Req 4a — Build an Electroscope

An electroscope is one of the simplest devices for showing that invisible things can produce measurable effects. Charge the metal part of the device, and the leaves or indicator separate because like charges repel. When ionizing radiation affects the air around the electroscope, the air becomes more conductive, and the stored charge leaks away faster.

What the electroscope is showing

The important idea is not just “the leaves move.” The important idea is why they move.

• A charged electroscope stores electric charge.
• The leaves spread apart because they carry similar charges.
• Ionizing radiation creates ions in the surrounding air.
• Those ions help charge move away, so the electroscope discharges.

That means the nearby radiation is not pushing the leaves directly. It is changing the air so the charge can escape.

If you want a more dramatic visual of radiation, the next classic experiment lets you actually see tracks left behind in vapor.