Physics Tutorial: Coulomb's Law

Introduction to Coulomb's Law

• Electrical interactions: Non-contact forces that involve charges and distance.
• Key variables: Two charges and the distance between them influence the interaction strength.
• Examples: Plastic golf tube, like-charged balloons, and charged Styrofoam plate.

Force as a Vector Quantity

• Unit: Newton (N), as force has both magnitude and direction.
• Direction: Determined by charge type (like or opposite) and spatial orientation.
• Examples:
  • Like charges (repel): A leftward, B rightward.
  • Opposite charges (attract): C rightward, D leftward.
• Magnitude: Influenced by the charge quantity and separation distance.

Coulomb's Law Equation

• Expression: Electric force is proportional to the product of charges and inversely proportional to the square of the separation distance.
• Formula: ( F = k \frac{Q_1 Q_2}{d^2} )
  • ( Q_1, Q_2 ): Charges in Coulombs.
  • ( d ): Distance in meters.
  • ( k ): Coulomb's constant (~9.0 x 10⁹ N m²/C² in air).
• Point Charges: Coulomb's Law applies when objects behave as point charges.
• Sign of Charges: "+" or "-" indicates excess or shortage of electrons.

Calculations Using Coulomb's Law

• Steps in Problem Solving:
  1. List known variables.
  2. Identify unknown variable.
  3. Substitute values into the equation and solve.
• Example A: Two +1.00 C charges, 1 meter apart, force = 9.0 x 10⁹ N.
• Example B: Two -6.25 nC charges, 61.7 cm apart, force = 9.23 x 10⁻⁷ N.
• Example C: Charges of +3.37 µC and -8.21 µC, force = 0.0626 N, find distance.

Comparing Electrical and Gravitational Forces

• Similarities:
  • Both show inverse square relation with distance.
  • Force proportional to product of cause (charge or mass).
• Differences:
  • Electrical: Can be attractive or repulsive.
  • Gravitational: Always attractive.

Interactive Learning

• Coulomb's Law Interactive: Available in the Physics Interactives section to explore the effect of charge and separation distance on electric force.

Check Your Understanding

• Questions:
  1. Symbol Q represents the charge of a charged object.
  2. Symbol d represents the distance in Coulomb's law equation. 3-7. Various problems involving calculation of electrical force and separation distance.

Conclusion

• Significance of Coulomb's Law: Essential understanding in physics for interactions between charged objects.
• Further Learning: Exploring interactive tools and real-world applications of the concepts.