Electric Fields Study Guide

Study Guide: Electric Charge and Electric Fields

Lecture 1: Introduction to Electric Effects

- Electric Force: Acts between charged particles; like charges repel, opposite charges attract.
- Conservation of Charge: Charge can transfer but the total remains constant.
- Quantization of Charge: q = Ne, where N is an integer and e = 1.602 10 C
- Types of Materials:
Conductors: Free-moving electrons (e.g., metals)
Insulators: Electrons bound to atoms (e.g., rubber)
Semiconductors: Intermediate (e.g., silicon)

Coulombs Law:
F = k |q q| / r, where k = 8.99 10 Nm/C

Vector Form:
F=kqq/r
Direction: Along the line joining charges; attractive or repulsive.


Lecture 2: Electric Field (Part 1)

Electric Field Definition:
E = F / q or F = qE
A field is created by a source charge and felt by a test charge.

Electric Field of a Point Charge:
E=kq/r
- Away from q if q > 0
- Toward q if q < 0

Field Line Properties:
1. Start on + charges, end on -
2. Never cross
3. Denser lines stronger field
4. Proportional to charge magnitude

Examples:
- Three-Point Charges in Triangle: Use vector components.
- Electric Field at Midpoint: Superposition.
- Equilibrium Point: Net force = 0 field = 0
- Uniform Electric Fields: Constant field between plates.


Lecture 3: Electric Field (Part 2)

Force in a Uniform Electric Field:
Kinematics: a = qE/m, v_f = (2aqd/m)
Work-Energy: W = Fd = mv v = (2qEd/m)

Examples:
- Water Droplet Suspended: q = mg/E (opposite to field direction)
- Electron Deflection: Use projectile motion equations