Presentation on theme: "Electromagnetic Induction Can a magnet produce electricity?"— Presentation transcript:
Electromagnetic Induction Can a magnet produce electricity?
Michael Faraday An English scientist who was first to prove that a magnet can produce current. A magnet can produce electricity! Duh! Joseph Henry
What conditions are necessary for a magnet to produce current? Magnet must be moving or Wire must be moving Movement causes changing magnetic field Changing magnetic field induces current
Electromagnetic Induction The phenomenon by which an emf or current induced in a conductor due to change in magnetic field.
What factors affect the nature of emf or current produced? Direction of motion In or out Speed of motion Polarity of magnet coming in Number of turns Area of coil
Direction of Motion The direction of the current induced opposes the change producing it
Speed of Motion The faster the movement is, the greater is the induced emf.
Polarity of magnet The induced current produces a magnetic field that opposes the one causing it. Use RHR
Number of turns The more the number of turns, the greater the emf induced.
Laws of EM induction Faraday’s Law The induced emf across the conductor is equal to the rate at which magnetic flux is cut by the conductor.
Magnetic Flux Product of flux density (B) and the area (A), when flux is at right angles to the area. Ø= BA Unit: Weber, Wb A weber is the flux when a unit tesla of magnetic flux density is at right angles to a unit area.
Magnetic Flux Linkage Total flux cut by all turns of the coil Ø= BAN
So far… EMF = d Ø /dt For single coil EMF = BA/t For many coils EMF = BAN/t For a wire EMF = Blx/t Where l is length of wire and x is distance traveled. EMF = Blv Where v is the speed
Lenz’s Law The direction of any induced current is such as to oppose the change that causes it.
Therefore EMF = - d Ø /dt For single coil EMF = - BA/t For many coils EMF = - BAN/t For a wire EMF = - Blx/t Where l is length of wire and x is distance traveled. EMF = - Blv Where v is the speed
Example 1 A straight wire of length 0.2 m moves at a steady speed of 3 ms -1 at right angles to a magnetic field of flux density 0.1 T. What will be the emf induced across the ends of the wire?
Example 2 A coil of wire having 2500 turns and of area 1 cm 2 is placed between the poles of a magnet so that the magnetic flux passes perpendicularly through the coil. The flux density of the field is 0.5 T. The coil is pulled rapidly out of the field in a time of 0.1 s. What average emf is induced across the ends of the coil?