Check important MCQs (with solutions) for CBSE Class 12th Physics Board Exam 2020 (Chapter 11 - Dual Nature of Radiation & Matter). Here you will also get important links to access some important articles for the preparation of CBSE 12th board exams 2020. Students preparing for CBSE Class 12th Physics Board Exam usually ask about important MCQs (Multiple Choice Questions) & here, we have provided important questions (with answers), based on Chapter 11 (Dual Nature of Radiation and Matter) of Class 12th Physics NCERT textbook.

**CBSE Sample Papers 2020 for 10th & 12th with Answers & Marking Schemes: All Subjects**

**NCERT Exemplar Solutions for CBSE Class 12 Physics**

**Important MCQs for CBSE Class 12 Physics Board Exam 2020 (Chapter 11 - Dual Nature of Radiation and Matter):**

**Q1.** In a plot of the kinetic energy of the emitted photo electrons from a metal verses the frequency of the incident radiation gives a straight line whose slope

(a) depends on the nature of the metal used

(b) depends on the intensity of the radiation

(c) is the same for all metals and independent of the intensity of the radiation

(d) depends both on the intensity of the radiation and the metal used

**Sol:** (c)

We know that, Einstein photoelectric equation is given by, (K.E.) _{max} = h*v* ‒*Φ*_{o}. This equation is similar to equation of straight line *y* = *mx* + *c*. Thus the graph between K.E. and frequency v is a straight line whose slope (*m*) is equal to Planck’s constant (*h*).

**Q2.** The velocity of the most energetic electrons emitted from a metallic surface is doubled when the frequency (*v*) of incident radiation is double. What is the work function of this metal?

(a) zero

(b) hv/3

(c) hv/2

(d) 2hv/3

**Sol:** (d)

Using Einstein’s photoelectric equation, we have

**Q3.** When light of wavelength λ strikes a photo sensitive surface, then the kinetic energy of ejected electrons is E. If the kinetic energy is to be changed to 2E then the wavelength should be changed to λ^{’}. The correct relation between λ and λ^{’} is

(a) λ^{’} = λ

(b) λ^{’} =2 λ

(c) λ/2 < λ^{’}< λ

(d) λ^{’} = λ/2

**Sol:** (c)

According to the question,

The two relations will be satisfied if λ’ > λ/2 and λ’ < λ.

**Q4.** *K _{1}* and

*K*are maximum kinetic energies of photo electrons emitted when light having wavelengths λ

_{2}_{1}and λ

_{2}respectively incident on a metallic surface. If λ

_{1}= 3λ

_{2}, then

(a) K_{1} < (K_{2}/3)

(b) K1 > (K_{2}/3)

(c) K_{1} = 3K_{2}

(d) None of these

**Sol:** (a)

**Q5.** The ratio of momenta of an electron and an alpha particle which are accelerated from rest through a potential different of 100 volt is

**Sol:** (d)

**Q6.** The energy of photon is equal to the K.E. of a proton. The energy of the photon is E. Let λ_{1} be the de- Broglie wavelength of the proton and be the wavelength of the photon. The ratio λ_{1}/ λ_{2} is proportional to

(a) *E*^{o}

(b) *E*^{1/2}

(c) *E*^{-1}

(d) *E*^{-1/2}

**Sol:** (b)

**Q7.** In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by

(a) increasing the potential different between the anode and filament

(b) increasing the filament current

(c) decreasing the filament current

(d) decreasing the potential difference between the anode and filament

**Sol:** (d)

If, *e* is the charge on electron, *V* is the potential difference, *m* is the mass of the particle and *v *is the velocity of the particle then, eV = 1/2mv^{2} or vα √V

Therefore, velocity of electron emitted from electron gun can be increased by increasing the potential difference between anode and filament in Davisson and Germer experiment.

**Q8.** In Davisson – Germer experiment, if the angle of diffraction is 52^{o}, then the glancing angle will be:

(a) 32^{o}

(b) 64^{o}

(c) 72^{o}

(d) 92^{o}

**Sol:** (b)

Glancing angle, θ = 90° - ∅/2 = 90° – 52/2 = 64°

**Q9.** The Davisson-Germer experiment demonstrated the

(a) particle nature of electron

(b) wave nature of electron

(c) wave nature of photon

(d) particle nature of

**Sol:** (a)

Davisson-Germer experiment established the wave nature of slow moving electrons.

**Q10.** If λ_{0} and *v*_{o} are threshold wavelength and frequency, then for a light having wavelength λ and frequency *v*_{o} the photoelectric effect will take place if

(a) λ < λ_{o}

(b) *v *> *v*_{o}

(c) both (a) and (b)

(d) none of these

**Sol:** (c)

Photoelectric emission will take place if λ < λ_{o} ,* v *> *v*_{o}.

## Comments