Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.4.2Atoms, Elements and Compounds

Core Practical- Investigating Charging by Friction — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 24 of 26 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Section 1 of 5Variables and Equipment

2.4.2 Core Practical- Investigating Charging by Friction
Variables and Equipment
Independent variable
  • The material of the rod that is rubbed with a cloth and brought near the polythene rod.
Dependent variable
  • The motion of the suspended polythene rod, shown as attraction, repulsion or no movement.
Control variables
  • The rubbing time, the type of cloth and the length of the rods must be kept the same for every test.
Equipment
  • A polythene rod and rods of acrylic, acetate, glass and wood, with cloths, a cradle, nylon string and a wooden stand.

Section 2 of 5Method

1
Hold a polythene rod at its centre and rub both ends with a cloth to charge it.
2
Suspend the rod from the cradle on nylon string so that it can swing freely without touching the ends.
3
Rub a second rod of a different material with its own cloth, and bring one end near the end of the polythene rod without touching it.
4
Record whether the polythene rod moves towards, away from, or stays still in response, then repeat with each material.
5
If the ends touch, the charge leaks away and the forces disappear, so the test must be repeated with a freshly charged rod.

Section 3 of 5Analysing the Results

The direction of motion of each rod shows whether the two charges are the same or opposite.

Polythene
  • Rubbing gives electrons to the polythene, so it becomes negatively charged.
Acetate
  • Rubbing takes electrons away from the acetate, so it becomes positively charged.
Attraction
  • A rod that moves towards the polythene rod has the opposite charge to the polythene.
Repulsion
  • A rod that moves away from the polythene rod has the same charge as the polythene.

Section 4 of 5Worked Example

Question

  • A charged polythene rod is suspended.
  • An acetate rod is rubbed and brought near, and the polythene rod turns towards it.
  • What can be concluded about the charges?

  1. Attraction means the two rods have opposite charges.
  2. Polythene is charged negatively by rubbing, because it gains electrons from the cloth.
  3. Therefore the acetate rod must be positively charged, because it has lost electrons.

Answer The polythene rod is negative and the acetate rod is positive, so the rods have opposite charges.

Section 5 of 5Exam Checklist & Tips

2.4.2 – Key Points for the Exam

  • Charging by friction Charge transferred between two insulators when they are rubbed together, by electrons moving from one to the other.
  • Polythene An insulating plastic that becomes negatively charged when it is rubbed with a cloth.
  • Attraction A force that pulls two objects together, shown by charged objects with opposite charges.
  • Repulsion A force that pushes two objects apart, shown by charged objects with the same charge.
  • Discharge The loss of charge from an object, which happens when a charged object touches another object.

Common Mistakes

  • Stating that protons move during charging by friction; only electrons transfer between the materials.
  • Allowing the two charged ends to touch, which discharges the rods and removes the forces.
  • Changing the rubbing time between tests, which alters a control variable and makes the results unreliable.
  • Concluding that a rod is charged just because it moves, without comparing its behaviour with the polythene rod.

Last updated:

\n