Units Tesla (SI) N/(Cm/s) N/(Am) Gauss 1 T = 10 4 gauss

UnitsTesla (SI)

N/(Cm/s)N/(Am)

Gauss1 T = 104 gauss

MagneticDipole

MagneticField (B)

Magnetic MonopolesDo not exist!

In this way they differ from electric dipoles, which can be separated into electric monopoles.

Magnetic Force on Charged Particle

magnitude: F = qvBsin–q: charge in Coulombs–v: speed in meters/second–B: magnetic field in Tesla: angle between v and B

direction: Right Hand Rule

Magnetic ForceCalculate the magnitude and direction of the magnetic force.

v = 300,000 m/s

B = 200 mT

q = 3.0C

34o

Magnetic FieldsFormed by moving charge

Affect moving charge

Magnetic Forces can...

accelerate charged particles by changing their direction

cause charged particles to move in circular or helical paths

Magnetic Forces cannot...

change the speed or kinetic energy of charged particles

do work on charged particles

When v and B are at right angles to each other...

BV

F

V

F

V

F

V

F

qvBsin = mv2/rqB = mv/r

q/m = v/(rB)

Electric and Magnetic Fields Together

E

B

v = E/B

q

Magnetic Force on Current-carrying WireF = I L B sin

–I: current in Amps–L: length in meters –B: magnetic field in Tesla: angle between current and field

Magnetic Field forLong Straight Wire

B = oI/(2r)o: 4 10-7Tm/A

•magnetic permeability of free space

•I: current (A)•r: radial distance from center of wire (m)

Hand Rule

Curve your fingers Place your thumb (which is

presumably pretty straight) in direction of current.

Curved fingers represent curve of magnetic field.

Field vector at any point is tangent to field line.

i

r•

For straight currents

I

Principle of Superposition

When there are two or more currents forming a magnetic field, calculate B due to each current separately and then add them together using vector additionvector addition.

Beyond the 4th Grade

I

Magnetic Field Inside aSolenoid

B = onIo: 4 10-7Tm/A•n: number of coils per unit length

•I: current (A)

Lab: Magnetic Field Map

I

Using a compass, map the magnetic field inside and outside your solenoid. Show the following:

a) Tracing of solenoid (true size)b) Current through solenoidc) Connection to DC outletd) Field lines mapped with compass e) Edge effects (What happens to

those field lines farther away from the solenoid? Can you explain it?)

f) North and South Poles of solenoidg) The Compass Roseh) One drawing per group (Write all

names on paper)

Lab EvaluationMagnetic Field Map

A) Are field lines visible in the core of the solenoid?

B) Are the directions of the field lines in the core consistent with the Right Hand Rule?

C) Are the North and South Poles correctly identified?

Magnetic Flux The product of

magnetic field and area. Can be thought of as a

total magnetic “effect” on a coil of wire of a given area.

Magnetic Flux B = BAcos

B: magnetic flux in Webers (Tesla meters2)

B: magnetic field in TeslaA: area in meters2.: the angle between the

area and the magnetic field.

Magnetic Flux A system will respond

so as to oppose changes in magnetic flux.

Changing the magnetic flux can generate electrical current.

Faraday’s Law of Induction = -NB/t

induced potential (V)N: # loopsB: magnetic flux

(Webers, Wb) t: time (s)

A closer look … = -B/t = -(BAcos)/tTo generate

voltageChange BChange AChange

Lenz’s Law The current will flow in a

direction so as to oppose the change in flux.

Use in combination with hand rule to predict current direction.

Announcements–AP Review every morning at 7:00 AM.

–Lunch Bunch tomorrow (come with pretest completed).

–Exam Thursday–1988 AP Free Response: Thursday and Friday, after school or at lunch

Challenge Problem #3How large a force is needed to move the rod at a constant speed of 2 m/s? How much power is dissipated in the resistor?

B = 0.15 T

v = 2 m/s

50 cm3