Leyden Jars

Van de Graaff generators can produce voltages exceeding 100 kV. While the current is typically limited to microamperes (making it generally safe), the shock can be startling and painful. Students with pacemakers or other electronic medical devices should maintain distance. Always discharge the Leyden jar with a grounded rod rather than your body. The energy stored can exceed 100 mJ in larger jars—sufficient to cause burns if discharged through small contact areas.

The discharge spark produces a loud snap and intense light. Warn the class before discharge to prevent startle reactions. The UV emission from the spark is minimal but repeated close viewing should be avoided. In very dry conditions, ozone production may be noticeable.

Purpose

Demonstrates capacitance and energy storage using a Leyden jar charged by a Van de Graaff generator. Students see charge accumulate and then discharge as a dramatic spark, making stored electrical energy tangible.

Five antique Leyden jars of varying sizes with glass bodies, metal foil linings, wooden stoppers, and metal rods topped with spherical terminals

Modern Leyden jar components on a metal grounding plate: a glass beaker with curved wire electrode ending in a small sphere, and two aluminum cylinders of different sizes; a red banana wire connects to the plate

Assembled modern Leyden jar: aluminum cylinder surrounding the glass beaker on the grounding plate, with the curved wire electrode extending upward from inside the beaker

Figure 1: Antique Leyden jars in various sizes. Each has a glass dielectric separating inner and outer conducting surfaces, with a metal rod and terminal sphere through the stopper.

Figure 2: Modern Leyden jar components: glass beaker (dielectric), curved wire electrode with terminal sphere, two aluminum cylinders (outer conductors), and grounding plate with banana wire connection.

Figure 3: Assembled modern Leyden jar: the aluminum cylinder (outer conductor) surrounds the glass beaker (dielectric) on the grounding plate. The wire electrode (inner conductor) extends up to a terminal sphere for charging.

Large Leyden Jar

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Small Leyden Jar

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Ground Plate

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Danger: High Voltage Hazard

Warning: Spark Intensity Warning

Purpose

Safety Warnings

Danger: High Voltage Hazard

Warning: Spark Intensity Warning

Purpose