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An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical hand-made instruments to high-precision electronic devices. Modern electrometers based on vacuum tube or solid state technology can be used to measure extremely small currents down to 1 femtoampere. A simpler but related instrument, the electroscope, works on similar principles but indicates only the relative magnitudes of voltages or charges.

Simple charge indicating device

The gold-leaf electroscope was one of the first instruments to indicate electric charge. It is still used for science demonstrations but has been superseded in most applications by electronic measuring instruments. Reconditioned Premier DR® LEAF and LAWN VACUUM. The instrument consists of two thin leaves of foil suspended from an electrode. When the electrode is charged by induction or by contact, the leaves acquire similar electric charges and repel each other due to the Coulomb force. Their separation is a direct indication of the net charge stored on them. The leaves may be enclosed in a glass envelope to protect them from draughts, and the envelope may be evacuated to minimize charge leakage. A further cause of charge leakage is ionizing radiation, so to prevent this, the electrometer must be surrounded by lead shielding.