Warm-up Why do loops of wire in a motor rotate? What is similar between Electric motor, and Electric meter? What is electromagnetic induction? Name 4 objects that apply electromagnetic induction.

Chapter 37: Electromagnetic Induction Faraday discovered: Magnetic and Electric fields interact to produce a Force. (3rd right hand rule) Magnetism can produce electric current in a wire!! How so? Michael Faraday

Electromagnetic Induction The phenomenon of inducing voltage in a conductor by changing the magnetic field near a conductor is known as Electromagnetic Induction Magnetic field changes when either the magnet or the coil moves or when they both move.

Faradays experiment Molecular Expressions: Electricity and Magnetism - Interactive Java Tutorials: Faraday's Magnetic Field Induction Experiment

Induced Voltage? why is the phrase Induced voltage used instead of induced current? Answer: In order for current to flow between two points of a conductor, there must be a difference of potential between those points. That potential difference is the voltage. Therefore, Voltage is induced first in order for current to flow.

Electromagnetic induction video http://glencoe.com/sec/science/physics/ppp_09/animation/Chapter%2025/Electromagnetic%20Induction.swf

Magnitude of the induced voltage What factors affect the magnitude of the induced voltage? Answer: The rate (R) at which Flux (magnetic field) is changing, The number of coils/turns (N) of the conductor

The Faradays law. Induced voltage (V) in a coil is proportional to the product of; the rate (r) at which the magnetic field changes within the loops, and Number (n) of loops (turns /coils)

Question; Why is it hard to move the magnet into the coil if the coil has many loops?

Lenz’s Law The law notes that; an induced voltage always produces a magnetic field that opposes the field that originally produced it.

Lenz’s law

Application of electromagnetism Generator The coil is rotated mechanically using one’s hand, Other ways of rotating the coil include Water-hydro power Wind- wind mills Steam- Geothermal, Nuclear Reactors

application Name 4 objects that apply electromagnetic induction. Transformer Generator Motor Electro magnet

Homework Textbook pg 592 # 1-10

The transformers

A simple transformer A simple transformer is a set of induction coils as shown below. Primary coil induces voltage onto the secondary coil

Primary and secondary coils A common transformer is made up of an iron core and two coils of wires as shown below. The Primary coil is connected to the power source. The secondary coil gets induced with current.

What does it do? Molecular Expressions: Electricity and Magnetism - Interactive Java Tutorials: Transformer

Induction process (Mutual induction) Happens when current in the primary is changing (increasing or decreasing). Changing current induces a magnetic field that is changing continuously on the core, a condition necessary for induction of voltage continuously on to the secondary coil. When current is not changing (increasing or decreasing), there is no induction taking place.

Why is the AC preferred to DC? We can increase and decrease current flow by opening and closing (Switching off and on) the circuit continuously when using a DC current, or just use AC current. The Ac is changing continuously

Why is an Iron core preferred to two coils apart? Answer: Iron core concentrates the magnetic field within itself by forming loops that get into contact with the secondary coil. These loops of magnetic field induce voltage in the secondary coil.

Step up Transformers The number of coils in the secondary and primary determines whether a transformer is a step up or step down transformer. less number of coils in primary more number of coils in secondary

Step down Transformers Notice that power transferred is the same. More number of turns in primary coil Less number of turns in secondary

What is the relationship between primary voltage, secondary voltage and the number of turns? Answer:

The relationship between in-put and out-put power is: Power input = power output.

Class work & Homework Textbook Page 592, # 11-15 Hm WK Textbook page 594, # 34-42