Physics Class 12 NCERT Solutions: Chapter 12 Atoms Part 1

Q: 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 less 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.)

(A) The sizes of the atoms taken in Thomson’s model and Rutherford’s model have the same order of magnitude.

(B) In the ground state of 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 Rutherford’s model is doomed to collapse.

(D) An atom has a nearly continuous mass distribution in 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 both the models.

Q: 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.) What results do you expect?

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 α-particles. Thus, the mass of the scattering particle is more than the target nucleus (hydrogen). As a result, the α-particles would not bounce back if solid hydrogen is used in the α-particle scattering experiment.

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

Rydberg’s formula is given as:

Where,

The shortest wavelength present in the Paschen series of the spectral lines is given for values.

Q: 4. A difference of separates two energy levels in an atom. What is the frequency of radiation emitted when the atom makes a transition from the upper level to the lower level?

Separation of two energy levels in an atom,

Let be the frequency of radiation emitted when the atom transits from the upper level to the lower level.

We have the relation for energy as:

Where,

Hence, the frequency of the radiation is.

Q: 5. The ground state energy of hydrogen atom is. What are the kinetic and potential energies of the electron in this state?

Ground state energy of hydrogen atom,

This is the total energy of a hydrogen atom. Kinetic energy is equal to the negative of the total energy.

Kinetic energy = – E = – (- 13.6) = 13.6 eV

Potential energy is equal to the negative of two times of kinetic energy.

Potential energy