Modern Physics Class 12 MCQ. We covered all the Modern Physics Class 12 MCQ in this post for free so that you can practice well for the exam.
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MCQ on Modern Physics for Class 12 Students
Line spectrum is obtained whenever the incandescent vapors at low pressure of the excited substance are in their
(a) atomic state
(b) molecular state
(c) nuclear state
(d) None of these
Option a – atomic state
Which of the following statements are true regarding Bohr’s model of the hydrogen atom? (I) Orbiting speed of the electron decreases as it shifts to discrete orbits away from the nucleus (II) Radii of allowed orbits of the electron are proportional to the principal quantum number (III) Frequency with which electrons orbit around the nucleus in discrete orbits is inversely proportional to the cube of principal quantum number (IV) Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits Select the correct answer using the codes given below. Codes :
(a) I and II
(b) II and IV
(c) I, II, and III
(d) II, III, and IV
Option a – I and II
Which of the following series in the spectrum of hydrogen atoms lies in the visible region of the electromagnetic spectrum?
(a) Paschen series
(b) Balmer series
(c) Lyman series
(d) Brackett series
Option b – Balmer series
Electron emission from a metallic surface by the application of light is known as
(a) Thermionic emission
(b) Photoelectric emission
(c) High-field emission
(d) Auto electronic emission
Option b – Photoelectric emission
If the potential difference applied to an X-ray tube is doubled while keeping the separation between the filament and the target as same, what will happen to the cutoff wavelength?
(a) Will remain the same
(b) Will be doubled
(c) Will be halved
(d) Will be four times the original wavelength
Option c – Will be halved
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
Option b – increases
The wavelength of characteristic X-rays depends upon
(a) the temperature of the target
(b) the size of the target
(c) the atomic number of the target
(d) the mass of the target
Option c – the atomic number of the target
White X-rays are called white due to the fact that
(a) they are electromagnetic radiations having nature the same as that of white light.
(b) they are produced most abundantly in X-ray tubes.
(c) they have a continuous wavelength range.
(d) they can be converted to visible light using coated screens and photographic plates are affected by them just like light.
Option c – they have a continuous wavelength range
When a hydrogen atom is raised from the ground state to an excited state
(a) P.E. increases and K.E. decreases
(b) P.E. decreases and K.E. increases
(c) Both energy (K.E. and P.E.) increases
(d) Both K.E. and P.E. decreases
Option a – P.E. increases and K.E. decreases
As the quantum number increases, the difference in energy between consecutive energy levels
(a) remains the same
(b) increases
(c) decreases
(d) sometimes increases and sometimes decreases.
Option c – decreases
The photoelectric effect can be understood on the basis of
(b) electromagnetic theory of light only
(c) quantum theory of light only
(d) None of these
Option c – quantum theory of light only
When light is incident on a metal surface the maximum kinetic energy of emitted electrons
(a) vary with the intensity of light
(b) varies with the frequency of light
(c) varies with the speed of light
(d) varies irregularly
Option b – varies with the frequency of light
A photo-sensitive metal is not emitting photo-electrons when irradiated. It will do so when the threshold is crossed. To cross the threshold we need to increase
(a) intensity
(b) frequency
(c) wavelength
(d) None of these
Option b – frequency
The work function for the photoelectric effect
(a) is different for different metals
(b) is the same for all metals
(c) depends upon the intensity of incident light
(d) depends upon the frequency of incident light
Option a – is different for different metals
In the photoelectric effect, electrons are emitted
(a) at a rate that is proportional to the amplitude of the incident radiation
(b) with a maximum velocity proportional to the frequency of the incident radiation
(c) at a rate that is independent of the emitter
(d) only if the frequency of the incident radiations is above a certain threshold value
Option d – only if the frequency of the incident radiations is above a certain threshold value
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