# MCQ : Modern Physics (1 to 10)

1. The total energy of the electron in the hydrogen atom in the ground state is -13.6 eV. Which of the following is its kinetic energy in the first excited state?
(A) 13.6 eV
(B) 6.8 eV
(C) 3.4 eV
(D) 1.825 eV

2.A freshly prepared radioactive source of half life 2 hrs emits radiation of intensity which is 32 times the permissible safe value of intensity. Which of the following is the minimum time after which it would be possible to work safely with this source?
(A) 16 hrs
(B) 5 hrs
(C) 10 hrs
(D) 32 hrs

3.The ionisation potential of a hydrogen atom is 13.6 volt. The energy required to remove an electron from the second orbit of hydrogen is:
(A) 3.4 eV
(B) 6.8 eV
(C) 13.6 eV
(D) 27.2 eV

4.The radius of the first Bohr orbit is ao. The nth orbit has a radius:
(A) nao
(B) ao/n
(C) n2ao
(D) ao/n2

5.The ionisation energy of the ionised sodium atom Na+10 is :
(A) 13.6 eV
(B) 13.6 x 11 eV
(C) (13.6/11) eV
(D) 13.6 x (112) eV

6.Radius of the second Bohr orbit of a singly ionised helium atom is
(A) 0.53 Ao
(B) 1.06 Ao
(C) 0.265 Ao
(D) 0.132 Ao

7.The potential difference applied to an X-ray tube is increased. As a result, in the emitted radiation:
(A) the maximum wavelength increases
(B) the minimum wave length increases
(C) the minimum wavelength remains unchanged
(D) the minimum wave length decreases

8.A beam of electrons accelerated by a large potential difference V is made to strike a metal target to produce X-rays. For which of the following values of V, the resulting X-rays have the lowest minimum wave length:

(A) 10 KV
(B) 20 KV
(C) 30 KV
(D) 40 KV

9.The X-ray beam emerging from an X-ray tube
(A) is monochromatic
(B) contains all wavelengths smaller than a certain maximum wavelength
(C) contains all wave lengths larger than a certain minimum wavelength
(D) contains all wave lengths lying between a minimum and a maximum wavelength.

10.The relation between half-life T of a radioactive sample and its mean life τ is:
(A) T = 0.693 τ
(B) τ = 0.693 T
(C) τ = T
(D) τ = 2.718 T