Section 2 review
Electric current can be created by a process called electromagnetic induction—by changing the magnetic flux through a conducting loop. The flux is the product of the loop’s area, magnetic field strength, and orientation of the loop relative to the field. Faraday’s law of induction tells us how much voltage will be generated. A generator uses induction to change mechanical work into electrical energy. A transformer uses the changing magnetic flux caused by changing voltage in one wire to induce a changing voltage in another wire. Read the text aloud
magnetic flux, Faraday’s law of induction, electromagnetic induction, Lenz’s law, electrical generator, transformer

Φ B =BAcosθ
emf=N Δ Φ B Δt
V s V p = N s N p

Review problems and questions

Diagram representing a simple electrical generator
  1. The figure represents a simple electrical generator. Mechanical forces (such as wind) cause a wire coil to rotate in the presence of a magnetic field. Suppose that the rotation rate is beyond your control but that you can modify the properties of the generator itself. List three ways you could increase the voltage it produces. Read the text aloud Show
  1. George’s electrical toy requires two 1.5 V AA cells (in series, for a total of 3 V). He only has one AA cell, but he has a transformer with a 2:1 turn ratio. Can he use his toy? Read the text aloud Show
What is the direction of the induced electric current?
  1. Marcia inserts the N pole of a bar magnet into the right side of a wire coil and induces a temporary positive current. Would she induce (+) or (−) current if she
    1. inserted the S pole into the right side of the coil?
    2. inserted the N pole into the left side of the coil?
    3. inserted the S end into the left side? Read the text aloud Show
Loop of wire turning in a magnetic field
  1. A loop of wire rests at right angles to a uniform, upward-pointing magnetic field. The loop is 20 cm wide and 60 cm long. The coil begins to turn and then stops after rotating 90°. The magnetic field has a strength of 0.1 T. What is the magnetic flux through the loop in each of the states shown here? Read the text aloud Show

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