An electric guitar starts with vibrating metal strings, but most of the sound people hear comes from electricity and speakers. When a string is plucked, it vibrates at certain frequencies that determine the pitch. Magnetic pickups under the strings turn those vibrations into a changing electrical signal.
An amplifier then strengthens the signal enough to move a speaker cone and fill a room with sound.
A pickup contains magnets wrapped in many turns of copper wire, forming a coil. The steel string disturbs the pickup's magnetic field as it moves, which induces a small voltage in the coil. This changing voltage carries the same timing pattern as the string vibration, so the amplifier can boost it without changing the basic note.
The speaker converts the amplified electrical signal back into pressure waves in the air that our ears detect as music.
Key Facts
- Frequency controls pitch: higher frequency means higher pitch.
- For a vibrating string, f = v / (2L), where L is string length and v is wave speed on the string.
- Wave speed on a string depends on tension and mass density: v = sqrt(T / μ).
- A magnetic pickup uses electromagnetic induction to turn string motion into voltage.
- Faraday's law: induced voltage increases when magnetic flux changes faster.
- An amplifier increases signal power so a speaker can move air and create louder sound.
Vocabulary
- Pickup
- A pickup is a device with magnets and coils that converts a vibrating metal guitar string into an electrical signal.
- Electromagnetic induction
- Electromagnetic induction is the production of voltage when a magnetic field through a coil changes.
- Amplifier
- An amplifier is an electronic device that increases the strength and power of an electrical audio signal.
- Frequency
- Frequency is the number of vibrations or cycles per second, measured in hertz.
- Speaker cone
- A speaker cone is a moving surface that pushes and pulls air to create sound waves.
Common Mistakes to Avoid
- Thinking the pickup is a microphone, which is wrong because most electric guitar pickups sense metal string motion through magnetism rather than directly sensing air pressure.
- Assuming the amplifier creates the note, which is wrong because the vibrating string sets the frequency while the amplifier mainly increases the signal's power.
- Ignoring string tension, which is wrong because increasing tension increases wave speed and raises the pitch of a string.
- Confusing louder with higher pitch, which is wrong because loudness depends mainly on vibration amplitude and amplifier power, while pitch depends mainly on frequency.
Practice Questions
- 1 A guitar string vibrates at 440 Hz. What is the period of one vibration in seconds?
- 2 A string has a wave speed of 120 m/s and a vibrating length of 0.75 m. Using f = v / (2L), find its fundamental frequency.
- 3 A guitarist moves from a clean amplifier setting to a more powerful setting without changing the fretted note. Explain what changes in the sound and what stays mostly the same.