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Electric Charges and Fields

Punjab Board · Class 12 · Physics

Flashcards for Electric Charges and Fields — Punjab Board Class 12 Physics. Quick Q&A cards covering key concepts, definitions, and formulas.

45 questions25 flashcards5 concepts

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25 Flashcards
Card 1Coulomb's Law and Charge Distribution

Two identical metallic spheres A and B carry charges of +10 μC and +20 μC respectively. They are made to touch and then separated by 5 cm. Calculate the force between them after separation.

Answer

Step 1: When spheres touch, charge distributes equally. Total charge = +10 + 20 = +30 μC Each sphere gets = 30/2 = +15 μC Step 2: After separation, both have +15 μC r = 5 cm = 0.05 m Step 3: Apply C

Card 2Electric Discharge and Field Strength

Why do you observe a spark when you take off your woolen sweater on a dry day?

Answer

When you pull off a woolen sweater, friction occurs between the wool and synthetic cloth. This friction causes electrons to transfer from one material to another, creating a charge separation. The ch

Card 3Coulomb's Law Fundamentals

State Coulomb's Law in vector form with all symbols explained.

Answer

Coulomb's Law (Vector Form): 𝐅₂₁ = (1/4πε₀) × (q₁q₂/r₂₁²) × 𝐫̂₂₁ Where: - 𝐅₂₁ = Force on charge q₂ due to charge q₁ (in Newtons) - q₁, q₂ = Point charges (in Coulombs) - r₂₁ = Distance between charg

Card 4Superposition Principle and Vector Addition

Three charges of +2 μC, +3 μC, and -2 μC are placed at the vertices of an equilateral triangle of side 10 cm. Calculate the net force on the +3 μC charge.

Answer

Step 1: Setup - Place charges: - q₁ = +2 μC at vertex A - q₂ = +3 μC at vertex B (test charge) - q₃ = -2 μC at vertex C - Side length = 10 cm = 0.1 m Step 2: Force on q₂ due to q₁ (repulsive, along A

Card 5Electric Field Concept and Significance

What is the significance of introducing the concept of electric field instead of using only Coulomb's Law?

Answer

The electric field concept is significant for several reasons: 1. **Independence from Test Charge**: The electric field E = F/q is independent of the test charge placed at a point. It represents a pr

Card 6Electric Field and Motion of Charged Particles

A uniform electric field of magnitude 2000 N/C points in the +x direction. An electron is released from rest at the origin. Calculate its acceleration and the distance it travels in 10 μs.

Answer

Step 1: Find the force on electron Charge on electron: q = -e = -1.6 × 10⁻¹⁹ C Electric field: E = 2000 N/C (in +x direction) Force: F = qE = (-1.6 × 10⁻¹⁹) × (2000) F = -3.2 × 10⁻¹⁶ N (in -x directi

Card 7Gauss's Law and Spherical Symmetry

Why is the electric field zero inside a uniformly charged thin spherical shell? Explain using both Coulomb's Law and Gauss's Law.

Answer

Explanation using Coulomb's Law: Consider a point P inside the shell. Divide the shell into small area elements. Each element dA produces a field at P. Consider two elements on opposite sides of a lin

Card 8Gauss's Law Application - Infinite Wire

Calculate the electric field at a distance of 2 cm from an infinitely long uniformly charged wire carrying a linear charge density of 5 μC/m.

Answer

Given: Linear charge density: λ = 5 μC/m = 5 × 10⁻⁶ C/m Perpendicular distance: r = 2 cm = 0.02 m k = 9 × 10⁹ N·m²/C² For an infinitely long charged wire, using Gauss's Law: Step 1: Apply Gauss's La

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Frequently Asked Questions

What are the important topics in Electric Charges and Fields for Punjab Board Class 12 Physics?
Key topics in Electric Charges and Fields include Chapter 1: Electric Charges and Fields – Complete Concept Map, Electric Charges and Fields – Complete Chapter Overview, Electric Charges and Fields - Concept Hierarchy. These are the concepts Punjab Board Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Electric Charges and Fields — Punjab Board Class 12 Physics?
Understand the core concepts first, then work through the 45 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
How many flashcards are available for Electric Charges and Fields?
There are 25 flashcards for Electric Charges and Fields covering key definitions, formulas, and concepts. Use them daily for 10–15 minutes for best results.

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