Course Focus: Transition from electricity to magnetism.
Historical Context: 5th century B.C. Greeks discovered magnetite, an iron oxide found in Magnesia, responsible for magnetic properties.
Properties of Magnetite
Poles of Magnet: Magnetite has two poles, labeled A (North) and B (South).
Like poles repel (A & A, B & B) and opposite poles attract (A & B).
Monopoles: Isolated magnetic poles (monopoles) do not exist; magnetic dipoles are always in pairs.
Historical Discoveries
Gilbert's Experiment (16th century): Established that Earth acts as a giant magnet.
Oersted's Discovery (1819): Found that electric current creates a magnetic field, linking electricity and magnetism.
Magnetic Fields and Currents
Magnetic Field Direction: Current direction affects magnetic field orientation, determined by the right-hand corkscrew rule.
Current into the board: cross (X).
Current out of the board: dot (•).
Demonstration of Magnetic Fields
Experiment with Current: High current (300 A) alters compass needle direction, demonstrating magnetic field response.
Force on Current-Carrying Wire: Magnetic fields exert forces on current-carrying wires, described by the relation I cross B, where I is current and B is the magnetic field.
Interactions Between Wires
Same Direction Currents: Wires attract each other when currents flow in the same direction.
Opposite Direction Currents: Wires repel each other when currents flow in opposite directions.
Demonstration: Showed two current-carrying wires attracting and repelling using a simple setup.
Magnetic Fields vs. Electric Fields
Conductor vs. Electric Field: Conductors affect electric fields significantly, while magnetic fields remain unaffected by conductors.
Defining Magnetic Field Strength: Magnetic field strength defined using the Lorenz force, which involves moving charges.
Formula: F = q * v * B (where F is the magnetic force, q is charge, v is velocity, and B is the magnetic field).
Units of Magnetic Field
Tesla (T): SI unit for magnetic field strength; 1 Tesla = 10,000 Gauss.
Earth's Magnetic Field: Approximately 0.5 Gauss, while strong magnets can reach kilogauss levels.
Applications in Technology
Television Distortion: Interaction of magnetic fields with electron beams in TVs distorts images.
Magnetic Effects on Electric Charges: Magnetic fields can modify the direction of moving charges but cannot do work on them (no change in kinetic energy).
Current in Wires
Force Calculation: Force on a current-carrying wire in a magnetic field can be calculated by integrating over the length of the wire.
Example Calculation: A wire carrying 300 A in a magnetic field of 0.2 T experiences a force of approximately 6 Newtons.
Motor Contest Introduction
Objective: Build a motor using provided materials (wire, magnets, etc.) to achieve the highest RPM.
Concept of a Motor: Current loop in a magnetic field generates torque; design must allow for continuous motion without tangling wires.
Commutator Design: Reverses current direction at pivotal points to maintain consistent torque direction.
Motor Demonstration
Current Loop Experiment: Demonstrated changing current in a loop under a magnetic field to illustrate torque and motion.
Torque Reversal: Explained how a commutator solves the torque reversal problem when current changes direction.
Conclusion
Importance of Understanding: Emphasized the connection between magnetism and electricity and the practical applications in building motors.
Encouragement for Contest Participation: Promoted engagement with practical physics through the motor-building challenge.