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Magnetic Domains – Randomly Oriented~1015 atoms in each domain

Magnetic Domains – Aligned

http://www.acesinternational.org/images/32NE0012.GIF

Magnetic field around a current-carrying wire (RHR #1)

Magnetic field lines due to a circular loop of wire

Force on a current-carrying wire place in a magnetic field B

(RHR #2)

Magnetic Force on Current-carrying Wire

•F = I L B–I: current in Amps–L: length in meters –B: magnetic field in Tesla

Magnetic Force on Charged Particle

•magnitude: F = qvB–q: charge in Coulombs–v: speed in meters/second

–B: magnetic field in Tesla•direction: Right Hand Rule

Magnetic Forces can...

•accelerate charged particles by changing their direction

•cause charged particles to move in circular or helical paths

Electromagnetic Induction

Induced Emf and Induced Current

There are a number of ways a magnetic field can be used to generate an electric current.

It is the changing field that produces the current.

Induced Emf and Induced Current

The current in the coil is called the induced current because it is broughtabout by a changing magnetic field.

Since a source emf is always needed to produce a current, the coil behavesas if it were a source of emf. This emf is known as the induced emf.

Induced Emf and Induced Current

An emf can be induced by changing thearea of a coil in a constant magnetic field

In each example, both an emf and a current are induced because the coil is part of a complete circuit. If the circuit were open, therewould be no induced current, but there would be an induced emf.

The phenomena of producing an induced emf with the aid of amagnetic field is called electromagnetic induction.

Motional Emf

THE EMF INDUCED IN A MOVING CONDUCTOR

Each charge within the conductoris moving and experiences a magnetic force

qvBF

The separated charges on theends of the conductor give riseto an induced emf, called amotional emf.

Motional Emf

vBLE

Motional emf when v, B, and L are mutually perpendicular

Motional Emf

(a) V 4.6m 6.1T 80.0sm0.5 vBLE

A 067.096

V 4.6

RI

E(b)

Magnetic Flux

GRAPHICAL INTERPRETATION OF MAGNETIC FLUX

The magnetic flux is proportionalto the number of field lines that passthrough a surface.

Magnetic Flux

ttt o

o

E

Faraday’s Law of Electromagnetic Induction

FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION

The average emf induced in a coil of N loops is

tN

ttN

o

o

E

SI Unit of Induced Emf: volt (V)

Faraday’s Law of Electromagnetic Induction

Example: The Emf Induced by a Changing Magnetic Field

A coil of wire consists of 20 turns each of which has an area of 0.0015 m2.A magnetic field is perpendicular to the surface. Initially, the magnitude of the magnetic field is 0.050 T and 0.10s later, it has increased to 0.060 T.Find the average emf induced in the coil during this time.

V 100.3

s 0.10

T 050.0T 060.00cosm 0015.020cos

coscos

3

2

t

BBNA

t

ABBAN

tN

o

o

E

Faraday’s Law of Electromagnetic Induction

Conceptual Example 7 An Induction Stove

Two pots of water are placed on an induction stove at the same time.The stove itself is cool to the touch. The water in the ferromagneticmetal pot is boiling while that in the glass pot is not. How can sucha cool stove boil water, and why isn’t the water in the glass pot boiling?

Lenz’s Law The induced current will

flow in a direction so as to oppose the change in flux.

Use in combination with hand rule to predict direction of induced current.