PhysRefPhysics reference
Electricity & Magnetism
E=Fq=kQr2E = \frac{F}{q} = k\frac{Q}{r^2}

Electric field is force per unit charge.

Variables

E
Electric field
Field strength
In SI units: kg·m/(A·s³)
N/C
F
Force
Force on test charge
In SI units: kg·m/s²
N
q
Test charge
Small positive charge
In SI units: A·s
C
Q
Source charge
Field-creating charge
In SI units: A·s
C
r
Distance
From source
Allowed values: greater than 0
m

Derivation

E = F/q by definition. For point charge: E = kQ/r².

Your notes

0/5000

Check value

Round inputs run through this page's calculator. Use it to test your own working or a rearranged form. It is a test case, not a real-world example.

  • F = 2 N (Force)
  • q = 3 C (Test charge)

Result: E = 0.66666667 N/C

Other electricity & magnetism formulas with the same quantities

Where this formula is listed

Common questions

What is the Electric Field formula?

Electric Field is written E = F/q = k(Q/r²). Electric field is force per unit charge. It belongs to Electricity & Magnetism, under Electrostatics.

What are the units in E = F/q = k(Q/r²)?

In SI units, E is electric field, measured in kg·m/(A·s³); F is force, measured in kg·m/s²; q is test charge, measured in A·s; Q is source charge, measured in A·s; r is distance, measured in m.

How is the Electric Field formula derived?

E = F/q by definition. For point charge: E = kQ/r². The result is E = F/q = k(Q/r²).