Electric Field Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electric Field.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

A region around a charged object where other charges experience a force. Measured in newtons per coulomb (N/C) or volts per meter (V/m).

Every charge creates an invisible 'force zone' around it. Another charge entering this zone feels a push or pull without touching anything.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Fields let charges interact at a distance. The field exists in space even when no test charge is present.

Common stuck point: Field lines point in the direction a positive test charge would move — away from positive, toward negative.

Sense of Study hint: When solving an electric field problem, first identify the source charge Q and the point where you need the field. Then use E = kQ/r^2 to find the magnitude. Finally, determine the direction: the field points away from positive charges and toward negative charges.

Worked Examples

Example 1

medium
What is the electric field 0.5 \text{ m} from a point charge of 4 \times 10^{-6} \text{ C}? Use k = 9 \times 10^9 \text{ N m}^2/\text{C}^2.

Solution

  1. 1
    Electric field from a point charge: E = k\frac{q}{r^2}
  2. 2
    E = 9 \times 10^9 \times \frac{4 \times 10^{-6}}{(0.5)^2} = 9 \times 10^9 \times \frac{4 \times 10^{-6}}{0.25}
  3. 3
    E = 9 \times 10^9 \times 1.6 \times 10^{-5} = 1.44 \times 10^5 \text{ N/C}

Answer

E = 1.44 \times 10^5 \text{ N/C}
The electric field describes the force per unit charge at a point in space. It points radially outward from positive charges and inward toward negative charges.

Example 2

medium
A charge of 2 \times 10^{-9} \text{ C} is placed in an electric field of 5000 \text{ N/C}. What force does it experience?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

hard
Two parallel plates are separated by 0.02 \text{ m} with a potential difference of 100 \text{ V}. What is the electric field between the plates?

Example 2

hard
Two point charges are placed on the x-axis: q_1 = +3 \times 10^{-6} \text{ C} at x = 0 and q_2 = +3 \times 10^{-6} \text{ C} at x = 0.4 \text{ m}. Find the electric field at the midpoint (x = 0.2 \text{ m}). Use k = 9 \times 10^9.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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