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What Parts Do Magnets Play in a Radio?

Electricity and magnetism are two aspects of the same phenomenon. Any electrical field generates a magnetic field, and vice versa. These properties can be exploited to control current flow and sound production in an electric circuit. In circuits, the inductor is a component of coiled wire that functions as an electromagnet. Furthermore, some circuits use permanent magnets. In a radio, magnetism is used in two ways. First, the speaker of the radio uses both an inductor and a permanent magnet. Second, the tuning portion of the radio relies on inductors.

Induction
- Inductors are components that consist of a segment of coiled wire. As current flows through the coils of the wire, a magnetic field is generated in the core of the inductor. This magnetic field opposes the flow of current through the inductor. The magnetic field grows in strength until the flow of current reaches a constant level based on the inductance value of the inductor. When current ceases to flow through the inductor, the magnetic field releases energy, which creates a current that continues to flow in the direction of the initial current.
Magnets in Speakers
- Two magnets control the output of the speaker portion of a radio. An inductor responds to the electronic waveform signal. The current of this signal changes rapidly. As this happens, the inductor's magnetic field changes rapidly. The inductor is close to a second, permanent magnet. Because the inductor has a rapidly-changing magnetic field, it is alternately attracted to and repelled from the permanent magnet. This physical movement then translates into a movement of air, which we experience as sound.
The Tuning Circuit
- Inductors play an important role in the tuning portion of a radio. In conjunction with a capacitor, the inductor helps create a resonant body that responds only to a specific frequency. As a capacitor experiences electric current, it builds voltage across its plates. When that current source disappears, the capacitor discharges that voltage, and current flows in the opposite direction. When coupled with an inductor in parallel, this creates an oscillation of current at a specific frequency. If the components were perfect, this oscillation would continue forever. However, energy is dissipated in the internal resistance of the components.
Adjusting the Tuning of the Radio
- The resonant frequency of the inductor-capacitor network is obtained by taking the inverse of the product of the square root of the inductance and capacitance and two times pi. Therefore, varying either the inductance or capacitance will change the resonant frequency. Variable capacitors are commonly used as the tuning mechanism in radios. Once a tuning frequency has been obtained, the tuning circuit will respond only to oscillating signals from the antenna at that frequency.

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