4.2.1 Electric charge (3)
Resources |
Revision Questions |
Physics
Login to see all questions
Click on a question to view the answer
1.
Question 2
A student carries out an experiment to investigate the production of electrostatic charges by friction. They rub a glass rod with silk cloth and then bring it near small pieces of paper. Describe the expected observations and explain why these observations occur in terms of the transfer of electrons.
Expected Observations: The small pieces of paper will be attracted towards the glass rod. The degree of attraction will depend on how vigorously the rod was rubbed and the type of cloth used.
Explanation: When the glass rod is rubbed with silk cloth, electrons are transferred from the silk to the glass. This transfer results in the glass rod acquiring a net negative charge. The negatively charged glass rod then creates an electric field around it. The small pieces of paper, being neutral, have an equal number of positive and negative charges. Due to the electric field created by the negatively charged glass rod, the positive charges within the paper are attracted towards the rod, resulting in the paper being pulled towards it. This is a direct consequence of the electrostatic force between oppositely charged objects.
2.
A diagram shows two charges, Q1 and Q2. Q1 has a charge of +2.0 x 10-6 C and Q2 has a charge of -3.0 x 10-6 C. The distance between the charges is 0.1 m.
State the nature of the electrostatic force between Q1 and Q2. Explain your answer in terms of the charges involved.
Answer: The electrostatic force between Q1 and Q2 is attractive.
Explanation: Q1 has a positive charge (+2.0 x 10-6 C) and Q2 has a negative charge (-3.0 x 10-6 C). Opposite charges attract.
The positive charge of Q1 creates an electric field that points towards the negative charge of Q2. Similarly, the negative charge of Q2 creates an electric field that points towards the positive charge of Q1. These electric fields link the charges, resulting in an attractive force between them.
3.
Describe an experiment to demonstrate the charging of a solid by friction. In your description, clearly state the materials you would use, the procedure you would follow, and how you would observe the charging effect. Explain what observations would support the statement that only negative charge is transferred.
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:
- Rub the plastic ruler vigorously against the wool for several minutes.
- Bring the rubbed ruler close to the small, lightweight objects (paper clips, foil).
- 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.