A motor converts ______________energy into __________energy. A motor converts ______________energy into __________energy.

Induced Voltage:Three Cases The B Field can change : V= NA(  B /  t ) The area can change (motional emf):  V= BLv The angle can change (generator):   V =  NBA sin  t

The B Field can change : V= NA(  B /  t ) The B Field can change : V= NA(  B /  t ) Example: A magnet is moved into a coil with 100 turns and an area.10m 2. The field in the loop changes from zero to 2T in.1 seconds. 1. What is the induced voltage? V = NA(  B /  t ) = (100)(.1)( 2/.1) = 200Volts 2. If the coil has a resistance of 100 Ohms, what’s the current in the coil? I = V/R = 200/100= 2 Amps

The area can change:  V= Blv Example: A metal bar moves to the right with a velocity of 10m/s through a magnetic field of 3T. The loop height, L, is.5m. 1. What is the induced voltage? 2. If the circuit has a resistance of 2 Ohms, what’s the current in the circuit? V = BLv = (3)(.5)( 10) = 15Volts I = V/R = 15/2= 7.5 Amps

The angle can change:  V=  NBA sin  t The angle can change:  V=  NBA sin  t Example: A generator turns at 100rad/sec. It has 500 turns, and a magnetic field of.5T. The loop area is.01 m 2. What is the maximum voltage? This is used for the generator. The maximum voltage is: V max =  NBA. This is used for the generator. The maximum voltage is: V max =  NBA. V max =  NBA = 100(500)(.5)(.01) = 250Volts.

When an external magnetic field changes through a conducting loop, a current is induced that produces another magnetic field that opposes the external change.

As the magnet moves, the current in the resistor goes from…. A to B

As the magnet moves, the current in the resistor goes from…. B to A

If the B field points out and increases, the current in the loop is………….. Clockwise

If the B field points in and increases, the current in the loop is………….. Counter - Clockwise

If the B field points into this conducting loop of wire and increases with time, the direction of the current in the loop is………….. Counter-Clockwise

Transformers

Transformer Equations N 1 = number of turns on the primary side N 2 = number of turns on the secondary side V 1 = AC voltage applied to the primary side V 2 = AC voltage on the secondary side I 1 =current in the primary windings I 2 = current in the secondary windings

From Faraday’s Law : V 2 = V 1 (N 2 /N 1 ) From conservation of energy: V 1 I 1 = V 2 I 2 Then: I 2 = I 1 (N 1 /N 2 ) From Faraday’s Law : V 2 = V 1 (N 2 /N 1 ) From conservation of energy: V 1 I 1 = V 2 I 2 Then: I 2 = I 1 (N 1 /N 2 ) Transformer Equations

Step Up Transformer N 2 >N 1 Example: A transformer has 5000 turns in the secondary and 1000 turns in the primary. The primary voltage is 100V (AC) and the primary current is 25 Amps. 1. What is the secondary voltage? 2. What is the secondary current? 3. What is the power in the primary and secondary? Example: A transformer has 5000 turns in the secondary and 1000 turns in the primary. The primary voltage is 100V (AC) and the primary current is 25 Amps. 1. What is the secondary voltage? 2. What is the secondary current? 3. What is the power in the primary and secondary?

Solve the Problem Givens: V 1 = 100 N 1 = 1000 N 2 = 5000 I 1 = Solve for V 2 : V 2 = V 1 (N 2 /N 1 ) = 100( 5000/1000) = 500 Volts 2. Solve for I 2 : I 2 = I 1 (N 1 /N 2 ) = 25( 1000/5000) = 5 Amps. 3. P 1 = P 2 : V 1 I 1 = V 2 I 2 = 2500 Watts Givens: V 1 = 100 N 1 = 1000 N 2 = 5000 I 1 = Solve for V 2 : V 2 = V 1 (N 2 /N 1 ) = 100( 5000/1000) = 500 Volts 2. Solve for I 2 : I 2 = I 1 (N 1 /N 2 ) = 25( 1000/5000) = 5 Amps. 3. P 1 = P 2 : V 1 I 1 = V 2 I 2 = 2500 Watts

Step Down Transformer N 2 <N 1 Example: A transformer plugged into the wall ( 120V) charges a 9 volt battery. 1. What is the turn ratio (N 1 /N 2 ) ? 2. What is the secondary current if the primary current is.5A? 3. What is the power in the primary and secondary? Example: A transformer plugged into the wall ( 120V) charges a 9 volt battery. 1. What is the turn ratio (N 1 /N 2 ) ? 2. What is the secondary current if the primary current is.5A? 3. What is the power in the primary and secondary?

Solve the Problem Givens: V 1 = 120 V 2 = 9 I 1 =.5 1. Solve for (N 2 /N 1 ) : V 2 = V 1 (N 2 /N 1 ) so (N 2 /N 1 ) = V 2 /V 1 = 9/120 = Solve for I 2 : I 2 = I 1 (N 1 /N 2 ) =.5 ( 1 /.075) = 6.67Amps. 3. P 1 = P 2 : V 1 I 1 = V 2 I 2 = 60 Watts Givens: V 1 = 120 V 2 = 9 I 1 =.5 1. Solve for (N 2 /N 1 ) : V 2 = V 1 (N 2 /N 1 ) so (N 2 /N 1 ) = V 2 /V 1 = 9/120 = Solve for I 2 : I 2 = I 1 (N 1 /N 2 ) =.5 ( 1 /.075) = 6.67Amps. 3. P 1 = P 2 : V 1 I 1 = V 2 I 2 = 60 Watts

AC Voltage and Current

Example What is the peak voltage for household voltage of 120V(rms)? V(peak) = 1.41(120) = 169 Volts