NCERT Class 12 Physics Chapter 12 Atoms MCQs & PYQ

1.

In the α particle scattering experiment, the shape of the trajectory of the scattered α particles depend upon :

(a) only on impact parameter.

(b) only on the source of α particles.

(c) both impact parameter and source of α particles.

(d) impact parameter and the screen material of the detector.

2.

The radius of the nth orbit in Bohr model of hydrogen atom is proportional to :

(a)       (b)        (c) n2       (d) n

3.

Hydrogen atom initially in the ground state, absorbs a photon which excites it to n = 5 level. The wavelength of the photon is:

(a) 975 nm       (b) 740 nm       (c) 523 nm       (d) 95 nm

4.

A hydrogen atom makes a transition from 𝑛 = 5 to 𝑛 = 1 orbit. The wavelength of the photon emitted is 𝜆. The wavelength of photon emitted when it makes a transition from 𝑛 = 5 to 𝑛 = 2 orbit is

(a)      (b)      (c)      (d)

5.

The potential energy of an electron in the second excited state in hydrogen atom is :

(a) –3·4 eV       (b) –3·02 eV       (c) –1·51 eV       (d) –6·8 eV

1. Draw the graph showing the variation of the number (N) of scattered alpha particles with scattering angle (θ) in Geiger - Marsden experiment. Infer two conclusions from the graph.

2. (i) Define the terms : ‘impact parameter’ and ‘distance of closest approach’ for an α-particle in Geiger-Marsden scattering experiment.

3. What results do you expect if α-particle scattering experiment is repeated using a thin sheet of hydrogen in place of a gold foil? Explain. (Hydrogen is a solid at temperature below 14K)

4. (a) In Geiger-Marsden experiment, the distance of closest approach is considerably larger than the sum of the radii of the gold nucleus and the α-particle. Explain.

5. In Geiger-Marsden scattering experiment, the trajectory of α-particles in Coulomb’s field of a heavy nucleus is shown in the figure.