Question

Which of the following scientist observed that cathode rays consist of negatively charged particles?

• A. John Dalton
• B. J.J.Thomson
• C. E. Goldstein
• D. James Chadwick

Answer 1

The correct option is B

J.J.Thomson

The explanation for the correct answer

Option B

• In 1897, J.J Thomson conducted an experiment to understand the existence and nature of electrons in an atom.
• He passed electricity at high voltage through a discharge tube containing gas at very low pressure.
• This leads to the ejection of a stream of particles from the negative electrode (Cathode).
• These streams of particles were named cathode rays since they were emitted by the cathode.
• When the cathode rays are subjected to an electric field, they get deflected towards the positively charged plate(anode) indicating that cathode rays are negatively charged.

The explanation for the incorrect answers

Option A

• In 1808 John Dalton propose an atomic theory.
• He has proposed that all matters, whether they are an element, compound, or mixture are composed of small indivisible particles known as atoms.
• He also stated that toms can be neither created nor destroyed.

Option C

• E.Goldstein discovered the positively charged particle by using a discharge tube filled with $\mathrm{Hydrogen}\left(\mathrm{H}\right)$.
• These positively charged particles have a charge equal to and opposite to that of electrons. Hence they are called protons.

Option D

• The scientist James Chadwick bombarded alpha radiation from a polonium source into a sheet of Beryllium ($\mathrm{Be}$).
• This resulting penetration does not carry any charge but their mass is equal to that of protons.
• They are named neutrons.

Thus, option B i.e., J.J.Thomson is the correct option.