Physics · UNITS AND MEASUREMENT

Plane angle \( d\theta \) and solid angle \( d\Omega \) are defined as the ratio of arc length to radius and intercepted area to square of radius, respectively. Which of the following statements is correct regarding their dimensions and units?

1. Both have neither units nor dimensions.
2. Both have SI units (radian and steradian) but are dimensionless.
3. Plane angle has dimension \( [L] \) and solid angle has dimension \( [L^2] \).
4. Plane angle is dimensionless but solid angle has dimension \( [L^2] \).