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
two
three
four
four
B.
three
Ionization energy corresponding to ionization potential = -13.6 eV.
Photon energy incident = 12.1 eV
So, the energy of electron in excited state
= -13.6 + 12.1 = -1.5 eV
i.e.,
i.e., energy of electron in excited state corresponds to third orbit.
The possible spectral lines are when electron jumps from orbit 3rd to 2nd; 3rd to 1st and 2nd to 1st. Thus, 3 spectral lines are emitted.
A microscope is focussed on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?
1 cm upward
4.5 cm downward
1 cm downward
1 cm downward
A transistor is operated in common emitter configuration at constant collector voltage Vc = 1.5 V such that a change in the base current from 100 µA to 150 µA produces a change in the collector current from 5 mA to 10 mA. The current gain (β) is
67
75
100
100
A photo-cell employs photoelectric effect to convert
change in the frequency of light into a change in electric voltage
change in the intensity of illumination into a change in photoelectric current
change in the intensity of illumination into a change in the work function of the photocathode
change in the intensity of illumination into a change in the work function of the photocathode
When photons of energy hv fall on an aluminium plate (of work function E0), photoelectrons of maximum kinetic energy K are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be
K+E0
2K
K
K
The following figure shows a logic gate circuit with two inputs A and B and the output C. The voltage waveforms of A, B and C are as shown below:
The logic curcuit gate is
AND gate
NAND gate
NOR gate
NOR gate
The radius of germanium (Ge) nuclide is measured to be twice the radius of The number of nucleons in Ge are
73
74
75
75
A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is
25
50
infinite
infinite