102lect11_handout

102lect11_handout - Physics 102: Lecture 11 Generators and...

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Physics 102: Lecture 11, Slide 1 Generators and Transformers Physics 102: Lecture 11
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Physics 102: Lecture 11, Slide 2 Review: Induction • Faraday’s Law – Magnitude of induced EMF given by: • Lenz’s Law – If magnetic flux ( Φ ) through loop changes, an EMF is created in the loop to oppose the change in flux – EMF current (V=IR) induced B-field. • Flux decreasing => B-field in same direction as original • Flux increasing => B-field in opposite direction of original f i ݂ ݅
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Physics 102: Lecture 11, Slide 3 Review: Magnetic Flux φ is angle between normal and B Φ = B A cos( φ) Units are T m 2 = Wb B φ 3 things can change Φ: 1. Area of loop 2. Magnetic field B 3. Angle φ between normal and B Last lecture Today
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Physics 102: Lecture 11, Slide 4 • Changing current • Changing B sol field • Changing Φ through itself! Φ proportional to I: Self-Inductance • Induced EMF (voltage) – Recall Faraday’s law: • Direction – Given by Lenz’s Law – Opposes change in current! Units: L = ε t / I 1 H = 1V-sec/amp B sol B ind Recall from last time the solenoid cannon “Inductance” ߝൌെ ∆Φ Δݐ ൌെܮ ∆ܫ Δݐ ൌെܮ ܫ ݂ െܫ ݅ ݐ ݂ െݐ ݅
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Physics 102: Lecture 11, Slide 5 Inductor resists current change! Recall: Φ = NBA Recall: B = μ o nI (# turns) = (# turns/meter) x (# meters) N = n l Energy stored: U = ½ LI 2 Physical Inductor A N 0 0 0 2 l
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Physics 102: Lecture 11, Slide 6 a b c d B B φ normal φ normal Generators and EMF A loop of wire is rotated (ex: by a steam engine turbine) in a uniform B field Φ = B A cos( φ) Loop normal rotates relative to B field => φ changes => Φ changes => emf in loop => voltage generated!
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Physics 102: Lecture 11, Slide 7 Review (Phys 101): Rotation
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102lect11_handout - Physics 102: Lecture 11 Generators and...

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