The hydrogen atom is excited from ground state to another state with the principal quantum number equal to 4. Then the number of spectral lines in the emission spectra will be
2
3
3
3
D.
3
Number of spectral lines from a state n to ground state is
The radiation corresponding to 3 → 2 transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of 3 x 10^{-4} T. If the radius of the largest the circular path followed by these electrons is 10.0 mm, the work function of the metal is close to:
1.8 eV
1.1 eV
0.8 eV
0.8 eV
B.
1.1 eV
mv =qBR
The energy spectrum of β-particles [number N(E) as a function of β-energy E] emitted from a radioactive source is
C.
The potential energy function for the force between two atoms in a diatomic molecule is approximately given by where a and b are constants and x is the distance between the atoms. If the dissociation energy of the molecule is D = [U(x = ∞) – U_{at equilibrium}], D is
b^{2}/2a
b^{2}/12a
b^{2}/4a
b^{2}/4a
C.
b^{2}/4a
The potential energy for diatomic molecule is
The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy?
lll
IV
I
I
A.
lll
Energy required for the electron excitation in Li^{++} from the first to the third Bohr orbit is
36.3 eV
108.8 eV
122.4 eV
122.4 eV
B.
108.8 eV
Which of the following transitions in hydrogen atoms emit photons of highest frequency?
n = 2 to n = 6
n = 6 to n = 2
n = 2 to n =1
n = 2 to n =1
C.
n = 2 to n =1
In a hydrogen like atom, electron makes the transition from an energy level with quantum number n to another with a quantum number (n – 1). If n >> 1, the frequency of radiation emitted is proportional to
1/n
1/n^{2}
1/n^{3/2}
1/n^{3/2}
D.
1/n^{3/2}
An energy gap, ΔE = hv
Here, h is Planck's constant
therefore,
Frequency
If a source of power 4kW produces 10^{20} photons/second, the radiation belongs to a part of the spectrum called
X -rays
ultraviolet rays
microwaves
microwaves
A.
X -rays
As power of source = 4 x 10^{3} = 10^{20} x hv
(∴ P/E = Number of photons)
Suppose an electron is attracted towards the origin by a force k/r where ‘k’ is a constant and ‘r’ is the distance of the electron from the origin. By applying Bohr model to this system, the radius of the nth orbital of the electron is found to be ‘rn’ and the kinetic energy of the electron to be Tn. Then which of the following is true?
T_{n} ∝ 1/n^{2}, r_{n} ∝ n^{2}
T_{n} independent of n, r_{n} ∝ n
T_{n} ∝ 1/n, r_{n} ∝ n
T_{n} ∝ 1/n, r_{n} ∝ n
B.
T_{n} independent of n, r_{n} ∝ n