1. IB Physics 12
Mr. Jean
December 15th, 2014

3. 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.

4. 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

6. 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.

8. 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.

9. 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.

10. Transformers:
Transformers are used to transfer energy from one circuit to another by means of mutual inductance between two coils.

11. 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)

12. 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).

13. 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

15. Transformers: Brightstorm: Transformers

16. Sample Questions:
At the Equator near Earth’s surface, the magnetic field is approximately 50.0 μT northward and the electric field is about 100 N/C downward in fair weather.
Find the gravitational, electric, and magnetic forces on an electron with an instantaneous velocity of 6.00x106 m/s directed to the east in this environment.

17. Find the Gravitational Force

18. Find the electric force

19. Find the magnetic forces

20. Traveling Through a field:
A proton travels with a speed of 3.0x106 m/s at an angle of 37° with the direction of a magnetic field of 0.30 T in the +y direction.
What are (a) the magnitude of the magnetic force on the proton?
(b) the proton’s acceleration?

22. Example:
Sodium ions (Na+) move at m/s through a bloodstream in the arm of a person standing near a large magnet. The magnetic field has a strength of T and makes an angle of 51.0° with the motion of the sodium ions. The arm contains 100 cm3 of blood with 3.00x1020 Na+ ions per cubic centimeter. If no other ions were present in the arm, what would be the magnetic force on the arm?

26. Example:
A current I = 15 A is directed along the positive x axis and perpendicularly to a magnetic field. The conductor experiences a magnetic force per unit length of 0.12 N/m in the negative y direction. Calculate the magnitude and direction of the magnetic field in the region through which the current passes.

29. Example:
A single-turn square loop of wire, 2.00 cm on a side, carries a counterclockwise current of A. The loop is inside a solenoid, with the plane of the loop perpendicular to the magnetic field of the solenoid. The solenoid has 30 turns per centimeter and carries a counterclockwise current of 15.0 A.
Find the force on each side of the loop and the torque acting on it.