# CBSE Board Exam 2020: Important MCQs (with Answers) for Class 12 Physics - Chapter 11 - Dual Nature of Radiation and Matter; Also useful for JEE Main, UPSEE, WBJEE & Other Engineering Entrance Exams

Learn important MCQs (with Answers) for Class 12 Physics Board Exam 2020 (Chapter 11 - Dual Nature of Radiation and Matter). These MCQs are very useful for other competitive exams like UPSEE 2020, JEE Main 2020, WBJEE 2020 etc.

Created On: Feb 6, 2020 12:33 IST
Modified On: Feb 6, 2020 14:06 IST CBSE Class 12 Physics Board Exam Important MCQ Chapter 11 Dual Nature of Radiation and Matter

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 = hvΦo. 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. K1 and K2 are maximum kinetic energies of photo electrons emitted when light having wavelengths λ1 and λ2 respectively incident on a metallic surface. If λ1 = 3λ2, then

(a) K1 < (K2/3)

(b) K1 > (K2/3)

(c) K1 = 3K2

(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 λ1  be the de- Broglie wavelength of the proton and  be the wavelength of the photon. The ratio λ1/ λ2 is proportional to

(a) Eo

(b) E1/2

(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 = 1/2mv2 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 52o, then the glancing angle will be:

(a) 32o

(b) 64o

(c) 72o

(d) 92o

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 λ0 and vo are threshold wavelength and frequency, then for a light having wavelength λ  and frequency vo the photoelectric effect will take place if

(a) λ < λo

(b) v > vo

(c) both (a) and (b)

(d) none of these

Sol: (c)

Photoelectric emission will take place if λ < λo , v > vo.

NCERT Exemplar Solutions for CBSE Class 12 Physics

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