Modern Physics - Online Test (11-12-2016) - Class 12 MCQ

Imagine an atom made up of a proton and a hypothetical particle of double the mass of the electron but having the same charge as the electron. Apply the Bohr atom model and consider all possible transitions of this hypothetical particle to the first excited level. The longest wavelength photon that will be emitted has wavelength λ (given in terms of the Rydberg constant R for this hydrogen atom) equal to

The time taken by a photoelectron to come out after the photon strikes is approximately

The electron in a hydrogen atom makes a transition from n = n₁ to n₁ = n₂ state. The time period of the electron in the initial state (n₁) is eight times that in the final state (n₂). The possible values of n₁ and n₂ are

If λ₁ and λ₂ are the wavelengths of the first members of the Lyman and Paschen series respectively, then λ₁ : λ₂ is

The specific charge of a proton is 9.6 × 10⁷ C kg^–1. The specific charge of an alpha particle will be

When light of wavelength 300 nm (nanometer) falls on a photoelectric emitter, photoelectrons are liberated. For example emitter, however, light of 600 nm wavelength is sufficient for creating photomission. What is the ratio of the work functions of the two emitters?

The K_a X-ray emission line of tungsten occurs at λ = 0.021 nm. The energy difference between K and L levels in this atom is about

In terms of Ryderg constant R, the wave number of the first Balmer line is

A 5 watt source emits monochromatic light of wavelength 5000 Å. When placed 0.5 m away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m, the number of photoelectrons liberated will be reduced by a factor of

Ionization potential of hydrogen atom is 13.6 eV.  Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV.  According to Bohr’s theory, the spectral lines emitted by hydrogen will be

The minimum wavelength of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to

A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is

The de-Broglie wavelength of a tennis ball of mass 60 g moving with a velocity of 10 ms^–1 is approximately : (Planck’s constant, h = 6.63 × 10^–34 Js)

Hard X-rays for the study of fractures in bones should have a minimum wavelength of 10^–11 m. The accelerating voltage for electrons in X-ray machine should be

Energy levels A, B & and C of a certain atom corresponding to increasing values of energy i.e., E_A < E_B < E_C.  If λ₁, λ₂ and λ₃ are wavelengths of radiations corresponding to transitions C to B, B to A and C to A respectively, which of the following relations is correct?

Two identical photo cathodes receive light of frequencies f₁ and f₂. If the velocity of the photoelectrons (of mass m) coming out are respectively v₁ and v₂, then

A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move

A photocell is illuminated by a small bright source placed 1m away. When the same source of light is placed 0.5 m away, the number of electrons emitted by photo cathode would

According to Einstein’s photoelectric equation, the plot of the kinetic energy of the emitted photo-electrons from a metal versus the frequency of the incident radiation gives a straight line, whose slope

Bohr’s atom model assumes

As per Bohr model, the minimum energy (in eV) required to remove an electron from the ground state of doubly ionized Li atom (Z = 3) is

When high energetic cathode rays strike a heavy target of high melting point, then rays produced are

X-rays are produced when an element of high atomic weight is bombarded by high energy

According to Bohr theory, relation between main quantum number n and radius of orbit r is

In Bohr’s model, the atomic radius of the first orbit is r₀. Then, the radius of the third orbit is

Sodium and copper have work function 2.3 eV and 4.5 eV respectively. Then, the ratio of their threshold wavelength is nearest to

If the kinetic energy of a free electron doubles, its de-Broglie wavelength changes by the factor