## The Bohr model for the spectra of a H-atom

Q: The Bohr model for the spectra of a H-atom

(a) will not be applicable to hydrogen in the molecular from

(b) will not be applicable as it is for a He-atom

(c) is valid only at room temperature

(d) predicts continuous as well as discrete spectral lines

Ans: (a) & (b)

## A set of atoms in an excited state decays

Q: A set of atoms in an excited state decays

(a) in general to any of the states with lower energy

(b) into a lower state only when excited by an external electric field

(c) all together simultaneously into a lower state

(d) to emit photons only when they collide

Ans: (a)

## For the ground state, the electron in the H-atom has an angular momentum = h, according to the simple Bohr model. Angular momentum is a vector and hence ….

Q: For the ground state, the electron in the H-atom has an angular momentum = h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,

(a) because Bohr model gives incorrect values of angular momentum

(b) because only one of these would have a minimum energy

(c) angular momentum must be in the direction of spin of electron

(d) because electrons go around only in horizontal orbits

Ans: (a)

## In a Rutherford scattering experiment when a projectile of z1 and mass M1 approaches a target nucleus of charge z2 and mass M2. The distance of closest approach is r_0. The energy of the projectile is

Q: In a Rutherford scattering experiment when a projectile of z1 and mass M1 approaches a target nucleus of charge z2 and mass M2. The distance of closest approach is r0 . The energy of the projectile is

(a) Directly proportional to M1 × M2

(b) Directly proportional to z1z2

(c) Inversely proportional to z1

(d) Directly proportional to mass M1

Ans: (b)

Sol: $\large \frac{1}{2}M_1 v^2 = \frac{1}{4\pi \epsilon_0} \frac{(Z_1 e)(Z_2 e)}{r_0}$

Where r0 = distance of closest approach

$\large r_0 = \frac{1}{4\pi \epsilon_0} \frac{(Z_1 e)(Z_2 e)}{\frac{1}{2}M_1 v^2}$

## A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by

Q: A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by

(a) 1.05 × 10-34 J-s

(b) 3.16 × 10-34 J-s

(c) 2.11 × 10-34 J-s

(d) 4.22 × 10-34 J-s

Ans: (a)