TRANSFORMERS?

1. TRANSFORMERS?

2. Effects of electric current An electric current that flows in a conductor has a number of effects: • HEATING The friction caused by the current causes the conductor to heat up. The greater the current the more heat is generated. • 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 x x A coil generates a very concentrated (strong) magnetic field in its center. Increasing the number of coils strengthens the magnetic field. The Right Hand Rule can also be applied to a solenoid! Electric current N x S 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. • This is the basic principle of the TRANSFORMER 2. Changing magnetic field 1. Changing electric current ~ 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. Transformers Np Vp Ns Vs vpVS NPNs — = — — = — • 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. 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?

9. Transformers NpVp Ns Vs — = — • 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. 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?

10. Transformers 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 Since W = QV and Q = It .: W = VIt Wp = Ws ......... = ........... ........... = ............. ......... = ........... Calculate the current in the secondary coil of the 220V/9V transformer if the current in the primary was 1.5A

11. Transformers 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 Since W = QV and Q = It .: W = VIt Wp = Ws VpIpt = VsIst VpIp = VsIs Pp = Ps Calculate the current in the secondary coil of the 220V/9V transformer if the current in the primary was 1.5A