Absorption of an individual electrons captured on film

University of Gothenburg

Researchers at the University of Gothenburg have observed the absorption of a single electron by a levitated droplet with such a magnification that it is visible with the naked eye and can even be measured with a normal millimeter scaled ruler.

Matter in the universe is composed of elementary particles like electrons, protons, and neutrons. They are everywhere, but they are so small that the human eye cannot discern them. In the last century, physicists have proven the existence of these particles through different experiments, but in most cases the observation of the particles have been indirect.

Image
Javier Tello Marmolejo.

Javier Tello Marmolejo.
Photo: GU

– Electrons are one of these fundamental particles. In 1909, Robert Millikan proved that the charge of the electron is quantized. In other words, there exists a minimum, indivisible amount of charge. He demonstrated that the electron´s charge is quantized by letting hundreds of charged droplets fall in an electric field and then perform a statistical analysis of their motion.

An experiment with a single levitated drop

-Now we have created a modern version of this classical experiment by levitating a single droplet in air using a laser, says Javier Marmolejo, Ph.D. at the Department of physics at the University of Gothenburg.

In this experiment, the quantization of the electric charge is directly visible for the first time without advanced equipment or a complex statistical analysis.

– We trapped a drop using a laser inside a strong electric field and added individual electrons by exposing it to alfa radiation. The drop performed quantized jumps every time it absorbed one or a few electrons. By magnifying the image of the droplet using a single lens, we were able to see the effect of a single electron absorption and to measure the jumps with a ruler. The bright spot moved about one millimeter for every absorbed electron (see video).

The drop had a diameter of 29 micrometers, which roughly corresponds to the thickness of a thin human hair. Despite this, it contains around 3.7 x1015 negatively charged electrons.

– The feat is incredible when one considers that the effect of adding single electron to a droplet that already has 3 700 000 000 000 000 is visible with the naked eye.

Now that it is possible to “see the effect of a single electron”, a new opportunity emerges to better communicate science regarding elementary particles to the general public, the researchers comment.

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