# Atoms

## Physics

### NCERT

1   Choose the correct alternative from the clues given at the end of the each statement:$\\$ (a) The size of the atom in Thomson's model is -------- the atomic size in Rutherford's model. (much greater than/no different from/much than.)$\\$ (b) In the ground state of ------------ electrons are in stable equilibrium, while in ....... electrons always experience a net force. (Thomson's model/ Rutherford's model.)$\\$ (c) A classical atom based on ---------- is doomed to collapse. (Thomson's model/ Rutherford's model.)$\\$ (d) An atom has a nearly continuous mass distribution in a--------- but has a highly non- uniform mass distribution in _____ (Thomson's model/ Rutherford's model.)$\\$ (e) The positively charged part of the atom possesses most of the mass in --------- (Rutherford's model/both the models.)

##### Solution :

(a) The sizes of the atoms taken in Thomson's model and Rutherford's model have the $\underline{same \ order \ of \ magnitude.}$$\\ (b) In the ground state of \underline{Thomson's \ model}, the electrons are in stable equilibrium. However, in Rutherford's model, the electrons always experience a net force.\\ (c) A classical atom based on \underline{Rutherford's \ model} is doomed to collapse.\\ (d) An atom has a nearly continuous mass distribution in \underline{Thomson's \ model}, but has a highly non-uniform mass distribution in {Rutherford's \ model.}$$\\$ (e) The positively charged part of the atom possesses most of the mass in $\underline{both the models.}$

2   Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below $14 K.$) What results do you expect?

##### Solution :

In the alpha-particle scattering experiment, if a thin sheet of solid hydrogen is used in place of a gold foil, then the scattering angle would not be large enough. This is because the mass of hydrogen is less than the mass of incident $\alpha$ - particles Thus, the mass of the scattering particle is more than the target nucleus (hydrogen). As a result, the $\alpha$- particles would not bounce back if solid hydrogen is used in the $\alpha -$ particle scattering experiment and so we cannot determine size of the hydrogen

3   What is the shortest wavelength present in the Paschen series of spectral lines?