Generator and Transformer

Moving Conductor If 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 T. What is the emf induced between the wing tips that are 70m apart?

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

Moving Electricity How 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

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 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