# MCQ | Modern Physics

QUIZ TEST-I

Question: 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) 1.825eV

Ans: (C)

Question: 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

Ans: (C)

Question: 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

Ans: (A)

Question: 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

Ans: (C)

Question: 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

Ans: (D)

Question: 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

Ans: (B)

Question: 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

Ans: (D)

Question: 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

Ans: (D)

Question: 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.

Ans: (C)

Question: 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

Ans: (A)

Question: 11.  The stopping potential for the photo electrons emitted from a metal surface of work function 1.7 eV is 10.4 V. Identify the energy levels corresponding to the transitions in hydrogen atom which will result in emission of wavelength equal to that of incident radiation for the above photoelectric effect

(A) n = 3 to 1

(B) n = 3 to 2

(C) n = 2 to 1

(D) n = 4 to 1

Ans: (A)

Question: 12.  An electron collides with a fixed hydrogen atom in its ground state. Hydrogen atom gets excited and the colliding electron loses all its kinetic energy. Consequently the hydrogen atom may emit a photon corresponding to the largest wavelength of the Balmer series. The K.E. of colliding electron will be

(A) 10.2 eV

(B) 1.9 eV

(C) 12.1 eV

(D) 13.6 eV

Ans: (C)

Question: 13.  When a radioactive isotope 88Ra228 decays in series by the emission of three α-particles and a β particle the isotope finally formed is :

(A) 84X220

(B) 86X222

(C) 83X216

(D) 83X215

Ans: (C)

Question: 14. Photo electric effect supports the quantum nature of light because:

(A) there is a minimum frequency of light below which no photo electrons are emitted.

(B) the maximum K.E. of photoelectrons depends only on the frequency of light and not on its intensity.

(C) even when the metal surface is faintly illuminated by light of the approximate wavelength, the photo electrons leave the surface immediately.

(D) electric charge of photoelectrons is quantized.

Ans: (C)

Question: 15.  If the electron in the hydrogen atoms is excited to n = 5 state, the number of frequencies present in the radiation emitted is :
(A) 4

(B) 5

(C) 8

(D) 10

Ans: (D)

Question: 16. The ratio of magnetic dipole moment of an electron of charge e and mass m in the Bohr orbit in hydrogen to the angular momentum of the electron in the orbit is:

(A) e/m

(B) e/2m

(C) m/e

(D) 2m/e

Ans: (B)

Question: 17.  The wave length λ of Kα-ray line of an anticathode element of atomic number Z is nearly proportional to:

(A) Z2

(B) (Z – 1)2

(C) 1/(Z – 1)

(D) 1/(Z – 1)2

Ans: (D)

Question: 18. If λ1 and λ2 are the wavelengths of characteristic X-ray and gamma rays respectively, then the relation between them is :

(A) λ1 ≤ λ2

(B) λ1 = λ2

(C) λ1 > λ2

(D) λ1 < λ2

Ans: (C)

Question: 19. In the nuclear reaction given by 2He4 + 7N141H1 + X then the nucleus X is :

(A) Nitrogen of mass 16

(B) Nitrogen of mass 17

(C) Oxygen of mass 16

(D) Oxygen of mass 17

Ans: (D)

Question: 20. If 10% of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is approximately:

(A) 60%

(B) 65%

(C) 70%

(D) 75%