Question

What is the ratio of mass of proton and electron?
  (a)$1.836 \times {10^3} $
  (b)$1.836 $
  (c)$1.836 \times {10^2} $
  (d)$1.836 \times {10^{ - 3}} $

Answer 1

Hint: An electron is a fundamental particle that has a negative charge and the mass of the electron is $9.11 \times {10^{ - 28}}g$, and a proton is a fundamental particle that has a positive charge and the mass of a proton is $1.67 \times {10^{ - 24}}g$.

Complete answer:
As we know an atom is neutral, so the number of electrons will be equal to the number of protons. The negative charge is due to electrons and the positive charge is due to protons. The charge of a proton is $1.6 \times {10^{ - 19}}C$ and the mass of the proton is $1.67 \times {10^{ - 24}}g$.
Same as protons, the charge of electrons is $ - 1.6 \times {10^{ - 19}}C$ and the mass of electrons is $9.11 \times {10^{ - 28}}g$.
So, the ratio of the mass of the proton to the mass of electron is:
$\dfrac{mass\ of\ proton}{mass\ of\ electron}$
$\dfrac{{1.67 \times {{10}^{ - 24}}}}{{9.11 \times {{10}^{ - 27}}}}$$ = 1835$
Or it can be written as: $1.835 \times {10^3} \approx 1.836 \times {10^3}$
Discovery of proton: protons were discovered from anode rays. When high voltage is passed between the electrodes then it was found that some rays were coming from the side of the anode which passed through the holes in the cathode and produced green fluorescence. These rays were called anode rays or canal rays or positive rays.
Discovery of electrons: electrons were discovered from cathode rays. When high voltage is passed between the electrodes it was found that at very low pressure rays from the cathode were passed to the holes of the anode which had a faint greenish color. These are called cathode rays and carry a negative charge.

Note:
Both the rays i.e. anode rays and cathode rays travel in a straight line. The mass of both particles was calculated by dividing the charge to the ratio of charge to mass. The ratio of charge to mass of a proton is $9.58\times 10 ^{4}\;Cg^{-1}$ and that of the electron is $1.76\times 10 ^{8}\;Cg^{-1}$.