CBSE Class 12 Physics 2024-25: Unit 6 Dual Nature of Radiation and Matter Competency-Based Questions with Answers; Download Free PDF

As the CBSE Class 12 board exams get closer, it’s important for students to understand the new exam pattern. Starting in the 2024-25 school year, CBSE will include 50% more competency-based questions. These questions will be both multiple choice and written, focusing on how to use what students have learned in real-life situations.

For Class 12 Physics, Unit - 6 on Dual Nature of Radiation and Matter, CBSE has provided competency-based questions that help improve understanding and application skills. It highlights key competency-based questions and provides answers to help students succeed. These questions are designed to help students strengthen their understanding and apply concepts effectively for their exams.

By practicing these competency-based questions, students will get familiar with the types of questions they are likely to face in the exam. The free PDF includes a variety of questions, such as multiple-choice (MCQs) and free-response questions, with answers provided to guide students in their preparation.

CBSE Class 12 Physics Chapter 6 Dual Nature of Radiation and Matter Important Competency-Based Questions

Q1. Select the correct statement regarding photoelectric emission.

A. The number of photoelectrons is proportional to the frequency of the light.

B. The work function of the metal varies as a function of the depth from the surface.

C. Photoelectrons are ejected from the metals only if the incident radiation has a certain minimum wavelength.

D. The photoelectrons produced by a monochromatic incident light incident on the metal surface have a spread of kinetic energies.

Ans. D. The photoelectrons produced by a monochromatic incident light incident on the metal surface have a spread of kinetic energies.

Q2. ASSERTION: A photon is different from a normal particle.

REASON 1: Energy of the photon in motion is purely kinetic as it has no rest energy.

REASON 2: A photon travels with the speed of light in vacuum.

REASON3: Energy of the photon at rest becomes purely potential as its rest mass is zero. Select the correct option.

A. Assertion is correct. Only reason 3 is correct.

B. Assertion is incorrect. Only Reason 2 is correct.

C. Assertion is correct. Only reasons 1 and 2 are correct.

D. Assertion is incorrect. Only Reasons 1 & 3 are correct.

Ans. C. Assertion is correct. Only reasons 1 and 2 are correct.

Q3. Light from a source of frequency f > fo (threshold frequency) is incident on a metal surface. If the intensity of incident radiations from the light source is increased keeping the frequency f of light constant, which of the following quantities associated with emitted photoelectrons DOESNOT remain the same?

A. only photoelectric current

B. only de Broglie wavelength

C. both momentum and maximum KE

D. both de Broglie wavelength and the photo current

Ans. A. only photoelectric current

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Q4. Given are the maximum speeds of the photoelectrons corresponding to a wavelength of incident light on a certain metal surface.

Wave length Maximum speed of the emitted electrons

λ₁ v₁

λ₂ v₂

If v₂ < v₁, then, which of the following is/are CORRECT?

I. Wavelength λ₁ > Wavelength λ₂

II. Frequency f₁ < Frequency f₂

III. Maximum KE due to wavelength λ₁ > Maximum KE due to wavelength λ₂

A. All are correct

B. Only III is correct

C. Only I and II are correct

D. Only II and III are correct

Ans. B. Only III is correct

Q5. A light of wavelength 330 nm causes photoelectric emission from a metal of work function 1 eV. What value of collector potential would stop the photoemission? Take h_c = 1240 eV‐ nm

Ans. Equation:

Φ_o = hν ‐ KE_max = (h c/λ) ‐ KEmax

Here KE_max = eVo where V_o is the stopping potential applied to the collector plate

Φ_o = (h c/λ) ‐ eV_o

[1 mark for the correct relation between work function and collector stopping potential]

[1 mark for the correct calculation ofthe collector potential ]

Q6. A light of wavelength 3000 Angstrom emits photoelectrons of maximum KE of 0.5 eV.

What will be the maximum KE of photoelectrons if the wavelength is changed to 2000 Angstrom? Take hc = 12400 eV‐Å

Ans. Using

In the first case,

Φ_o = (12400/3000) – 0.5

In the second case,

Φ_o = (12400/2000) – K

[0.5 mark for each equation] Equating and solving for K

We get

K = 2.57 eV for wavelength 2000 Å

[1 mark for correct final result]

Q7. A powerful UV laser emits radiation of wavelength 300 nm with a power of 5 mW. Determine the number of photons of this beam that strikes a metal surface every second. Take h_c ~ 2 x 10‐16 J‐nm

Ans. Energy of each photon = h_ν Power of the beam = n h_ν = n h_c/λ

[1 mark for the correct formulae of Energy and power in terms of frequency]

Upon calculating,

n = 7.5 x 10¹⁵ photons per second [1 mark for the correct final result]

Q8. Given are the work functions of two materials.

Material Work function	(eV)
Sodium	2.4
Zinc	4.3

A radiation of wavelength 400 nm is made to fall on each of the above materials. In which of the two materials is the photoelectric emission observed?

Take h = 4.1 × 10^‐15 eV‐s

Ans. Threshold wavelength,

[1 mark for the correct formula for threshold wavelength]

For sodium,

= 5.12 x 10‐7 m = 512 nm

Since the λincident < λthreshold , there will be a photoelectric emission observed in sodium.

[1 mark for the correct calculation and final result]

For Zinc,

= 286 nm

Since the λ_incident > λ_threshold, there will be no photoelectric emission observed in zinc.

[1 mark for the correct calculation and final result]

👉 CBSE Class 12 Study Materials

CBSE Class 12 Syllabus 2024-25	CBSE Class 12 Previous Year Papers
NCERT Books For Class 12 Books	NCERT Class 12 Solutions
CBSE Class 12 Full Study Material	CBSE Class 12 Sample Paper 2024-25