Overview
This lecture explains how electric currents create magnetic fields, focusing on wires, coils, solenoids, and electromagnets, and discusses ways to increase electromagnet strength.
Electromagnetic Fields in Wires
- Electric currents in wires produce magnetic fields represented by concentric circles around the wire.
- The magnetic field is strongest closest to the wire.
- The direction of the magnetic field depends on the current’s direction and can be determined using the right hand rule.
- Reversing the current reverses the direction of the magnetic field.
Magnetic Fields in Coils and Solenoids
- A single loop or coil of wire with current stretches the magnetic field into ellipses; the field combines to run straight through the center.
- Adding more turns to a coil creates a solenoid, which produces a strong, uniform magnetic field inside.
- The magnetic field outside a solenoid resembles that of a bar magnet, with a defined north and south pole.
Electromagnets and Field Control
- An electromagnet is created when a current-carrying solenoid acts like a magnet.
- Electromagnets are only magnetic when current flows; turning off the current removes the magnetic field.
- Reversing the direction of the current reverses the magnetic field and the poles of the electromagnet.
Increasing Electromagnet Strength
- Increase the current flowing through the solenoid.
- Increase the number of coil turns while keeping solenoid length the same.
- Decrease the length of the solenoid while keeping the number of turns the same.
- Insert an iron core, which becomes an induced magnet and greatly increases magnetic field strength.
Key Terms & Definitions
- Electromagnetism — The phenomenon where electric currents produce magnetic fields.
- Right hand rule — A method to determine the direction of a magnetic field around a current-carrying wire.
- Solenoid — A coil of wire with many turns that generates a strong, uniform magnetic field when current flows.
- Electromagnet — A type of magnet whose magnetic field is produced by electric current.
- Iron core — A soft magnetic material inserted into a solenoid to increase magnetic field strength.
Action Items / Next Steps
- Review the right hand rule and practice determining magnetic field directions.
- Memorize the four ways to strengthen an electromagnet.