What is the significance of thomson cathode ray experiment

As Thomson saw it, the negative charge and the cathode rays must somehow be stuck together: you cannot separate the charge from the rays. Thomson's apparatus in the second experiment. Now Thomson thought of a new approach. A charged particle will normally curve as it moves through an electric field, but not if it is surrounded by a conductor a sheath of copper, for example.

Thomson suspected that the traces of gas remaining in the tube were being turned into an electrical conductor by the cathode rays themselves. To test this idea, he took great pains to extract nearly all of the gas from a tube, and found that now the cathode rays did bend in an electric field after all.

In response, J. Thomson constructed some elegant experiments to find a definitive and comprehensive answer about the nature of cathode rays. His first experiment was to build a cathode ray tube with a metal cylinder on the end. This cylinder had two slits in it, leading to electrometers, which could measure small electric charges.

He found that by applying a magnetic field across the tube, there was no activity recorded by the electrometers and so the charge had been bent away by the magnet. This proved that the negative charge and the ray were inseparable and intertwined.

Like all great scientists, he did not stop there, and developed the second stage of the experiment, to prove that the rays carried a negative charge. To prove this hypothesis, he attempted to deflect them with an electric field.

Earlier experiments had failed to back this up, but Thomson thought that the vacuum in the tube was not good enough, and found ways to improve greatly the quality. For this, he constructed a slightly different cathode ray tube, with a fluorescent coating at one end and a near perfect vacuum.

Halfway down the tube were two electric plates, producing a positive anode and a negative cathode, which he hoped would deflect the rays. As he expected, the rays were deflected by the electric charge, proving beyond doubt that the rays were made up of charged particles carrying a negative charge.

This result was a major discovery in itself, but Thomson resolved to understand more about the nature of these particles. The third experiment was a brilliant piece of scientific deduction and shows how a series of experiments can gradually uncover truths.

Many great scientific discoveries involve performing a series of interconnected experiments, gradually accumulating data and proving a hypothesis. He decided to try to work out the nature of the particles. Rutherford with the assistance of Ernest Marsden and Hans Geiger performed a series of experiments using alpha particles.

Rutherford aimed alpha particles at solid substances such as gold foil and recorded the location of the alpha particle "strikes" on a fluorescent screen as they passed through the foil. Rutherford concluded that the atom consisted of a small, dense, positively charged nucleus in the center of the atom with negatively charged electrons surrounding it. Cathode rays from C pass through a slit in the anode A, and through another slit at B. They then passed between plates D and E and produced a narrow well-defined phosphorescent patch at the end of the tube, which also had a scale attached to measure any deflection.

When Hertz had performed the experiment he had found no deflection when a potential difference was applied across D and E. He concluded that the electrostatic properties of the cathode ray are either nil or very feeble. Thomson admitted that when he first performed the experiment he also saw no effect. Thomson did perform the experiment at lower pressure [higher exhaustion] and observed the deflection. Having established that cathode rays were negatively charged material particles, Thomson went on to discuss what the particles were.

To investigate this question Thomson made measurements on the charge to mass ratio of cathode rays. It also included a magnetic field that could be created perpendicular to both the electric field and the trajectory of the cathode rays. The deflection d at the end of the region is given by. This value was independent of both the gas in the tube and of the metal used in the cathode, suggesting that the particles were constituents of the atoms of all substances.

The range, which is related to the mean free path for collisions, and which depends on the size of the object, was 0. If the cathode ray traveled so much farther than a molecule before colliding with an air molecule, Thomson argued that it must be much smaller than a molecule. Thomson had shown that cathode rays behave as one would expect negatively charged material particles to behave.

They deposited negative charge on an electrometer, and were deflected by both electric and magnetic fields in the appropriate direction for a negative charge.