Electromagnetic Induction

A.S. 12.1.1 – 12.1.6 due Friday, 12/19/14

What happens to electrons as they move

through a magnetic field?

What would happen if there were a LOT of electrons…like in a wire…

Things to think about…

Electrons experience a force when moving

through a magnetic field If the electrons are in a wire, they all

experience a force and will move in the direction of the force

Result: A net shift in charge so that one side of the wire is more negative than the other

End result: There is an electric field created in the wire due to the separation of charges:

What happens…

The electrons (charge = e) will continue to

move to one end of the wire UNTIL… The force of electrostatic repulsion balances

the force from the magnetic field:

Induced (motional) emf

Known: An electric current produces a

magnetic field Known: A wire moving through

(perpendicular to) a magnetic field will develop a potential difference across its ends (Induced emf)

More difficult? Producing a current…

Electromagnetic Induction

What happens to the current

when: North end moved into the loop? North end moved out of the loop? South end moved into the loop? South end moved out of the loop? North end held above the plane of the loop? Magnet held inside the loop? Magnet moved in/out of the loop at a different

speed than before?

Observations

As these increase, so will the current: The relative speed of the magnet with respect to

the loop/coil Strength of the magnetic field Number of turns in the coil Area of the loop

ALSO: Angle of the magnetic field relative to the plane of

the loop. At an angle 90° (field perpendicular to the plane

of the loop), the current will be the maximum possible for the conditions

Variables that affect current:

British Physicist and Chemist—born 1791, died 1867 Self-taught…discovered many concepts, had

difficulties with some of the math Discovered Electromagnetic Induction in 1831

(also devised the laws relating to electrolysis and the deposition of ions onto metals through the use of electricity)

Found the connecting link between each of the observations we just made…

The relevant law that bears his name (Faraday’s Law) relates to electromagnetism

Michael Faraday

The strength of the magnetic field crossing

the plane of a loop of area, A

B = magnetic field strength A = area of the loop q = angle between the magnetic field

direction and the normal to the plane of the loop

Magnetic Flux

Units of flux = Weber (Wb)

Conceptual visualization: flux is the number of magnetic field lines that are passing through the plane of the loop

Increase the flux by: Increasing the area of the loop Increasing the strength of the field (more field lines…) Making the loop and field lines more perpendicular

Magnetic Flux

Same as magnetic flux…but specifically when

there is more than 1 loop in a coil.

N = number of loops in the coil

Magnetic Flux Linkage

A loop of area 2.00 cm2 is in a constant

magnetic field of 0.100 T. What is the magnetic flux through the loop in each of the following situations: When the loop is perpendicular to the field When the loop is parallel to the field When the normal to the loop and the field have

an angle of 60.0° between them?

Sample Problem

The induced emf is equal to the (negative

value for) rate of change of magnetic flux:

The induced emf, therefore, can cause a current in a conducting wire…but this will ONLY happen when there is a changing magnetic flux!

Faraday’s Law

The magnetic field through a single loop of

area 0.250 m2 is changing at a rate of 4.25 T·s-

1. What is the induced emf in the loop?

Sample Problem