Lecture on Electric Fields

Introduction to Electric Field

• New concept: Electric field.
• Charge Notation: Capital Q (source charge), little q (test charge).
• Coulomb's Law: F = (q * Q * Coulomb's constant) / R^2.
• If both charges are positive, they repel; if opposite, they attract.

Definition of Electric Field

• Symbol: E.
• At location P, E = Force experienced by test charge / test charge.
• Vector Quantity: Direction depends on charge polarity.
• Convention: E field direction is that of force on a positive test charge.
• Unit: Newtons per Coulomb (N/C).

Graphical Representation

• Arrows indicating direction and magnitude of electric field.
• Stronger field closer to charge (inverse square law).

Electric Field with Multiple Charges

• Superposition Principle: Net E field is vector sum of individual fields.
• Example with charges Q1, Q2, Q3, etc.
• Net E field at a point: Sum of E vectors from all charges.
• E field direction and magnitude calculation.

E Field with Opposite Charges

• Plus (3) and Minus (1):
  • Near minus, the field points towards it.
  • Far away, behaves like a combined charge (net positive) due to inverse R^2.
  • Transition point where E field is zero; assignment to find this.

Field Lines Representation

• Tangential force direction for a positive test charge.
• Field line density indicates field strength.
• Field Lines in Dipole and Equal Charges:
  • In a dipole, lines are symmetric.
  • Opposite charges have no net E field far away.

Creating a Dipole

• Experiment: Spheres induced with charges.
• Demonstrated charge polarity using an electroscope.
• Dipole in Electric Field:
  • Torque causes rotation to align with field lines.

Visualization of Field Configurations

• Using grass seeds in oil to show field lines.
• Different configurations for dipoles and same polarity charges.

Demonstration with VandeGraaff Generator

• Interaction of a charged balloon and field from the generator.
• Balloon demonstrates field interaction by bouncing between points.

Conclusion

• Explored visualization and concepts of electric fields through various demonstrations and theoretical discussions.
• Homework assignments to reinforce understanding of dipoles and superposition.