IB Physics 12 Mr. Jean December 9 th , 2013
Apr 01, 2015
IB Physics 12
Mr. Jean
December 9th, 2013
The plan:
• Video clip of the day
• AC Motors
• DC & AC generators
• Transformers
AC Electric Motor
• Uses slip rings as commulator.
• Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave.
• The magnetic field is sinusoidally varying, just as the current in the coil varies.
AC vs. DC Motors:
• Electric motors are mostly AC because our electric energy for industry and home is transmitted as AC.
• DC motor – starter motor on a car.
AC Electric Motor
• Uses slip rings as commulator.
• Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave.
• The magnetic field is sinusoidally varying, just as the current in the coil varies.
AC vs. DC Motors:
• Electric motors are mostly AC because our electric energy for industry and home is transmitted as AC.
• DC motor – starter motor on a car.
AC Generators:
• Generators are essentially the same design as motors. – The mechanical energy input to a generator turns the
coil in the magnetic field. This produces an emf (voltage). A sinusoidal voltage output.
• The mechanical energy may come from:– i. Steam– ii. Wind– iii. Waterfall– iv. Electric motor
DC Generator: • The commutator must change the AC
flowing into its armature into DC.
• Commutators keep the current flowing in one direction instead of back and forth.
Power Production
• Generators were built by Tesla to generate electricity reliably and in large quantities.
• Most of today’s energy sold is in the form of AC because it can easily be transformed from one voltage to another.
High Voltage with Low Current:
• Power is transmitted at high voltages and low current without much energy loss (heating of wire) because it can be stepped down from the plant to many cities, to a city, to the household.
• Household typical outlet is 120 V AC.
Transformers: • Transformers are used to transfer energy
from one circuit to another by means of mutual inductance between two coils.
Types of Transformers:
• Transformers consist of a primary coil (input) and a secondary coil (output).
• Step-up Transformer – Secondary has more turns – greater electric potential (V) induced, caused
by the lowering for current (I)
Types of Transformers:
• Transformers consist of a primary coil (input) and a secondary coil (output).
• Step-down Transformer – primary has more turns– Thus less electric potential (V) induced
causing a greater current (I).
Transformers:
• Transferring energy from one coil to the other OR the rate of transferring energy is the power.
• The power used in the secondary is supplied by the primary.
• LAW OF CONSERVATION OF ENERGY
Transformers:
• Brightstorm: Transformers– http://www.youtube.com/watch?v=4aYhAbzS
wvs