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NCERT Solutions for class 12 Physics | Chapter 12 - Atoms

(1) The binding energy of a deuteron is about:
[A] 2.22 MeV
[B] 2.22 J
[C] 2.22 eV
[D] None of these
Answer: 2.22 MeV
(2) Artificial radioactivity was discovered by:
[A] Joliot
[B] Becquerel
[C] Pauli
[D] None of these
Answer: Joliot

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(3) The principle that a quantum orbital cannot be occupied by more than two electrons was given by:
[A] Pauli
[B] Millikan
[C] Hund
[D] None of these
Answer: Pauli
(4) Isotones have the same:
[A] A
[B] Z
[C] N
[D] All the above
Answer: N
(5) Fg and Fe represents the gravitational and electrostatic force respectively between two electrons situated at some distance the ratio  is if the order of:
[A] 9.8
[B] 109
[C] 1042
[D] 10-42
Answer: 10-42
(6) Isobars have the same:
[A] A
[B] Z
[C] N
[D] All the above
Answer: A
(7) Who explained the splitting of special lines in magnetic field?
[A] Zeeman
[B] Bohr
[C] Summerfield
[D] Einstein
Answer: Zeeman
(8) An atom stays in an excited state for about:
[A] 10 micro seconds
[B] 10 milli seconds
[C] 10 nano seconds
[D] 10 seconds
Answer: 10 nano seconds
(9) In terms of Bohr radius r0, the radius of the second Bohr orbit of a hydrogen atom is given by
[A] 4 r0
[B] 8 r0
[C] √2 r0
[D] 2 r0
Answer: 4 r0
(10) When an atomic gas or vapour is excited at low pressure, by passing an electric current through it then
[A] emission spectrum is observed
[B] absorption spectrucm is observed
[C] band spectrum is observed
[D] both (b) and (c)
Answer: emission spectrum is observed
(11) When hydrogen atom is in its first excited level, it’s radius is
[A] four times, it ground state radius
[B] twice times, it ground state radius
[C] same times, it ground state radius
[D] half times, it ground state radius.
Answer: four times, it ground state radius
(12) Which of the following in a hydrogen atom is independent of the principal quantum number n? (The symbols have their usual meanings).
[A] νn
[B] Er
[C] En
[D] νr
Answer: Er
(13) Which of the following parameters is the same for all hydrogen-like atoms and ions in their ground states?
[A] Radius of the orbit
[B] Speed of the electron
[C] Energy of the atom
[D] Orbital angular momentum of the electron
Answer: Orbital angular momentum of the electron
(14) The electrons of Rutherford’s model would be expected to lose energy because, they
[A] move randomly
[B] jump on nucleus
[C] radiate electromagnetic waves
[D] escape from the atom
Answer: radiate electromagnetic waves
(15) According to classical theory, Rutherford’s atomic model is
[A] stable
[B] unstable
[C] meta stable
[D] both (a) and (b)
Answer: both (a) and (b)
(16) As one considers orbits with higher values of n in a hydrogen atom, the electric potential energy of the atom
[A] decreases
[B] increases
[C] remains the same
[D] does not increase
Answer: increases
(17) Rutherford’s atomic model was unstable because
[A] nuclei will break down
[B] electrons do not remain in orbit
[C] orbiting electrons radiate energy
[D] electrons are repelled by the nucleus
Answer: electrons do not remain in orbit
(18) Electrons in the atom are held to the nucleus by
[A] coulomb’s force
[B] nuclear force
[C] vander waal’s force
[D] gravitational force
Answer: coulomb’s force
(19) The angular speed of the electron in the nth orbit of Bohr hydrogen atom is
[A] directly proportional to n
[B] inversely proportional to n
[C] inversely proportional to n2
[D] inversely proportional to n3
Answer: inversely proportional to n3
(20) The significant result deduced from the Rutherford’s scattering experiment is that
[A] whole of the positive charge is concentrated at the centre of atom
[B] there are neutrons inside the nucleus
[C] α-particles are helium nuclei
[D] electrons are embedded in the atom
Answer: whole of the positive charge is concentrated at the centre of atom

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