1. 22.3 Inductance pp. 814 - 819 Mr. Richter

2. Agenda  Warm Up  Notes:  Mutual Inductance  Transformers

3. Objectives: We Will Be Able To…  Describe how mutual induction occurs in circuits.  Calculate the potential difference from a step-up or step- down transformer.

4. Warm-Up:  Transformers are used to “step down” the voltage from power lines, about 100,000 V to the 120 V household levels. If the voltage decreases, what must increase as a result?

5. Mutual Inductance

6.  If a coil with current running through it is wrapped around an iron core, a magnetic field is generated.  If a second coil is wrapped around the core, current is induced in the second coil.  This process transferring the current of one circuit to a nearby circuit is called mutual inductance.

7. Mutual Inductance  If the number of turns of the wire (N 1 ) of the primary coil is different from the number of turn of the secondary coil (N 2 ), the amount of current flowing in each circuit will change.  As a result, the voltage in the second circuit will be different than the voltage in the first.

8. Transformers

9.  A transformer is a device that changes one potential difference to a different potential difference.  If the number of coils in the secondary coil is more than the primary, the voltage is increased.  This is called a “step-up” transformer.  A “step-down” transformer does the opposite. Voltage decreases.

10. Transformers  The voltage change in a transformer is directly proportional to the ratio of the number of turns of the wire in the coil.  If the voltage increases, the current flowing through the secondary coil decreases, and vice versa.  Power through both circuits stays the same.

11. Transformers  A step-up transformer is used on a 120 V line to proved a difference of 2400 V. If the primary coil has 75 turns, how many turns must the secondary coil have?  N 2 = 1500 turns

12. Wrap-Up: Did we meet our objectives?  Describe how mutual induction occurs in circuits.  Calculate the potential difference from a step-up or step- down transformer.

13. Homework  p. 823 #29-31, 35, 36