APRIL 4TH 2011

Electromagnetic Induction

The Discovery

In 1822, Michael Faraday wrote a goal in his notebook: “Convert Magnetism into Electricity”..... Nearly 10 years later he was able to demonstrate that a changing magnetic field could produce an electric current.

What is Electromagnetic Induction(EMI)?

Current is produced in a conductor when it is moved through a magnetic field because the magnetic lines of force are applying a force on the electrons in the conductor and causing them to move.

This process of generating current in a conductor by placing the conductor in a changing magnetic field is called induction.

Electro Induction

What is EMI Cont.

This is called induction because there is no physical connection between the conductor and the magnet.

The conductor, which is often a piece of wire, must be perpendicular to the magnetic lines of force in order to produce the maximum force on the electrons. 

Direction of the Current

The direction that the induced current flows is determined by the direction of the lines of force and by the direction the wire is moving in the field.  

To find the force charges in the wire, use the third right hang rule; hold you right hand so that your thumb points in the direction in which the wire is moving and your fingers point in the direction of the magnetic field. Your palm will point in the direction of the current flow. (refer to diagram below)

Diagram

N S

Electromotive Force

Electromotive Force (EMF): it is the force that makes electrons move in a certain direction within a conductor.

Even though it is called a force, it is a potential difference and is measured in volts.

If the moving wire is part of a close circuit, the EMF will cause a current to flow in the direction of the EMF.

Factors affects EMF

The magnetic field – B (T)The length of the wire – L (m)The velocity of the wire in the field – v (m/s)Formula:

EMF = BLv

Ex. 1

A straight wire 0.20m long move perpendicularly through a magnetic field induction of 8.0x 10 -2 T at a speed of 7.0m/s. a. What EMF is induced on the wire? b. The wire is part of a circuit that has a resistance of 0.50Ω, what current flows in the circuit?

L = 0.20m, B = 8.0x 10 -2 T , v = 7.0m/s, R = 0.50 Ω

Solution.

a) EMF = BLv = (8.0x 10 -2 T) (0.20m) (7.0m/s) = (8.0x 10 -2 N/Am) (0.20m)

(7.0m/s) = 0.11 (N/Am)(m)(m/s) = 0.11 W/A = 0.11 V

b) I = V/R = (0.11V/0.50Ω) = 0.22A

Homework.

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