Class 12th Physics-Electric Charges and Fields – Properties of Charges – like and Unlike part-4.

15 ELECTRIC CHARGE AND ELECTRIC FIELD

In Class 12 Physics, Chapter 1—Electric Charges and Fields, a fundamental concept is the properties of electric charges, particularly the behavior of like and unlike charges. This principle is crucial for understanding electrostatic interactions and forms the basis for many applications in physics and engineering.

Fundamental Property: Like Charges Repel, Unlike Charges Attract

Experimental observations have established that:

• Like charges (both positive or both negative) repel each other.

• Unlike charges (one positive and one negative) attract each other.

This behavior is a cornerstone of electrostatics and is consistently observed in various experiments.

Illustrative Examples

1. Glass Rod and Silk Cloth:

   • When a glass rod is rubbed with silk, the rod becomes positively charged, and the silk acquires a negative charge.

   • Bringing two similarly charged glass rods close to each other results in repulsion.

2. Plastic Rod and Wool:

   • Rubbing a plastic rod with wool imparts a negative charge to the rod and a positive charge to the wool.

   • Two such negatively charged plastic rods will repel each other, while a negatively charged plastic rod and a positively charged glass rod will attract each other.

These observations led to the classification of charges as positive and negative, a convention introduced by Benjamin Franklin. By this convention, the charge acquired by a glass rod when rubbed with silk is considered positive, and the charge acquired by the silk is negative.

Scientific Explanation

The interaction between electric charges is governed by Coulomb’s Law, which states that the electrostatic force ($F$) between two point charges is directly proportional to the product of the magnitudes of the charges (q1q_1q1​ and q2q_2q2​) and inversely proportional to the square of the distance ($r$) between them:

F=k∣q1⋅q2∣r2F = k \frac{{|q_1 \cdot q_2|}}{r^2}F=kr2∣q1​⋅q2​∣​

Where:

• $F$ is the magnitude of the electrostatic force,

• q1q_1q1​ and q2q_2q2​ are the amounts of the charges,

• $r$ is the distance between the centers of the two charges,

• $k$ is Coulomb’s constant (8.9875×109 N\cdotpm2/C28.9875 \times 10^9 \, \text{N·m}^2/\text{C}^28.9875×109N\cdotpm2/C2).

According to this law:

• If q1q_1q1​ and q2q_2q2​ have the same sign (both positive or both negative), the force is repulsive.

• If q1q_1q1​ and q2q_2q2​ have opposite signs, the force is attractive.

This quantitative relationship explains the observed behaviors of like charges repelling and unlike charges attracting.

Key Takeaways

• Polarity of Charge: The property that differentiates positive and negative charges, leading to their respective behaviors of attraction and repulsion.

• Charge Interaction: Like charges repel; unlike charges attract.

• Coulomb’s Law: Provides the mathematical framework to calculate the electrostatic force between two charges.

Understanding these principles is essential for delving deeper into topics like electric fields, potential, and capacitance in the study of electromagnetism.

If you have further questions or need clarification on related topics, feel free to ask!

Class 12th Physics-Electric Charges and Fields – Properties of Charges – like and Unlike part-4.

Electric Charges, Forces and Fields

ELECTROSTATICS – I