Question

The order(lowest to highest) of e/m(charge/mass) ratio of electron (e),proton(p),neutron(n) and alpha particle($\alpha$) is:
A. e ,p ,n, $\alpha$
B. n, p, e, $\alpha$
C. n, p, $\alpha$, e
D. n, $\alpha$, p, e

Answer 1

We can solve this question by dividing the charge of a species by its mass. Important application of charge by mass ratio is mass spectrometer. Also this principle is used to extract information in experiments involving the cloud chamber.

Complete step by step solution: Let us discuss electrons, protons, neutrons and alpha particles before going directly onto the question.
Electrons are discovered by English physicist JJ Thomson and it is a subatomic particle that possesses a charge of magnitude -1.Electron and proton have equal magnitude of charge which makes an atom neutral. (Mass of electron is roughly 1/1836 the mass of proton).Electron have negative charge $1.602 \times {10^{ - 19}}C$ and mass of electron is $9.1093 \times {10^{ - 31}} Kg$.
Proton was discovered by Goldstein in the year 1886.Mass of proton is equal to that of the hydrogen atom. Mass of the proton is 1840 times the mass of an electron. Mass of proton is $1.672 \times {10^{ - 27}}Kg$ and positive charge on proton is $1.602 \times {10^{ - 19}}C$.
Neutron was discovered by James chadwick. It has 0 charge that is why neutrons are neutrally charged subatomic particles. Mass of the neutron is $1.674 \times {10^{ - 27}}Kg$.
Alpha particle is a positively charged particle consisting of two protons and two neutrons bound together, thus having a mass of four times the mass of the proton and a positive charge two times the mass of the proton.
So we have discussed all species and now we can compare the charge by mass ratio.
On comparing we get e>p>$\alpha$>n.

So our correct option is option (D).

Note: The important thing to remember is that we can take mass of alpha particles in equivalence of the Helium atom.Remember all the properties of all the species thoroughly and also read about alpha, beta and gamma particles to solve similar types of questions.