lecture 16

lecture 16 - 22.7 Generators So running a current thru a...

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22.7 Generators So running a current thru a loop of wire in a magnetic field causes it to rotate. The reverse of this process is also true Rotate a conducting loop in a magnetic field, and a current is produced (motional emf). The motional emf , was derived for v being perpendicular to B . vBL = ε But, as the loop rotates, the angle between v and B changes. hus the true motional mf a Thus, the true motional emf is a function of angle: θ sin vBL = Since the loop’s motion is rotational, it is convenient to express v and in rms of angular variables: terms of angular variables: ω r v = t θ=
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If we let A be the area of the loop and N the number of turns in the loop, then we find the following expression for the emf produced by the loop: t NAB ω ε sin = is useful to write it this way: It is useful to write it this way: t o sin = , where NAB Max o = = emember that as the units of [ d ], and = w h e r e in [Hz]. Remember that has the units of [rad/s], and f π 2 , where f is in [Hz]. The emf produced by the coil is a sinusoidal function, and therefore changes sign as a function of time. g ) ( t o + otice: The mf *Notice: The emf oscillates between its positive and t o negative maximum value.
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Since the emf changes sign as a function of time, so does the current, I : This is an example of an AC (Alternating Current) Generator .
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22.5 Lenz’s Law ΔΦ s A Remember Faraday’s Law: t N M Δ = ε , where . cos φ BA M = Φ So a changing magnetic field can produce a current.
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This note was uploaded on 08/04/2009 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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lecture 16 - 22.7 Generators So running a current thru a...

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