The question asks to identify the scientist who discovered the electron. This is a fundamental concept in atomic structure and requires knowledge of key historical scientific discoveries.
B) J.J. Thomson — J.J. Thomson is credited with the discovery of the electron in 1897 through his work on cathode rays. He proved that these rays were streams of negatively charged particles, much smaller than atoms.
The question asks for the approximate charge-to-mass ratio (e/m) of an electron. This is a fundamental constant in physics that candidates are expected to know or be able to derive from the known values of the elementary charge and electron mass.
The charge-to-mass ratio (\(e/m\)) is calculated as:
\[ \frac{e}{m} = \frac{1.602 \times 10^{-19} \text{ C}}{9.109 \times 10^{-31} \text{ kg}} \]
Performing the division:
\[ \frac{e}{m} \approx 0.1758 \times 10^{(-19 - (-31))} \text{ C/kg} \]
\[ \frac{e}{m} \approx 0.1758 \times 10^{12} \text{ C/kg} \]
To express this in standard scientific notation:
\[ \frac{e}{m} \approx 1.758 \times 10^{11} \text{ C/kg} \]
This value matches option C.
Correct Option: C) 1.758 \times 10^11 C/kg
The question asks to identify the scientist who determined the charge of an electron using the oil drop experiment. This requires knowledge of fundamental experiments in atomic physics and the scientists associated with them.
A) R.A. Millikan — Robert Andrews Millikan, in collaboration with Harvey Fletcher, performed the oil drop experiment in 1909. This experiment allowed them to measure the elementary electric charge, which is the charge of a single electron. By observing the motion of tiny charged oil droplets suspended between two metal electrodes, they could determine the charge on each droplet and found it to be an integral multiple of a fundamental charge, thus determining the charge of an electron.
The question asks for the approximate mass of an electron. This is a fundamental constant in physics and chemistry that candidates preparing for competitive exams are expected to know. We need to identify the correct value from the given options.
Correct Option: C) The mass of an electron is approximately \(9.109 \times 10^{-31}\) kg. This is the internationally accepted value for the rest mass of an electron.
The question asks about the discovery of the proton. We need to identify the scientist(s) credited with this discovery from the given options.
D) Ernest Rutherford / E. Goldstein — E. Goldstein first observed positive rays (canal rays) in 1886, which were later identified by Ernest Rutherford as protons in 1920. Rutherford also named the particle. Therefore, both scientists are credited with the discovery.
The question asks to identify the scientist credited with the discovery of the neutron. This requires knowledge of the history of atomic structure and the key contributions of prominent physicists.
A) James Chadwick discovered the neutron in 1932. His experiments involved bombarding beryllium with alpha particles, leading to the emission of highly penetrating neutral radiation, which he identified as neutrons.