CBSE Class 12 Physics Dual Nature Of Matter And Radiation Worksheet Set B

CBSE Class 12 Physics Dual nature of radiation Atoms and Nuclei.Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects. 

1 What is the stopping potential applied to a a photocell if the maximum kinetic energy of a photoelectron is 5eV ?

2 Work functions of two metals A and B are 4eV and 10 eV respectively . Which metal has the higher threshold wavelength ?

3 Two beams ,one of red light and the other of blue light , of same intrensity incident on a metallic surface to emit Photoelectrons. Which one of them emits electrons of greater kinetic energy?

4 How does the stopping potential of a Photo cell change ,when i) the intensity of the incident radiation is halved? Ii) frequency of incident radiation increases ?

5 If the potential difference used to accelerate electrons is tripled , by what factor the de Broglie wavelength of electron beam change?

6 An electron and proton have the same kinetic energy .Which one of them has the larger de Broglie wavelength.

7 An alpha particle and a proton are accelerated from rest by the same potential. Find the ratio of their de Broglie wavelengths.

8 Show graphically the variation of de Broglie wavelength λ of an electron with i)√V ii) V where V is the potential through which an electron is accelerated from rest.

9 Name the experiment which verified the wave nature of electrons.

Which phenomenon was observed in this experiment using an electron beam?

10 Why Caesium oxide is coated on the cathode of Photo electric cell?

Important Questions for NCERT Class 12 Physics Dual Nature Of Matter And Radiation 

Question. The stopping potential doubles when the frequency of the incident light changes from n to 3v/2. Then the work function of the metal must be    
(a) hν/2
(b) hν
(c) 2hν
(d) none of the above

Answer : A

Question. The force on a hemisphere of radius 1 cm if a parallel beam of monochromatic light of wavelength 500 nm. falls on it with an intensity of 0.5 W/cm2, striking the curved surface in a direction which is perpendicular to the flat face of the hemisphere is (assume the collisions to be perfectly inelastic)    
(a) 5.2 × 10^–13 N
(b) 5.2 × 10^–12 N
(c) 5.22 × 10^–9 N
(d) zero

Answer : C

Question. A 15.0 eV photon collides with and ionizes a hydrogen atom. If the atom was originally in the ground state (ionization potential =13.6 eV), what is the kinetic energy of the ejected electron?    
(a) 1.4 eV
(b) 13.6 eV
(c) 15.0 eV
(d) 28.6 eV

Answer : A

Question. A beam of cathode rays is subjected to crossed electric (E) and magnetic fields (B). The fields are adjusted such that the beam is not deflected. The specific charge of the cathode rays is given by   
(a)  B²/2VE²
(b) 2VB²/E²
(c) 2VE²/B²
(d) E²/2VB²
(Where V is the potential difference between cathode and anode)

Answer : D

Question. In the phenomenon of electric discharge through gases at low pressure, the coloured glow in the tube appears as a result of
(a) collisions between the charged particles emitted from the cathode and the atoms of the gas
(b) collision between different electrons of the atoms of the gas
(c) excitation of electrons in the atoms
(d) collision between the atoms of the gas. 

Answer : A

Question. In a discharge tube ionization of enclosed gas is produced due to collisions between
(a) neutral gas atoms/molecules
(b) positive ions and neutral atoms/molecules
(c) negative electrons and neutral atoms/molecules
(d) photons and neutral atoms/molecules. 

Answer : C

Question. J.J. Thomson’s cathode-ray tube experiment demonstrated that
(a) cathode rays are streams of negatively charged ions
(b) all the mass of an atom is essentially in the nucleus
(c) the e/m of electrons is much greater than the e/m of protons
(d) the e/m ratio of the cathode-ray particles changes when a different gas is placed in the discharge tube 

Answer : C

Question. Which of the following is not the property of cathode rays ?
(a) It produces heating effect.
(b) It does not deflect in electric field.
(c) It casts shadow.
(d) It produces fluorescence.

Answer : B

Question. Who evaluated the mass of electron indirectly with help of charge?
(a) Thomson
(b) Millikan
(c) Rutherford
(d) Newton 

Answer : A

Question. In a discharge tube at 0.02 mm, there is formation of
(a) Crooke’s dark space
(b) Faraday’s dark space
(c) both space partly
(d) none of these.

Answer : A

Question. In which of the following, emission of electrons does not take place
(a) thermionic emission
(b) X-rays emission
(c) photoelectric emission
(d) secondary emission 

Answer : B

Question. Thermions are
(a) protons
(b) electrons
(c) photons
(d) positrons

Answer : B

Question. A source of light is placed at a distance of 50 cm from a photo cell and the stopping potential is found to be V0. If the distance between the light source and photo cell is made 25 cm, the new stopping potential will be :
(a) V0/2
(b) V0
(c) 4V0
(d) 2V0

Answer : B

Question. Photoelectric emission occurs only when the incident light has more than a certain minimum
(a) power
(b) wavelength
(c) intensity
(d) frequency 

Answer :  D

Question. A 200 W sodium street lamp emits yellow light of wavelength 0.6 μm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is
(a) 1.5 × 10²⁰
(b) 6 × 10¹⁸
(c) 62 × 10²⁰
(d) 3 × 10¹⁹

Answer: A

Question. A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2 . If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is :
(h = Planck's constant, c = speed of light)
(a) hc/λ
(b) 2hc/λ
(c) hc/3λ
(d) hc/2λ

Answer: D

Question. An electron of mass m and a photon have same energy E.
The ratio of de-Broglie wavelengths associated with them is :
(a) 1/c(E/2m)^1/2
(b) (E/2m)^1/2
(c) c(2mE)^1/2
(d) 1/xc(2m/E)^1/2

Answer: A

Question. The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (Kelvin) and mass m, is :-

Answer: A

Question. Photoelectric work function of a metal is 1eV. Light of wavelength λ = 3000 Å falls on it. The photo electrons come out with velocity
(a) 10 metres/sec
(b) 10² metres/sec
(c) 10⁴ metres/sec
(d) 10⁶ metres/sec

Answer: D

DIRECTIONS : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer from the following-
(a) Statement-1 is false, Statement-2 is true
(b) Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1
(c) Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1
(d) Statement-1 is true, Statement-2 is false

Question. Statement-1 : Photoelectric saturation current increases with the increase in frequency of incident light.
Statement-2 : Energy of incident photons increases with increase in frequency and as a result photoelectric current increases.

Answer: D

Question. Statement-1 : Though light of a single frequency (monochromatic) is incident on a metal, the energies of emitted photoelectrons are different.
Statement-2 : The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

Answer: A

Question. Statement-1 : Photosensitivity of a metal is high if its work function is small.
Statement-2 : Work function = hf₀ where f₀ is the threshold frequency.

Answer: B

Question. Statement-1 : In process of photoelectric emission, all emitted electrons do not have same kinetic energy.
Statement-2 : If radiation falling on photosensitive surface of a metal consists of different wavelength then energy acquired by electrons absorbing photons of different
wavelengths shall be different.

Answer: B

Question. Statement-1 : The de-Broglie wavelength of a molecule (in a sample of ideal gas) varies inversely as the square root of absolute temperature.
Statement-2 : The rms velocity of a molecule (in a sample of ideal gas) depends on temperature.

Answer: A

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