The foil electroscope is a classic, portable, and highly sensitive electrostatic detection and teaching demonstration instrument. By changing the angle of two extremely thin metal foils, it intuitively displays whether an object is charged, the positive and negative electrical properties, and the relative size of the charge. It is suitable for physics laboratories and general facilities in middle schools and universities. Typical experiment: Friction electrification demonstration (glass rod/rubber rod); Static induction and conductor grounding experiment; Static shielding verification; Qualitative observation of the relationship between Coulomb force magnitude and distance; High voltage generator output polarity judgment.