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CHAPTER 19: MAGNETISM

CHAPTER 19: MAGNETISM. Magnets, Magnetic Fields, Magnetic Force, & Electricity. PROPERTIES OF MAGNETS. A magnet has 2 poles – north & south Like poles repel, opposites attract If you break a magnet, the 2 new pieces will have a north and south pole.

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CHAPTER 19: MAGNETISM

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  1. CHAPTER 19:MAGNETISM Magnets, Magnetic Fields, Magnetic Force, & Electricity

  2. PROPERTIES OF MAGNETS • A magnet has 2 poles – north & south • Like poles repel, opposites attract • If you break a magnet, the 2 new pieces will have a north and south pole. • Some metals can become magnetized by being brought near a magnet. They are called temporary magnets.

  3. MAGNETIC FIELDS AROUND MAGNETS • Just like electric and gravitational forces result from electric and gravitational fields, magnetic forces result from magnetic fields. • These fields move from north to south. • A compass always points from the North to the South (called the magnetic north).

  4. THE EARTH’S MAGNETIC FIELD • The magnetic north does not coincide with the geographic North Pole since the axis of the Earth’s magnetic field does not lie along its rotational axis. • The Earth’s magnetic field fluctuates. • On a long time scale, the poles have switched polarity several times in the past (most recently 700,000 years ago. • On a short scale, it has moved roughly 110 km (70 mi) northward per decade from its 1904 latitude position!

  5. MAGNETIC INDUCTION • The strength of a magnetic field is called magnetic induction. • It is symbolized by B • It is measured in Teslas (T). 1 T = 1N/A.m • Once the magnetic field strength is determined, the force on any charged particle moving at any speed can be found as long as the direction remains perpendicular to the magnetic field!

  6. MAGNETIC FORCE We can use two formulas to find magnetic force: F = qvB If the direction of the charged particle’s velocity is not perpendicular to the magnetic field then: F = qvB(sinΘ) Where B = magnetic field strength I = current q = charge v = velocity of charge

  7. RIGHT-HAND FORCE RULE FOR CHARGES • Determines the direction of force in a magnetic field. • Use your right hand! • Point your fingers in the direction of the charged particle’s velocity • Now, curl your fingers in the direction of the magnetic field. • Your thumb points in the direction of the magnetic force.

  8. ANOTHER RIGHT-HAND FORCE RULE! • An alternate is known as the “palm method” for determining the magnetic force: • Point your thumb in the direction of the charged particle’s velocity • Point your fingers in the direction of the magnetic field. • Your palm now faces the direction of the magnetic force.

  9. Magnetism from Electricity • Hans Christian Oersted found that a compass needle was deflected when brought near a current-carrying wire. • We can find the direction of this current using the “right hand source rule”.

  10. RIGHT-HAND SOURCE RULE • Determines the direction of the magnetic field in a current carrying wire. • Again, use your right hand! • Grasp the wire so that your thumb points in the direction of the current. • Your curled fingers point in the direction of the magnetic field.

  11. FORMULAS FOR MAGNETIC FIELDS • There are several formulas to use for determining the strength of a magnetic field in current-carrying wires. • Near a long straight wire: B = μo I 2d where μo = 4 x 10-7 Tm/A (this is called the magnetic permeability of free space)

  12. MORE FORMULAS FOR MAGNETIC FIELDS • At the center of circular loop: B = μo I 2r • At the center of a solenoid, which is a long wire wound in a tight coil. B = μoNIB = μonI L Where N = number of loops or turns and n = number of turns per meter or (N/L)

  13. MAGNETIC FORCES & WIRES • Just as a charged particle moving in a magnetic field experiences a force, so does a current-carrying wire since it is made up of many moving charges! • We can use formulas and another right-hand rule to find this force!

  14. MAGNETIC FORCE ON WIRES We can use two formulas to find magnetic force: F = BIL If the wire is not perpendicular to the magnetic field then: F = BIL(sinΘ) Where B = strength of magnetic field I = current q = charge L= length of wire

  15. RIGHT-HAND FORCE RULE FOR WIRES • Determines the direction of force in a magnetic field. • Use your right hand! • Point your fingers in the direction of the current. • Now, curl them in the direction of the magnetic field. • Your thumb points in the direction of the magnetic force on the wire.

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