A point charge q = 10 μC is in air. Calculate field strength 0.5 m away.

Solution & explanation

1. Given: q = 10 μC; r = 0.5 m; k = 9×10⁹.

2. Convert microcoulombs.

   $$q=\frac{10}{1000000}=\frac{1}{{10}^5}$$

3. Use point-charge field.

   $$E=\frac{k\times q}{r^2}$$

4. Substitute.

   $$E=\frac{9000000000}{25000.0}$$

5. Square distance before division.

   $$E=\frac{90000}{0.25}=360000$$

6. State the result with units: E = 3.6×10⁵ N C⁻¹, radially outward.

E = 3.6×10⁵ N C⁻¹