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4.1 Why were Tesla's AC patents so important for the widespread acceptance of AC?
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A: They provided the means to build an AC induction motor, which, until Tesla's work, was unavailable and thus AC was not as useful as DC. (also) They provided the means for creating a centralized AC power generation model as opposed to a distributed DC model. |
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4.2 What intrinsic property of atoms produces a magnetic field with a given strength and orientation?
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4.3 If everything is made up of atoms, all atoms have electrons, and all electrons have a magnetic dipole, why are some materials more magnetic than others?
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| A: Because they are randomly aligned in most materials and the magnetic fields cancel. |
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4.4 True or false: In some materials, unpaired electrons spontaneously align themselves and reinforce their magnetic fields.
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4.5 True or false: The flow of current always produces a magnetic field.
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4.6 The right hand rule is an aid for visualizing the _________ of _________ of a magnetic field around a current carrying conductor.
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4.7 A stationary magnetic field does not induce current in a coil of wire, but a _________ one does.
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4.8 What is Faraday's law of induction?
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| A: The voltage in a loop of wire is proportional to the rate of change of a magnetic field through the wire. |
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4.9 A wire traveling _________ to the lines of flux in a magnetic filed field produces no voltage. A wire traveling _________ to the lines of flux in a magnetic field produces maximum voltage.
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| A: Parallel, perpendicular |
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4.11 True or false: A conductor moving at a right angle to a magnetic field at a speed of 2x inches per second will generate twice the voltage as a conductor moving at a right angle to the same magnetic field at a speed of x inches per second.
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4.12 True or false: Fleming's right-hand rule indicates the direction of the force applied to a conductor moving through a magnetic field in a motor.
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| A: False, it indicates the direction of the force applied to a conductor moving through a magnetic field in a generator. |
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4.13 What is the sine of 320 degrees rounded to the nearest thousandth? 270 degrees?
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4.14 Why are both the sine of zero and the sine of 360 degrees equal to 0?
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A: Because they are both the same point on the circle.
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4.15 If the angle between the direction of travel off a spinning rotor and a magnetic field is 20 degrees and the peak voltage is 169.7 volts, what is the instantaneous voltage?
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| A: V instantaneous =V peak x sin0 =169.7 x sin20degrees = 58.04 volts |
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4.16 What is the voltage of a sinewave at a phase angle of 160 degrees if the peak voltage is 100
volts?
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4.17 How fast does a generator have to spin in order to produce a 60-Hz frequency if it has 16 poles?
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A: Speed of rotation (RPM) x number of poles = 120 x frequency (Hz)
Speed of rotation = (120x60)/16 = 450 RPM
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4.18 If the frequency of a sinewave is 50Hz, how long does it take to complete one cycle.
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4.19 What is the rotational speed of an eight-pole generator supplying power at 50 Hz?
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A: Speed of rotation (RPM) x number of poles = 120 x frequency (Hz)
Speed of rotation = (120x50)/8 = 750 RPM
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4.21 What is the frequency of the mains power in Europe? North America?
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4.23 If the RMS voltage in Europe is 230 V, what is the peak voltage?
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