field and Force II ConcepTest Field Two straight wires run parallel to each other, each carrying a current in the direction shown below. The two wires experience a force in which direction? force 1) toward each other 2) away from each other 3) there is no force ConcepTest 20.9b Field and Force II ConcepTest Field Two straight wires run parallel to Two each other, each carrying a current in the direction shown below. The two wires experience a force in which direction? force 1) toward each other 2) away from each other 3) there is no force The current in each wire produces a magnetic field that is felt by the current of the other wire. Using the right-hand rule, we find that each wire experiences a force toward the other wire (i.e., an attractive force) when the attractive currents are parallel (as shown). currents Follow-up: What happens when one of the currents is turned off? one ConcepTest 20.10 Current Loop Current 1) left What is the direction of the What 2) right magnetic field at the center 3) zero (point P) of the square loop 4) into the page of current? of 5) out of the page I P ConcepTest 20.10 Current Loop ConcepTest Current What is the direction of the What magnetic field at the center (point P) of the square loop of current? of Use the right-hand rule for each wire segment to find that each segment has its B field pointing out of the page at point P. out 1) left 2) right 3) zero 4) into the page 5) out of the page I P ...
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