Overview
This lecture covers the basics of electromagnetism, explaining how electric currents generate magnetic fields in wires, coils, solenoids, and electromagnets, and how to control and strengthen these fields.
Magnetic Fields from Electric Currents
- Electric currents flowing through a wire create magnetic fields surrounding the wire.
- The magnetic field lines form concentric circles around the wire and are strongest near the wire.
- The direction of the magnetic field depends on the direction of current flow, determined by the right hand rule.
Right Hand Rule
- Point your right thumb in the direction of current; curled fingers show the magnetic field's direction.
- If current direction reverses, the magnetic field direction also reverses.
Coils and Solenoids
- A single loop (coil) of wire with current creates stretched, elliptical magnetic field lines.
- Multiple loops form a solenoid, producing a strong and uniform magnetic field inside.
- Outside, the solenoid's field resembles that of a bar magnet, with defined north and south poles.
Electromagnets
- An electromagnet is created when a current-carrying solenoid produces a magnetic field.
- The magnetic field is present only while current flows; it disappears when current stops.
- Reversing current reverses the direction of the magnetic field and the poles.
Increasing Electromagnet Strength
- Increase current through the solenoid.
- Increase the number of coil turns while keeping solenoid length the same.
- Decrease solenoid length while keeping the number of turns the same.
- Insert an iron core inside the solenoid to induce a stronger magnetic field.
Key Terms & Definitions
- Electromagnetism — The phenomenon where electric currents produce magnetic fields.
- Right Hand Rule — A method to determine magnetic field direction around a current-carrying wire.
- Solenoid — A coil of wire designed to produce a strong, uniform magnetic field.
- Electromagnet — A magnet created by electric current passing through a coil, usually with an iron core.
Action Items / Next Steps
- Review the right hand rule and practice applying it to different circuits.
- List the four ways to increase the strength of an electromagnet.