Electromagnetic Induction Chapter 29 Electromagnetic Induction

To consider Faraday’s Law To consider Lenz’s Law To study motional emf Goals for Chapter 29 To consider Faraday’s Law To consider Lenz’s Law To study motional emf To explore induced electric fields To summarize Maxwell’s equations and see their application to displacement current

Introduction The motion of a magnet can induce current in practical ways. If a credit card has a magnet strip on its back, “swiping” the card can generate tiny currents that send information to cash registers. A coil of wire and magnets set into motion around each other will generate currents in the wire. A source of mechanical energy can drive the rotation and make a waterfall into an electrical power station.

Induced current Joseph Henry worked in the United States and Michael Faraday worked in England to discern the details of current generated in wire and permanent magnets in motion relative to each other. See Figure 29.1 below.

Knowing the magnetic flux Regardless of what moves, knowing the magnetic flux around a conducting entity will allow determination of current induced. See Figure 29.3 at right and Figure 29.4 below.

Emf and the current induced in a loop Follow Example 29.1. Figure 29.5 illustrates the example.

Find the direction of an induced emf Consult Figure 29.6 and the text on the bottom of page 997 and top of page 998 and solve.

Faraday’s Law Follow Problem-Solving Strategy 29.1. Refer to Example 29.2. Figure 29.7 illustrates Example 29.2.

The search coil, generator example I Follow Conceptual Example 29.3. Consider Example 29.4 and Figures 29.8 and 29.9.

Generator example II The example considers a DC generator and back emf in a motor.

Generator example III Follow Example 29.6. Figure 29.11 illustrates Example 29.6.

Work and power in a slidewire generator Follow Example 29.7. Figure 29.12 illustrates Example 29.7.

Lenz’s Law The direction of any magnetic induction effect is such as to oppose the cause of the effect. Follow Conceptual Example 29.8. Follow Example 29.9; Figure 29.14 illustrates the example.

A conducting rod moving in a uniform magnetic field The rod, velocity, and current are mutually perpendicular. See the direction of the induced current in the circuit below. Follow Example 29.10.

The Faraday Disk dynamo Follow Example 29.11. Figure 29.16 illustrates Example 29.11.

Induced electric fields I The windings of a long solenoid carrying a current I

Induced electric fields II Refer to Figure 29.18 below. Follow Example 29.12.

Eddy currents Consider Figure 29.19 at right. Consider Figure 29.20 below.

Displacement current and Maxwell’s equations A varying electric field will give rise to a magnetic field. Explains electromagnetic waves.

Superconductivity and the Meissner effect When cooled below the critical temperature, superconductive materials lose all resistance to electrical current. Refer to Figures 29.24 and 29.25 at right.