Overview
This lecture reviews Hans Christian Ørsted’s experiments on the effects of electric current on a magnetic compass needle, examining the setup, possible explanations, and material variations.
Ørsted's First Experiment
- Ørsted used a battery connected to a wire (the "uniting wire") aligned north-south above a compass.
- When current flowed through the wire, the compass needle deflected westward, indicating an effect from the electric current.
Investigating the Cause of Deflection
- Ørsted considered if the observed deflection could be explained by Coulomb's law (attraction/repulsion of charges).
- He hypothesized the wire might carry an overall positive charge, affecting a charged compass needle.
- When the wire was moved east or west of the needle, the direction of deflection did not change as would be expected under Coulomb's law.
- Concluded that Coulomb attraction and repulsion could not explain the compass needle’s movement.
Material Variations and Further Observations
- Ørsted repeated the experiment with wires made of platinum, gold, silver, iron, brass, and zinc.
- The compass needle still deflected regardless of wire material, though the effect was weaker with some metals.
- Inserting a cup of water between connections still allowed the compass to deflect if the wires in water were close together.
- The strength of the effect depended on the electrical conductivity of the materials used.
Key Terms & Definitions
- Galvanic Cell — an early battery producing electrical current from chemical reactions.
- Uniting Wire — the wire conducting current above the compass in Ørsted’s experiments.
- Coulomb's Law — law stating like charges repel and opposite charges attract.
- Conductivity — a material’s ability to allow electric current to pass through it.
- Declination — the turning or deflection of the compass needle from its original direction.
Action Items / Next Steps
- Review the relationship between electric potential (voltage), current, and resistance for the next lecture.