Overview
This lecture explains how electric current in a wire creates a magnetic field, how a solenoid amplifies this effect, and how to determine magnetic field patterns for wires and solenoids.
Magnetic Fields from Electric Currents
- When current flows through a conducting wire, a magnetic field forms around the wire.
- The strength of the magnetic field increases with a larger current.
- The magnetic field is strongest near the wire and weakens with distance.
- Reversing the direction of current reverses the direction of the magnetic field.
Determining Magnetic Field Direction
- The right hand grip rule helps identify the direction of the magnetic field: thumb points with current, curled fingers show field direction.
- A compass can detect the magnetic field by deflecting when near a current-carrying wire.
Solenoids and Strengthening Magnetic Fields
- Coiling a wire forms a solenoid, which produces a strong, uniform magnetic field inside.
- The magnetic field pattern around a solenoid resembles that of a bar magnet.
- Use the right hand grip rule: fingers curl in the direction of current, thumb points to the solenoid's north pole.
Increasing Magnetic Field Strength in a Solenoid
- Increasing the current raises the magnetic field strength.
- More turns in the coil further strengthen the field.
- Inserting an iron core inside the solenoid enhances the field.
- A solenoid with an iron core is called an electromagnet, which can be switched on and off.
Key Terms & Definitions
- Conventional Current — the direction positive charges would flow, usually from positive to negative terminal.
- Magnetic Field — the region around a magnet or current-carrying wire where magnetic forces are observed.
- Solenoid — a coil of wire designed to strengthen the magnetic effect of the current.
- Right Hand Grip Rule — method using your right hand to find magnetic field direction around a wire.
- Iron Core — a piece of iron inside a solenoid that increases its magnetic field strength.
- Electromagnet — a solenoid with an iron core that acts as a controllable magnet.
Action Items / Next Steps
- Practice drawing the magnetic field patterns for straight wires and solenoids.
- Learn and apply the right hand grip rule for different current directions.
- Memorize the three methods for increasing solenoid magnetic field strength.