Unit 14Magnetic Induction

Unit 14 Magnetic Induction

Objectives:

• Discuss magnetic induction.

• List factors that determine the amount and polarity of an induced voltage.

• Discuss Lenz’s law.

• Review the formula for R-L time constants.

Unit 14 Magnetic Induction

Current flowing through a conductor produces a magnetic field around the conductor.

Current flowing out Current flowing in

Unit 14 Magnetic Induction

A voltage is induced when a conductor cuts magnetic lines

of flux.

Unit 14 Magnetic Induction

Reversing the direction of movement reverses the polarity of the voltage.

Unit 14 Magnetic Induction

Reversing the polarity of the magnetic field reverses the polarity of the voltage.

Unit 14 Magnetic Induction

Left-hand generator rule.

Unit 14 Magnetic Induction

Voltage is induced by a moving magnetic field.

Unit 14 Magnetic Induction

A single-loop generator.

Unit 14 Magnetic Induction

Increasing the number of turns increases the induced voltage.

Unit 14 Magnetic Induction

Lenz’s LawAn induced voltage or current opposes the

motion that causes it.

Please note:Inductors always oppose a change of current!

Unit 14 Magnetic Induction

Inductance is determined by the physical construction of the coil.

Unit 14 Magnetic Induction

R-L Time ConstantsT = L / R

T = time in secondsL = inductance in henrysR = resistance in ohms

This formula describes the time necessary for current in an inductor to reach its full Ohm’s law value.

Unit 14 Magnetic InductionReview:

1. When current flows, a magnetic field is created around the conductor.

2. When a conductor is cut by a magnetic field, a voltage is induced in the conductor.

3. The polarity of the induced voltage is determined by the polarity of the magnetic field.

Unit 14 Magnetic Induction

Review:

4. Three factors that determine the amount of induced voltage are:

a. the number of turns of wire.b. the strength of the magnetic field.c. the speed of the magnetic flux cutting

action.

Unit 14 Magnetic Induction

Review:

5. Induced voltage is always opposite in polarity to the applied voltage.

6. Inductors oppose a change of current.7. Inductance is measured in units called

henrys (H).8. Iron core inductors are wound on cores

of magnetic material.