Electric Field
Force per unit charge at a point.
Formula
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How it works
An electric field tells you how strongly a region of space pushes or pulls on a charged object. The formula E = F/q says that if you place a small positive test charge at a point, the force it feels divided by the size of that charge gives the field strength there. This works because the electric field is defined as force per unit charge, so it lets us describe the influence of charges without depending on the particular test charge used.
When to use it
Use this formula when you know the electric force on a charge and want to find the field, or when you want to compare field strength at different points in space. It is common in electrostatics problems involving point charges, charged plates, and field mapping.
Worked example, step by step
A +2.0 C test charge experiences a force of 10 N at a certain point. Use E = F/q E = 10 N / 2.0 C E = 5 N/C Final answer: the electric field is 5 N/C at that point.
Common mistakes to avoid
- Using the charge of the source object instead of the test charge in the formula
- Forgetting that electric field is a vector and has direction as well as magnitude
- Mixing up units and writing the answer in newtons instead of newtons per coulomb
Did You Know?
Electric fields are invisible but real enough to make your hair stand on end near a Van de Graaff generator.
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