S13Phys2BaLec31A

# So if we were to look in the direction of the

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So, if we were to look in the direction of the magnetic field, we would observe a counterclockwise current.

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Rotating Loop Next, suppose the loop is rotating in a uniform magnetic field such that its magnetic flux is decreasing at that particular moment. What will be the direction of the induced current in the top section of the loop? By Lenz’s Law, the direction of the induced current will be into the board as it tries to oppose the decreasing magnetic flux. So, if we were to look in the direction of the magnetic field, we would observe a clockwise current.
AC Current This is the basis of alternating current. As the rotating loop goes through one entire rotation half the time it will have current moving one direction (ccw) and half the time it will have current moving the other direction (cw). The current alternates direction as it goes through a single rotation. In a stationary magnetic field, some of the time the magnetic flux increases and some of the time it decreases.

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AC Current The induced emf generated by the rotating loop can be found by: If the rotating loop with a constant angular speed, ω , and has N turns: ε = 2 B v = 2 B v sin θ ε = NBA ω sin ω t When loop is parallel to field, emf is maximum. When loop is perpendicular to field, emf is zero. ! = ! N d " B dt
s rad AC Generator emf [T] [V] I (ccw/cw) = [m 2 ] RHR ε ( t ) = ω NBA sin( ω t ) B rot. coil B

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LC Circuits A good way to view AC current is with the simple case of the LC circuit (note there is no resistor or battery in this circuit). A switch closes at a time t = 0.
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