3
MCQ (Single Correct Answer)
The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because
A
of the electrons not being subject to a central force
B
of the electrons colliding with each other
C
of screening effects
D
the force between the nucleus and an electron will no longer be given by Coulomb's law
4
MCQ (Single Correct Answer)
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
5
MCQ (Single Correct Answer)
$\mathrm{O}_2$ molecule consists of two oxygen atoms. In the molecule, nuclear force between the nuclei of the two atoms
A
is not important because nuclear forces are short-ranged
B
is as important as electrostatic force for binding the two atoms
C
cancels the repulsive electrostatic force between the nuclei
D
is not important because oxygen nucleus have equal number of neutrons and protons
6
MCQ (Single Correct Answer)
Two H atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced is
A
10.20 eV
B
20.40 eV
C
13.6 eV
D
27.2 eV
7
MCQ (Single Correct Answer)
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