Electromagnetism Lecture Notes

Introduction to Electromagnetism

• Electromagnetism is the phenomenon whereby electric currents produce their own magnetic fields.
• We will explore how this works in:
  • Ordinary wires
  • Coils
  • Solenoids
  • Electromagnets

Magnetic Fields in Wires

• Concept: Electric current in a wire produces a magnetic field around it.
• Field Lines: Represented by concentric circles around the wire.
  • Closest near the wire where the magnetic field is strongest.
• Right Hand Rule:
  • Thumb points in the direction of the current.
  • Fingers curl in the direction of the magnetic field.
  • Example: Current flowing upwards results in an anti-clockwise magnetic field.

Magnetic Fields in Coils

• Single Flat Circular Coil:
  • Current flows in through the bottom left and out through the right.
  • Magnetic fields stretch out and form ellipses, combining to form a single magnetic field through the center.
• Adding More Turns:
  • Creates a solenoid with a strong and uniform magnetic field inside.

Solenoids and Electromagnets

• Solenoid:
  • Acts like a bar magnet with a north and south pole.
  • Magnetic field is strong and uniform inside;
  • Outside field resembles that of a bar magnet.
• Electromagnet:
  • Created by running current through a solenoid.
  • Magnetic only when current flows; can be turned on and off.
  • Magnetic field direction can be reversed by reversing current direction.

Enhancing Electromagnet Strength

• Ways to Increase Strength:
  1. Increase current through the solenoid.
  2. Increase the number of turns in the coil (keeping solenoid length same).
  3. Decrease the length of the solenoid (keeping number of turns same).
  4. Add an iron core inside the solenoid—induces magnetism and increases field strength.
• Iron Core:
  • Soft magnetic material that becomes an induced magnet when solenoid is on.
  • Loses magnetic field when current is off.

Conclusion

• Electromagnets provide controllable magnetic fields with adjustable strength and direction.
• Important to understand ways to manipulate and enhance these fields for practical applications.