Electric Field Strength and Potential

Overview

This lesson connects field strength and energy ideas for point charges. You will use the point-charge field strength equation, define electric potential, link field strength to potential gradient, and calculate electric potential energy for two point charges.

What You Need to Know

• The electric field strength due to a point charge follows an inverse-square relationship with distance.
• Use electric potential to compare energy changes per unit positive charge between points in a field.
• Electric potential can be positive or negative depending on the sign of the source charge.
• The electric field at a point is equal to the negative of the potential gradient at that point.
• Electric potential energy depends on both charges and their separation.
• Electric potential and electric potential energy are scalar quantities, but force and field strength require direction.

How to Work Through It

1. Start by deriving or comparing point-charge field strength with Coulomb’s law.
2. Define electric potential using work done per unit positive charge.
3. Use potential-distance graphs to identify the sign and gradient of the field.
4. Practise calculations involving field strength, potential, and potential energy.

Check Your Understanding

• How does field strength change when distance from a point charge doubles?
• Why does electric potential have a sign?
• What does the negative potential gradient tell you about the electric field?
• How is electric potential energy different from electric potential?

Common Mistakes

• Confusing electric potential with electric potential energy.
• Dropping the sign of Q when using electric potential.
• Treating potential gradient as just a graph steepness without linking it to field direction.
• Using the point-charge equations for a uniform field between plates.

Next Steps

• Practise selecting between uniform-field and point-charge equations.
• Bring electric and gravitational field comparisons into the practice lesson.