Device SAC Flashcards
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What it does
The pickup converts string vibrations into electricity and is embedded in the body of the guitar beneath the strings. This creates an electric signal that can be amplified and heard through a speaker.
How it works
The pickups interact with the magnetic guitar strings as they’re played causing a change in flux and generating a current in the coil.
Metallic string
Guitar strings are ferromagnetic which is a property causing them to be magnetically permeable, allowing them to distort the magnetic field of the pickups.
Magnetised screws
Creates a magnetic field (as it’s magnetised by a permanent magnet) which interacts with the string and coils.
Coils
The coils are wrapped around the pickup screws, which has thousands of turns so that when there is a change in flux, a large emf can be generated. The coil is connected by wire to a lead where the sound signal can be transferred to the amplifier.
How is flux involved?
Flux is created by the magnetically permeable string distorting the magnetic field through the nail. Therefore, it moves the magnetic field in the area between the coil loops, creating a change in flux until the string rebounds back to its original position. So, the greater the diameter of the nails, the greater the flux as flux=BA.
How is Faraday’s Law involved?
Faraday’s Law states that when a conductor is placed in a changing magnetic field, an EMF or voltage will be induced (in a closed circuit). So, when the string moves, the magnetic field of the nail changes and therefore, a voltage is generated by the coils. Also, the more loops around the nails, the greater the current generated which is why a guitar coil typically has roughly 5000 turns.
How is Lenz’s Law involved?
Lenz’s Law states that a changing flux generates a current, but the current induced must oppose changes in the initial magnetic field to follow the law of conservation of energy. Therefore, a current will be induced by the string’s movement that opposes the initial magnetic field of the nail. As the string oscillates, the current will flip back and forth, generating an alternating current (AC).
The relationship between input and output voltage and current
The input voltage is generated by the current induced by the string changing the nail’s magnetic field, this input is therefore alternating current and AC voltage because the string oscillates. The output will also be the same which is why there is a converter built into amplifiers to change the AC signal into DC.
Why AC voltages and currents are required
The device cannot create a DC voltage as the pickups operate on a changing flux system which will always generate an AC voltage and changing current.
Lenz’s Law Template
According to Lenz’s law, the induced current must generate a magnetic field that opposes the initial change in flux. As the coil (rotates/moves), the flux (increases/decreases) (to the left/right/into page/out of page). Therefore, from the right hand rule, the induced current must be (clockwise/anticlockwise/left/right).
Note: if initial flux is increasing, induced field must be in the opposite direction. If the initial flux is decreasing, the induced field must be in the same direction.
