One way the student could improve the reliability of their results is to repeat the experiment multiple times for each material. This is because a single trial might be affected by random errors, such as a poor connection between the wires and the battery, or a slight variation in the bulb's brightness.

By repeating the experiment several times (e.g., 3 or 5 times) for each material and calculating the percentage of times the bulb lit up, the student can obtain a more accurate and reliable result. The average percentage of successful trials would then provide a better indication of whether a material is a conductor or an insulator. This reduces the impact of random errors and provides a more robust conclusion.

Experiment: Detection of Electrostatic Charges using a Charged Sphere and a Metal Plate

Diagram:

Apparatus:

• A charged sphere (e.g., a polystyrene ball rubbed with wool).
• A negatively charged metal plate (e.g., a piece of metal rubbed with cloth).
• A lightweight object (e.g., a cork or a small piece of paper).

Procedure:

1. Bring the charged sphere close to the negatively charged metal plate, but without touching it.
2. Observe the behaviour of the lightweight object placed near the sphere and the plate.

Expected Results: The lightweight object (cork or paper) will be attracted towards the negatively charged metal plate. It will also be attracted towards the charged sphere, although the attraction might be weaker.

Explanation: The negatively charged metal plate creates an electric field. The charged sphere also creates an electric field. The lightweight object, being neutral, experiences forces due to both electric fields. The electric field from the negatively charged plate attracts the positive charges in the lightweight object towards the plate. The electric field from the charged sphere attracts the negative charges in the lightweight object towards the sphere. The net effect is that the lightweight object is pulled towards the negatively charged plate. The apparatus is designed this way to clearly demonstrate the interaction between a charged object and a charged plate, and to show the attraction of a neutral object to both.

Experiment: Demonstrating Charging by Friction

Materials: A plastic ruler, a piece of wool, small pieces of cork, and a collection of small, lightweight objects (e.g., paper clips, small pieces of foil).

Procedure:

1. Rub the plastic ruler vigorously against the wool for several minutes.
2. Bring the rubbed ruler close to the small, lightweight objects (paper clips, foil).
3. Observe the objects for any attraction to the ruler.

Observations: The small, lightweight objects will be attracted to the plastic ruler. This attraction is due to the electrostatic force between the charged objects. The objects are attracted because they have been given a net negative charge by the transfer of electrons from the plastic ruler.

Supporting Evidence for Negative Charge Transfer: The objects are attracted to the plastic ruler, which has been shown to gain electrons from the wool. This indicates that the ruler has acquired a net negative charge. Since the transfer involves only electrons, and electrons are negatively charged, this confirms that only negative charge is transferred during the friction process. If positive charge were also transferred, the objects would be repelled by the ruler.