Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges

4.2.1 Electric Charge

Producing Electrostatic Charges by Friction

When two different materials rub together, electrons move from one material to the other. The material that loses electrons becomes positively charged, while the material that gains electrons becomes negatively charged. This is called frictional charging.

  1. Take a glass rod and a silk cloth. Rub the rod with the cloth for about 30 seconds.

  2. Hold the rod near a small piece of paper. If the paper is attracted, the rod has a negative charge.

  3. Repeat the experiment with a rubber rod and a wool cloth. The rubber rod will become positively charged.

⚡️ Analogy: Think of electrons as tiny “water droplets” that can hop from one surface to another when they’re shaken together, just like water splashes from one cup to another when you stir them together.

Detecting Electrostatic Charges

You can detect static charges using simple tools that show how charges attract or repel.

  • Paper test: Hold a small piece of paper near a charged rod. If it moves, the rod is charged.

  • Balloon test: Rub a balloon on your hair and then hold it near a wall. The balloon will stick if it has a charge.

  • Metal sphere: Touch a metal sphere to a charged rod. The sphere will acquire the same charge and can be used to test other objects.

🔋 Tip: The closer the charged object is to the detector, the stronger the effect. Keep a safe distance to avoid accidental sparks.

MaterialTendencyResult
Glass + SilkGlass loses electronsGlass becomes negative
Rubber + WoolRubber gains electronsRubber becomes positive

Examination Tips

• Remember that charge is conserved; the total charge before and after friction remains the same.

• Use the sign of charge (positive or negative) to predict attraction or repulsion.

• When describing an experiment, include the materials used, the method, and the observations.

• In multiple‑choice questions, look for the correct pairing of material and charge in the table.

• Practice drawing a simple diagram: show the two objects, the direction of electron transfer, and the resulting charges.