Portable Optical Tweezers Kit
Chapter 6: Experiments
Page 68
MTN024417-D02
Once the laser is switched off, the fat particle
moves back to the surface of the water.
6.5. The Holding Force of the Optical Trap
6.5.1. Brownian Motion
The proper motion or vibrating motion of particles, also referred to as Brownian motion,
can be observed under the optical tweezers. Samples can be found at
Exercise
Explain briefly the causes of Brownian motion and what role it plays in the experiments
with the optical tweezers.
Solution
Brownian motion is the statistic vibrating motion (translation and rotation) of microscopic
free particles. Under the microscope, the paths of particles are seen as short, straight lines
(see Figure 52). The Brownian motion can be observed in experiments under the optical
tweezers. The polystyrene beads are located in a medium that consist of molecules. These
molecules are constantly moving in all directions. Because of this, the molecules
repeatedly bump into the beads, which causes a vibrating motion of the beads that can be
observed under the optical tweezers. The molecules move more the higher the
temperature.
Summary of Contents for EDU-OT3
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