The question asks for the earliest and simplest observation that inferred the existence of charged particles within matter. We need to evaluate each option based on its historical context and the fundamental nature of the phenomenon described.
D) When two objects are rubbed together, they acquire electric charges — indicating that atoms contain charged particles
This observation of static electricity (triboelectric effect) is one of the oldest and most direct pieces of evidence suggesting that matter is not simply neutral but contains mobile charged constituents. The transfer of these charges during rubbing leads to the objects becoming charged, thus inferring the presence of charged particles within their atomic structure.
The question asks to identify the scientist who discovered electrons and the year of their discovery. This requires knowledge of fundamental atomic structure history.
Correct Option: C) J.J. Thomson, 1897 (using cathode ray tube experiments)
The question asks to identify the correct description of cathode rays and the properties observed by J.J. Thomson. This requires knowledge of the historical experiments related to the discovery of the electron and its characteristics.
B) Cathode rays are streams of negatively charged particles (electrons) emitted from the cathode; they travel in straight lines, deflect towards positive plate in electric field, cause fluorescence, and have the same charge-to-mass ratio regardless of cathode material
This option accurately describes cathode rays as negatively charged particles (electrons) originating from the cathode. It correctly lists their properties: traveling in straight lines, deflection towards a positive plate in an electric field (indicating negative charge), causing fluorescence, and having a constant charge-to-mass ratio independent of the cathode material. These were all key observations made by J.J. Thomson.
A) Cathode rays are streams of protons emitted from the nucleus of the cathode material
This is incorrect. Cathode rays are electrons, which are negatively charged. Protons are positively charged and are much heavier than electrons. Also, electrons are emitted from the surface of the cathode, not necessarily from the nucleus.
C) Cathode rays are neutral electromagnetic waves similar to X-rays
This is incorrect. Cathode rays are streams of charged particles (electrons), not neutral electromagnetic waves. Electromagnetic waves (like X-rays) are not deflected by electric or magnetic fields, whereas cathode rays are.
D) Cathode rays are streams of positively charged particles from the anode
This is incorrect. Cathode rays originate from the cathode (negative electrode) and are negatively charged. Positively charged particles observed in discharge tubes are called anode rays or canal rays, which travel in the opposite direction (from anode towards cathode or from the gas towards cathode) and are not what J.J. Thomson primarily studied as "cathode rays".
The question asks about the type and magnitude of the charge carried by an electron. This is a fundamental concept in physics and chemistry, specifically related to atomic structure and electricity. We need to recall the established properties of an electron.
Correct Option: B) Negative charge; \(1.6 \times 10^{-19}\) coulombs (often called unit negative charge or –1)
This option correctly identifies both the type of charge (negative) and its magnitude (\(1.6 \times 10^{-19}\) coulombs), which is the standard value for the elementary charge.
The question asks about the discovery of protons, including the discoverer, year, and experimental setup. We need to evaluate each option based on historical facts regarding atomic structure discoveries.
D) E. Goldstein, 1886, using perforated cathode discharge tubes that showed 'canal rays' (anode rays) — streams of positively charged particles. Goldstein's experiments in 1886 with perforated cathodes in discharge tubes led to the observation of 'canal rays' or 'anode rays', which were streams of positively charged particles. This was the first experimental evidence of positive particles within atoms, paving the way for the later understanding and naming of the proton.
This question asks about the relative mass of an electron compared to a proton. This is a fundamental concept in atomic structure and requires knowledge of the approximate masses of these subatomic particles.
\[ \frac{m_e}{m_p} = \frac{9.109 \times 10^{-31} \text{ kg}}{1.672 \times 10^{-27} \text{ kg}} \]
\[ \frac{m_e}{m_p} \approx 0.000544 \approx \frac{1}{1838} \]
More precisely, the ratio is about \(1/1836\).
This means that the mass of an electron is approximately \(1/1836\) times the mass of a proton, which is often rounded to \(1/2000\) for simplicity in many contexts.