circularly polarized light
Summary
Circularly polarized light is a transverse wave whose electric field keeps constant magnitude and rotates around the direction of travel, made of two perpendicular components of equal amplitude 90° out of phase. Plane-polarized light is the sum of left and right circular light, which underlies optical activity.
Detail
Meaning: Circularly polarized light is a transverse electromagnetic wave whose electric field vector has constant magnitude but rotates about the direction of travel, tracing a helix in space and a circle when viewed head-on. It is the sum of two perpendicular linear components of equal amplitude that are 90° out of phase. The rotation sense gives right-handed or left-handed light. Unequal amplitudes or another phase difference give elliptical light.
On the MCAT: Most polarization items use linear light, polarizers, and Malus's law. Circular light appears conceptually: a quarter-wave plate can convert linear light to circular, and in organic chemistry plane-polarized light is treated as equal parts left and right circular light. A chiral sample interacts with the two differently, which rotates the plane of polarization (optical activity).
Common confusion: Students picture the wave moving around a circle or being longitudinal. It remains transverse and travels straight ahead; what rotates is the field direction. Also, circular light is not the same as unpolarized light: its field direction is perfectly defined at every instant, although an ideal linear polarizer passes half its intensity at any orientation.
Sources
- Physics (Giancoli)
- Fundamentals of Physics (Halliday, Resnick, Walker)
- University Physics (Young and Freedman)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.