Magnetic Fields and Applications

MAGNETISM

  • Magnetic Poles
    • Each end of a magnet is known as a magnetic pole.
    • Like magnetic poles repel each other; unlike poles attract.
    • Magnets are dipolar, creating a dipole field.
    • A suspended magnet orients along the north-south axis.
    • The Earth's geographic North Pole is near the magnetic South Pole of Earth.

MAGNETIC FIELD

  • Definition

    • Magnetic field lines surround a magnet.
    • The direction of the magnetic field indicates where a compass would point.
    • The strength of the magnetic field (B) is measured in tesla (T).

  • Strength of Magnetic Field (B T)

    • Closer magnetic field lines indicate stronger magnetic field strength.
    • The strength decreases as the distance from the magnet increases.
    • The resultant magnetic field direction at a point is vector sum of individual fields.
    • Static magnetic fields have fixed magnitude and direction.
    • Uniform magnetic fields have evenly distributed field lines.

MAGNETIC FIELDS AND CURRENT-CARRYING WIRES

  • A circular magnetic field forms around a wire with current.
  • The magnetic field is perpendicular to the direction of current and varies based on the current's direction.
  • Right-Hand Grip Rule
    • Thumb points current direction; fingers show magnetic field direction.

MAGNETIC FIELDS BETWEEN PARALLEL WIRES

  • Two parallel current-carrying wires produce their own magnetic fields.
  • Interaction of fields can cause attraction or repulsion depending on their directions:
    • Opposing directions result in attraction (unlike poles).
    • Same direction results in repulsion (like poles).

MAGNETIC FIELD AROUND A SOLENOID

  • Multiple loops of wire (solenoid) create a stronger magnetic field.
  • Magnetic field resembles that of a bar magnet.
  • Determining Direction:
    • Right-hand rule: Point fingers along coil current direction; thumb points field direction.

CREATING AN ELECTROMAGNET

  • An electromagnet uses electricity to generate a magnetic field.
  • Strength can be increased by:
    • Increasing current.
    • Increasing turns of wire per unit length.
    • Inserting a soft iron core.

FORCES ON CHARGED OBJECTS DUE TO MAGNETIC FIELDS

  • Charged particles in a magnetic field experience forces.

  • Lorentz Force:

    • Given by F = q v B
    • Force maximizes at right angles to the magnetic field.

  • Direction of Force:

    • Right-hand rule determines force direction for positive charges.

THE FORCE ON A CURRENT-CARRYING CONDUCTOR

  • Similar to charged particles, conductors in a magnetic field experience forces.
  • Maximum force occurs when the conductor is perpendicular to the magnetic field.
  • Force is given by F = n I l B

DIRECTION AND SHAPE OF FIELDS

  • Uniform fields show evenly spaced lines; radial fields do not.
  • Static fields maintain strength whereas some are dynamic (changing).

APPLICATION OF ELECTRIC AND MAGNETIC FIELDS

DC MOTORS

  • Current-carrying coils in magnetic fields experience forces causing rotation.
  • Commutators reverse current to allow continuous rotation.

PRACTICAL DC MOTORS

  • Advanced designs allow smoother operation with multiple coils, better torque production and current management.

PARTICLE ACCELERATORS

  • Use magnetic fields to bend paths of accelerated particles.

MASS SPECTROMETERS

  • Measure mass-to-charge ratio of ions using magnetic fields for detection.
  • Assist in determining molecular weights of samples.