It is against the honor code to “click” for someone else-violators will loose all clicker pts.HITT RF Remote Login Procedure:

1. PRESS AND HOLD THE DOWN ARROW KEY until the GREEN light on the remote turns RED.

2. PRESS THE “0” KEY and you will see the RED light flash GREEN.

3. PRESS THE “9” KEY and you will see the RED light flash GREEN.

4. PRESS AND RELEASE THE DOWN ARROW KEY again and you will see the red light search for the receiver, if it BLINKS GREEN MULTIPLE TIMES you are logged in.

The radio channel number for this room is “09” (zero, nine). It is STRONGLY recommended to login your remote for every class justto be sure it is on the correct radio channel and working before class.

The Electric Vector in Light WavesPolarization of Light Waves

Each atom produces a wave with its own orientation of

All directions of the electric field vector are equally possible and lie in a plane perpendicular to the direction of propagation

E

This is an unpolarized wave

Polarized Light A wave is said to be linearly

polarized if the resultant electric field vibrates in the same direction at all times at a particular point

It may vibrate in any fixed direction Quiz

Polarization can be obtained from an unpolarized beam by A. selective absorptionB. reflectionC. ScatteringD. All of the aboveE. None of the above

Polarization by Selective Absorption

The most common technique for polarizing light Uses a material that transmits waves whose

electric field vectors in the plane are parallel to a certain direction and absorbs waves whose electric field vectors are perpendicular to that direction

E. H. Land discovered a material that polarizes light through selective absorption

He called the material Polaroid

Polarization by Reflection When an unpolarized light beam is reflected

from a surface, the reflected light is Completely polarized Partially polarized Unpolarized

It depends on the angle of incidence If the angle is 0° or 90°, the reflected beam is unpolarized For angles between this, there is some degree of

polarization For one particular angle, the beam is completely polarized

The angle of incidence for which the reflected beam is completely polarized is called the polarizing angle θp

θp is called Brewster’s Anglesin tancos

pp

p

n

Liquid Crystal Displays (LCDs) One use of polarized Light

A liquid crystal is intermediate between a crystalline solid and a liquid

The molecules of the substance are more orderly than those of a liquid but less than those in a pure crystalline solid

In a display, the liquid crystal is placed between two glass plates with electrical contacts

A voltage is applied across any segment in the display and that segment turns on

V=0 rotates Polarization 90° making it Bright

Light passes through the polarizer on the right and is reflected back to the observer, who sees the segment as being bright

The light is absorbed by the polarizer on the right and none is reflected back to the observer

V≠0 produces no rotation making it Dark

Magnetism-Magnetic Fields Poles of a magnet are the ends where objects

are most strongly attracted Two poles, called north and south

Like poles repel each other and unlike poles attract each other Similar to electric charges

Magnetic poles cannot be isolated If a permanent magnetic is cut in half

repeatedly, you will still have a north and a south pole

This differs from electric charges There is some theoretical basis for

monopoles, but none have been detected

Sources of Magnetic Fields The region of space surrounding a

moving charge includes a magnetic field The charge will also be surrounded by

an electric field A magnetic field surrounds a properly

magnetized magnetic material Soft magnetic materials, such as iron, are

easily magnetized They also tend to lose their magnetism

easily Hard magnetic materials, such as cobalt and

nickel, are difficult to magnetize They tend to retain their magnetism

Magnetic Fields Symbolized by Direction is given by the direction a north pole

of a compass needle points in that location Magnetic field lines can be used to show how

the field lines, as traced out by a compass, would look

B

Earth’s Magnetic Field The Earth’s geographic north pole corresponds

to a magnetic south pole The Earth’s geographic south pole corresponds

to a magnetic north pole Strictly speaking, a north pole should be a

“north-seeking” pole and a south pole a “south-seeking” pole

Quick Quiz The red end of a compass needle which points

“North” is which end of a dipole magnet? A. North pole B. South pole

Electric Charges in Magnetic Fields Moving charges feel magnetic force

perpendicular to path of This force has a maximum value when

the charge moves perpendicularly to the magnetic field lines This force is zero when the charge moves

along the field lines This force is zero if the charge is stationary

Superconducting magnets 300000 Gauss or 30 Tesla

Earth’s magnetic field 0.5 G or 5 x 10-5 T

sinBqvF Quick Quiz How many G in a T?A. 10-5 D. 105

B. 10-4 E. 0.5 x 10-5

C. 104

Right Hand Rule Place your fingers in the

direction of Curl the fingers in the

direction of the magnetic field,

Your thumb points in the direction of the force, , on a positive charge

If the charge is negative, the force is opposite that determined by the right hand rule

v

B

F