A proof plane is a simple tool used to transfer charge from one object to another, typically from an electrostatically charged object to an electroscope or other measuring device.

Features:

1. Metallic Construction: Proof planes are usually made of a conductive metal like brass or aluminum, allowing them to easily conduct electric charge.
2. Flat Shape: The proof plane typically has a flat shape, which helps in efficiently collecting and transferring charge from charged objects.
3. Small Size: It’s designed to be small enough to fit into tight spaces or to make precise contact with charged objects.
4. Handle: Some proof planes have a handle or insulating grip to allow for safe and easy handling by experimenters.
5. Smooth Surface: The surface of the proof plane is usually smooth to ensure efficient transfer of charge without loss or leakage.
6. Non-reactive: The material used in making proof planes is non-reactive, ensuring that it doesn’t interfere with the charges being transferred during experiments.
7. Versatility: Proof planes are versatile tools used in various electrostatic experiments, including demonstrations of charging by induction, testing the presence of charge on objects, and determining the magnitude and sign of charges.
8. Affordability: They are relatively inexpensive and widely available in science supply stores or online retailers, making them accessible to educators, students, and researchers.

Overall, proof planes play a crucial role in electrostatic experiments by allowing researchers to manipulate and measure electric charge accurately and reliably.