Author: haroonkhan

We will need a radiation counter to continue our exploration of the subatomic world, so let’s discuss gas-filled radiation detectors, especially the type commonly known as a Geiger counter. As shown in Figure 56, a gas-filled radiation detector is simply a metal cylinder filled with an inert gas. A thin center wire is kept at high…

Thomson concluded that the negatively charged particle of cathode rays must be a fundamental part of matter itself. His model presented the atom containing a large number of smaller bodies, which he still called corpuscles. Since common atoms are electrically neutral, Thomson proposed that the atom comprises separate negative and positive parts. The negative corpuscles (electrons)…

An even simpler, although less accurate, adaptation of Thomson’s setup to measure e/m can be built using a surplus “magic eye” tube. These electron vacuum tubes were commonly used in tube radios as a visual aid for tuning. The purpose of a magic eye tuning tube in these radio receivers was to help tune a station at…

It is possible to use a modern CRT to measure e/m using Thomson’s method. However, it isn’t an easy task, because the deflection plates are relatively small, and their position is not well known due to the graphite coating used to reduce charge accumulation beyond the neck of the CRT. For this reason, specialized CRTs are made…

In his third experiment, Thomson measured the mass-to-charge ratio (m/e) of the cathode rays. His setup allowed him to measure how much energy the rays carried and how much they were deflected by a magnetic field while also being deflected by an electric field. Figure 50 shows a simplified version of the apparatus. A potential difference V accelerates…

The tube that Thomson built for his electrostatic deflection experiment (Figure 46) is the grandfather of the modern oscilloscope CRT.** As shown in Figure 48, the basic structures of Thomson’s tube are still recognizable in the modern CRT. The main difference is in the replacement of the “cold cathode,” where cathode-ray production relies on stripping electrons by…

For his second crucial experiment, Thomson reattempted to deflect the cathode rays, much like Hertz had unsuccessfully tried before, but this time pulling a deeper vacuum in the tube. As shown in Figure 46, the cathode rays in his tube were made to pass between two parallel aluminum plates. Contrary to Hertz’s experience, the cathode rays…

Hertz’ (mistaken) finding that cathode rays were not deflected by an electric field was a true mystery, given that cathode rays were so easily bent by magnetic fields. In 1895, French physicist, and later Nobel Prize laureate, Jean Perrin built a CRT to investigate whether or not cathode rays transported charge.10 A diagram of Perrin’s original…

In 1879, Crookes had reached the conclusion that cathode rays must be particles of some sort, observing that they traveled in straight lines and were stopped by metallic objects in their path. As a demonstration, Crookes inserted an electrode shaped like a Maltese cross in the tube, and it cast a sharp shadow on the…

Some of the most important experiments to explain radiation were conducted in 1897 by British physicist J. J. Thomson. These experiments led Thomson to the discovery of the electron, for which he received the 1906 Nobel Prize in Physics. The story starts in 1857, when German physicist and glassblower Heinrich Geissler pumped the air out…