Section 2.1: Definition of Electric Field

This section introduces the concept of the electric field, defined as the force per unit charge, and discusses its vector nature and units.

Electric Field Definition:

\( \vec{E} = \frac{\vec{F}}{q} \)

Where \( \vec{F} \) is the force on a test charge \( q \).

Units: N/C (newtons per coulomb)

Example 1

A point charge \( q = +5\mu C \) exerts a force of \( 0.02 \, N \) on a small test charge. Find the electric field at that location.

\( E = \frac{F}{q} = \frac{0.02}{5 \times 10^{-6}} = 4000 \, \text{N/C} \)

Practice Problems

  1. A point charge of \( +8\mu C \) exerts a force of \( 0.04\,N \) on a test charge. Find the electric field.
  2. Compute the electric field at a distance of 0.3 m from a point charge of \( 2\mu C \).
  3. Explain the direction of the electric field due to a negative point charge.
  4. Compare the electric fields at two points equidistant from a charge but in different directions.
  5. Conceptual: Why does the test charge not affect the source charge in the definition of \( \vec{E} \)?
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