What did J.J. Thomson's experiments with cathode ray tubes imply about the mass of an electron?

• A. The mass of an electron is greater than the mass of a neutron.
• B. The mass of an electron is approximately 1 amu.
• C. The mass of an electron is equal to the mass of a proton.
• D. The mass of an electron is much smaller than that of a hydrogen atom.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the context of J.J. Thomson's cathode ray tube experiments, which involved studying the properties of cathode rays (streams of electrons) in a vacuum tube under the influence of electric and magnetic fields.
2. Step 2: Recognize that Thomson measured the charge-to-mass ratio (\(\frac{e}{m}\)) of the particles in the cathode rays, discovering that this ratio was much larger than that of any known ion, implying either a very large charge or a very small mass.
3. Step 3: Since the charge of the electron was later determined to be the same magnitude as the charge of a proton, Thomson concluded that the mass of the electron must be much smaller than that of atoms or protons.
4. Step 4: Connect this conclusion to the fact that the electron's mass is indeed much smaller than the mass of a hydrogen atom (which contains one proton and one electron), confirming that electrons are subatomic particles with very small mass.
5. Step 5: Summarize that Thomson's experiments implied the electron has a mass much smaller than that of atoms, disproving options that suggest the electron's mass is comparable to protons, neutrons, or 1 amu.