Transcript Chapter 20
Electromagnetic Induction Chapter 20 Section 1 Section 1 Electricity from Magnetism © Houghton Mifflin Harcourt Publishing Company Section 1 Electromagnetic Induction Section 1 What do you think? • The loop of wire is rotating in a counterclockwise direction. • Electrons in metal are free to move. • The magnetic field is horizontal and to the left. See the next slide for questions. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 What do you think? • • © Houghton Mifflin Harcourt Publishing Company Will there be a force on the electrons in the left and right segments of the loop? – If so, in what direction is that force? In which direction will the electrons flow if the two wires from the ends are connected? Electromagnetic Induction Section 1 Electromagnetic Induction • Imagine a wire moving to the right as shown. – In what direction is the force on the negative charge? • Upward – This force will separate the charges. – As negative charges move upward, the wire will develop a potential difference. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Electromagnetic Induction • Electromagnetic induction is the process of creating a current in a circuit loop by changing the magnetic flux in the loop. – This can be accomplished by moving the loop, moving the field, or changing the strength of the field. • If the magnetic flux does not change, no current is induced. • The current is increased if the loop size or magnetic field strength are increased. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Ways of Inducing a Current in a Circuit Click below to watch the Visual Concept. Visual Concept © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Lenz’s Law • As the magnet enters the coil, a force pushes the electrons around the loop, inducing a current. • The induced current creates a magnetic field that opposes the motion of the magnet. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Lenz’s Law • Now the magnet is being removed from the coil as it moves to the right. • This induces a current in the opposite direction. • Once again, the magnetic field in the coil opposes the motion of the magnet. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Lenz’s Law • The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it. • This rule can be used to find the direction of the current in the loop. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Lenz's Law for Determining the Direction of the Induced Current Click below to watch the Visual Concept. Visual Concept © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Faraday’s Law • The magnitude of the induced emf depends on the number of loops (N), the magnetic flux (M), and the rate of change. • M = AB cos © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Classroom Practice Problem • A coil with 25 turns of wire is moving in a uniform magnetic field of 1.5 T. The magnetic field is perpendicular to the plane of the coil. The crosssectional area of the coil is 0.80 m2. The coil exits the field in 1.0 s. – Find the induced emf. – Determine the induced current in the coil if the coil’s resistance is 1.5 . • Answers: – 3.0 101 V, 2.0 101 A © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Now what do you think? • The loop of wire is rotating in a counterclockwise direction. • Electrons in metal are free to move. • The magnetic field is horizontal and to the left. • The ends of the coil are connected to a load such as a light bulb (not shown). See the next slide for questions. © Houghton Mifflin Harcourt Publishing Company Electromagnetic Induction Section 1 Now what do you think? • • • • © Houghton Mifflin Harcourt Publishing Company In which direction will the electrons flow around the loop? What is the direction of current in the loop? Use the right-hand rule to find the magnetic field created by the current in the loop. Does this magnetic field oppose the motion of the loop?