Electric field strength

1. Definition of Electric Field Strength

• Electric field strength $(E)$ is the force per unit positive charge at a point in an electric field.
• It is a vector quantity (has both magnitude and direction).

2. Formula for Electric Field Strength

$E = \frac{F}{Q}$

or

$E = k \frac{Q}{r^2}$

where:

• $E =$ Electric field strength $(N·C⁻¹)$
• $F =$ Force $(N)$
• $Q =$ Charge creating the field $(C)$
• $r =$ Distance from the charge $(m)$
• $k =$ Coulomb's constant $(9.0 \times 10^9 N·m²/C²)$

3. Understanding Electric Field Strength

✔ A strong electric field has a greater force on charges.

✔ Field strength decreases as distance increases.

✔ Direction of the field is away from positive charges and towards negative charges.

4. Using Electric Field Strength

5. Key Takeaways

✔ Electric field strength is force per unit charge.

✔ Field strength decreases with distance.

✔ Multiple charges require vector addition to find the resultant field.

✔ Always convert distances to metres when using the formula.

Exam Tip

💡 When solving problems, check the direction of the electric field before calculating the resultant field!