Generator and Transformer

Moving ConductorIf a straight conductor is moved in a path perpendicular to a magnetic field, a current is induced in the conductor

No current flows though since not a loop

Induced emf

= B l v

l – length of conductor

v – velocity of conductor

Example

An airplane travels at 1000 km/hr in region where the Earth’s magnetic field in 5.0 x 10-5 T. What is the emf induced between the wing tips that are 70m apart?

Generators (Dynamo)

Transforms mechanical energy into electric energyCoil of wire spins in the presence of a permanent magnetic field Induces are current in the coilCurrent produced actually fluctuates as the coils position in the field changesProduces a current that switches direction every half a rotation – Called Alternating Current (AC)

Moving ElectricityHow does electric energy transmit over large distances?Much less energy is lost when it travels at a higher V and lower I

Transformer

Device that changes voltages

Two coils around an iron core

Current supplied to the primary coil induces a current in the secondary coil

By varying the number of windings in the coils you can vary the potentials

Equation

P S S

S P P

I V N

I V N

Types

Step-up – more windings on the secondary coil increases the voltage

Step-down – less windings on the secondary coil decreases the voltage

Transformers work only on AC current. Why?

Transportation

Electric energy is stepped up for transmission and then stepped down for household use

Problem 1

A metal airplane with a wing span of 30m flies horizontally at a constant speed of 320 km/h in a region where the Earth’s magnetic field is 5.0 x 10-5 T. What is the induced emf across its wing tips?

Problem 2

A 20 cm long metal rod is moving at a speed of 10 m/s in a magnetic field of 0.30 T. Find

a) the induced emf in the rod

b) the current in the rod

Problem 3

An ideal transformer steps 8.0 V up to 2000 V, and the 4000 turn secondary coil carries a current of 2.0 A. Find

a) the number of turns in the primary

coil.

b) the current in the primary coil

Problem 4

The primary coil of an ideal transformer has 720 turns, and the secondary coil has 180 turns. If the primary coil carries 15 A at a voltage of 120 V, for the secondary coil what are the

a) voltage

b) current