1. TRANSFORMERS?

2. Effects of electric current An electric current that flows in a conductor has a number of effects: 1. HEATING The friction caused by the current causes the conductor to heat up. The greater the current the more heat is generated. 2. MAGNETIC EFFECT - A magnetic field is generated around any conductor when an electric current flows through it.

3. Magnetic Effect A magnetic field is generated around any conductor when an electric current flows through it. Electric current Wire with current coming towards you Wire with current going away from you x

4. SOLENOID A coil generates a very concentrated (strong) magnetic field in its center. Electric current x N S xx Increasing the number of coils strengthens the magnetic field. The Right Hand Rule can also be applied to a solenoid! INSIDE THE COIL THE FIELD GOES FROM SOUTH TO NORTH!!!

5. Mutual Induction MUTUAL INDUCTION is defined as the changing electric …………………… producing a changing …………………….. field which can produce a changing ………………….. in another conductor. This is the basic principle of the ……………………… ~

6. Mutual Induction MUTUAL INDUCTION is defined as the changing electric current producing a changing magnetic field which can produce a changing current in another conductor. TRANSFORMER This is the basic principle of the TRANSFORMER ~ 1. Changing electric current 2. Changing magnetic field 3. Changing (INDUCED) electric current

7. Transformers Coils of insulated conducting wire are wound around a ring of iron constructed of thin isolated laminations or sheets. The laminations minimize eddy currents in the iron. Eddy currents are circulatory currents induced in the metal by the changing magnetic field. These currents produce an undesirable by-product—heat in the iron. Energy loss in a transformer can be reduced by using thinner laminations, very “soft” (low-carbon) iron and wire with a larger cross section, or by winding the primary and secondary circuits with conductors that have very low resistance. Transformers used to transmit and distribute power are commonly 98 to 99 percent efficient. While eddy currents are a problem in transformers, they are useful for heating objects in a vacuum.

8. Ideally – all magnetic flux from primary coil links with secondary coil. The number of turns of wire is directly proportional to the voltage in the coil. Transformers NpVpNsVsNpVpNsVs — = — How many turns of wire would you need in a transformer that has 1000 turns in the primary and needs to step down the voltage from 220V to 9V? vpVSNPNsvpVSNPNs — = —

9. Ideally – all magnetic flux from primary coil links with secondary coil. The number of turns of wire is directly proportional to the voltage in the coil. Transformers NpVpNsVsNpVpNsVs — = — How many turns of wire would you need in a transformer that has 1000 turns in the primary and needs to step down the voltage from 220V to 9V? Vp=Vs NpNs 220=9 1000Ns =40.9turns

10. From Faraday’s Law: “The size of the induced current is directly proportional to the rate of change of the magnetic flux linkage.” Therefore: work done by primary = energy gained by secondary Transformers Since W = QV and Q = It.: W = VIt W p = W s......... =...................... =...................... =........... Calculate the current in the secondary coil of the 220V/9V transformer if the current in the primary was 1.5A

11. From Faraday’s Law: “The size of the induced current is directly proportional to the rate of change of the magnetic flux linkage.” Therefore: work done by primary = energy gained by secondary Transformers Since W = QV and Q = It.: W = VIt W p = W s V p I p t = V s I s t V p I p = V s I s P p = P s Calculate the current in the secondary coil of the 220V/9V transformer if the current in the primary was 1.5A