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

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

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

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  1. The radio channel number for this room is “09” (zero, nine). It is STRONGLY recommended to login your remote for every class just to be sure it is on the correct radio channel and working before class. It is against the honor code to “click” for someone else-violators will loose all clicker pts.HITT RF Remote Login Procedure: PRESS AND HOLD THE DOWN ARROW KEY until the GREEN light on the remote turns RED. PRESS THE “0” KEY and you will see the RED light flash GREEN. PRESS THE “9” KEY and you will see the RED light flash GREEN. 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.

  2. 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 This is an unpolarized wave

  3. 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 • Polarization can be obtained from an unpolarized beam by • selective absorption • reflection • scattering

  4. 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

  5. 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 angleθp • θp is called Brewster’s Angle

  6. 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

  7. 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

  8. V≠0 produces no rotation making it Dark • The light is absorbed by the polarizer on the right and none is reflected back to the observer

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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 Quick Quiz • How many G in a T? • 10-5 D. 105 • 10-4 E. 0.5 x 10-5 • 104

  14. 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

  15. Magnetic Force on a Current Carrying Conductor • A force is exerted on a current-carrying wire placed in a magnetic field • The current is a collection of many charged particles in motion • The direction of the force is given by right hand rule #1

  16. Force on a Wire • The blue x’s indicate the magnetic field is directed into the page • The x represents the tail of the arrow • Blue dots would be used to represent the field directed out of the page • The • represents the head of the arrow • In this case, there is no current, so there is no force

  17. Force on a Wire,cont • B is into the page • The current is up the page • The force is to the left

  18. Force on a Wire,final • B is into the page • The current is down the page • The force is to the right

  19. Force on a Wire, equation • The magnetic force is exerted on each moving charge in the wire • The total force is the sum of all the magnetic forces on all the individual charges producing the current • F = B I ℓ sin θ • θ is the angle between and the direction of I • The direction is found by the right hand rule, placing your fingers in the direction of I instead of

  20. Force on a Charged Particle in a Magnetic Field • Consider a particle moving in an external magnetic field so that its velocity is perpendicular to the field • The force is always directed toward the center of the circular path • The magnetic force causes a centripetal acceleration, changing the direction of the velocity of the particle

  21. Force on a Charged Particle • Equating the magnetic and centripetal forces: • Solving for r: • r is proportional to the momentum of the particle and inversely proportional to the magnetic field • Sometimes called the cyclotron equation

  22. Particle Moving in an External Magnetic Field • If the particle’s velocity is not perpendicular to the field, the path followed by the particle is a spiral • The spiral path is called a helix

  23. Hans Christian Oersted • 1777 – 1851 • Best known for observing that a compass needle deflects when placed near a wire carrying a current • First evidence of a connection between electric and magnetic phenomena

  24. Magnetic Fields – Long Straight Wire • A current-carrying wire produces a magnetic field • The compass needle deflects in directions tangent to the circle • The compass needle points in the direction of the magnetic field produced by the current

  25. Direction of the Field of a Long Straight Wire • Right Hand Rule #2 • Grasp the wire in your right hand • Point your thumb in the direction of the current • Your fingers will curl in the direction of the field

  26. Magnitude of the Field of a Long Straight Wire • The magnitude of the field at a distance r from a wire carrying a current of I is • µo = 4  x 10-7 T.m / A • µo is called the permeability of free space

  27. Ampère’s Law • André-Marie Ampère found a procedure for deriving the relationship between the current in an arbitrarily shaped wire and the magnetic field produced by the wire • Ampère’s Circuital Law • B|| Δℓ = µo I • Sum over the closed path

  28. Ampère’s Law, cont • Choose an arbitrary closed path around the current • Sum all the products of B|| Δℓ around the closed path

  29. Ampère’s Law to Find B for a Long Straight Wire • Use a closed circular path • The circumference of the circle is 2  r • This is identical to the result previously obtained

  30. André-Marie Ampère • 1775 – 1836 • Credited with the discovery of electromagnetism • Relationship between electric currents and magnetic fields • Mathematical genius evident by age 12

  31. Magnetic Force Between Two Parallel Conductors • The force on wire 1 is due to the current in wire 1 and the magnetic field produced by wire 2 • The force per unit length is:

  32. Force Between Two Conductors, cont • Parallel conductors carrying currents in the same direction attract each other • Parallel conductors carrying currents in the opposite directions repel each other

  33. Magnetic Field of a Current Loop • The strength of a magnetic field produced by a wire can be enhanced by forming the wire into a loop • All the segments, Δx, contribute to the field, increasing its strength

  34. Magnetic Field of a Current Loop – Total Field

  35. Magnetic Field of a Current Loop – Equation • The magnitude of the magnetic field at the center of a circular loop with a radius R and carrying current I is • With N loops in the coil, this becomes

  36. Magnetic Field of a Solenoid • If a long straight wire is bent into a coil of several closely spaced loops, the resulting device is called a solenoid • It is also known as an electromagnet since it acts like a magnet only when it carries a current

  37. Magnetic Field of a Solenoid, 2 • The field lines inside the solenoid are nearly parallel, uniformly spaced, and close together • This indicates that the field inside the solenoid is nearly uniform and strong • The exterior field is nonuniform, much weaker, and in the opposite direction to the field inside the solenoid

  38. Magnetic Field in a Solenoid, 3 • The field lines of the solenoid resemble those of a bar magnet

  39. Magnetic Field in a Solenoid, Magnitude • The magnitude of the field inside a solenoid is constant at all points far from its ends • B = µo n I • n is the number of turns per unit length • n = N / ℓ • The same result can be obtained by applying Ampère’s Law to the solenoid

  40. Magnetic Field in a Solenoid from Ampère’s Law • A cross-sectional view of a tightly wound solenoid • If the solenoid is long compared to its radius, we assume the field inside is uniform and outside is zero • Apply Ampère’s Law to the blue dashed rectangle

  41. Magnetic Effects of Electrons – Orbits • An individual atom should act like a magnet because of the motion of the electrons about the nucleus • Each electron circles the atom once in about every 10-16 seconds • This would produce a current of 1.6 mA and a magnetic field of about 20 T at the center of the circular path • However, the magnetic field produced by one electron in an atom is often canceled by an oppositely revolving electron in the same atom

  42. Magnetic Effects of Electrons – Orbits, cont • The net result is that the magnetic effect produced by electrons orbiting the nucleus is either zero or very small for most materials