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Why do some light bulbs keep glowing even after switching them off ?

Light bulbs that continue to glow after being switched off are often experiencing a phenomenon known as “ghosting” or “residual current.” Several factors contribute to this occurrence:

  1. Capacitive Coupling: In some cases, there may be a capacitive coupling between the wiring in the electrical system and the light bulb. Capacitors can store electrical charge, and even after the switch is turned off, a small amount of current may continue to flow through the circuit, causing the bulb to glow faintly.
  2. Inductive Kickback: Inductive kickback can occur when there is inductive loading in the circuit. This is more common in circuits with inductive loads like motors or transformers. When the switch is turned off, the collapsing magnetic field can induce a brief surge of current, keeping the bulb glowing momentarily.
  3. High-Impedance Circuits: In circuits with high impedance, even a small amount of current can be sufficient to keep the bulb dimly lit after turning it off. High-impedance circuits may result from faulty wiring, poor insulation, or the presence of electronic devices in the vicinity.
  4. Residual Voltage: There may be a residual voltage present in the wiring even when the switch is off. This can happen due to leakage currents, induction from nearby circuits, or poor insulation. The residual voltage may be enough to cause a low-intensity glow in the bulb.

To address the issue of light bulbs continuing to glow after being switched off, it’s essential to investigate the electrical system, check for faulty wiring, and ensure that there are no capacitive or inductive coupling issues. In some cases, the installation of a snubber circuit or the use of a switch with a higher voltage rating can help minimize ghosting effects. Professional assistance may be necessary to identify and rectify specific issues causing the residual glow.

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