Physics 12

Mr. JeanMay 6th, 2014

The plan:

• Video clip of the day• AC/DC power generation• AC/DC electric engines

DC Electric Motor• Has a coil with an iron core ARMATURE• It is surrounded by electromagnets

Problems with DC Power:

• 1. The magnetic forces are aligned directly opposite each other and will no longer experience a torque.– If you could change the direction of the current,

the coil would again experience a torque.• 2. If the coil keeps turning, the leads will twist

and eventually break.

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 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.

Introduction to DC Power & Motors:

• http://www.youtube.com/watch?v=OpL0joqJmqY

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=4aYhAbzSwvs