Magnetic Force

Lecture 19 – Learning Outcomes

  • Understand magnetic forces and fields by:

    • Distinguishing between magnetic poles and electric charges

    • Calculating forces on electric charges or currents in magnetic fields

    • Using the right-hand rule to find the direction of magnetic forces

Lecture and Lab Feedback

  • Midterm 3 is graded, results handed back next Monday

  • Grade update forthcoming (including 1 dropped midterm)

  • Discussion of final exam and last chances to turn in work scheduled for Wednesday

Introduction to Magnetic Fields

  • Electric fields were studied previously; magnetic fields are more complex

  • Magnetic fields are generated by magnetic poles (North and South)

  • Field lines: from North (N) to South (S)

  • Magnetic poles always exist as pairs, unlike electric charges

  • Electric charge signs do not correspond to magnetic pole types

Magnetic Force

  • Magnetic fields exert forces on charges, similar to electric fields

  • Formula for magnetic force:[ F_{magnetic} = q v B \sin(\theta) ]

    • Fast-moving charges feel a stronger force

    • Charges moving parallel to the field experience no force

  • Relevant equations:

    • Electric force: [ F_{electric} = qE ]

    • For current: [ F_{magnetic} = LI B \sin(\theta) ]

Direction of Magnetic Force

  • Magnetic force is a vector quantity; direction determines its effect

  • Utilize the right-hand rule:

    • Middle finger: direction of magnetic field (B)

    • Index finger: velocity of charge (v)

    • Thumb: direction of magnetic force ( F_{magnetic} )

  • Forces are always perpendicular to both velocity and magnetic field

Magnetic Force on Wires

  • Wires with current feel magnetic forces: [ F_{magnetic} = L I B \sin(\theta) ]

  • Right-hand rule applies similarly:

    • Middle finger: direction of B

    • Index finger: direction of positive current (I)

    • Thumb: direction of ( F_{magnetic} )

Checkpoint Questions & Discussions

  • Questions on orientations of magnetic forces and student discussions on magnetic force concepts

  • Students encouraged to apply the right-hand rule to resolve discussions

  • Additional emphasis on real-world applications and feedback during worksheets

Additional Practice

  • Practice questions provided in worksheet format, offering group work opportunities

  • Reinforcement of key formulas and the right-hand rule in practical scenarios