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NCERT Questions for Class 12 Physics Chapter 11 – Dual Nature of Radiation and Matter
NCERT Class 12 Physics Chapter 11 – Dual Nature of Radiation and Matter important questions is very important for students preparing for their board exams. Students are exposed to the interesting idea of the Dual Nature of Radiation and Matter in this chapter. Albert Einstein was the first to propose this idea, which transformed physics and has major implications for how we understand the universe. These crucial questions have been created by experienced physics teachers using the most recent editions of the NCERT textbooks.
Table of Contents
Important Questions with Solutions of Class 12 Physics Chapter 11 – Dual Nature of Radiation and Matter
Short Answer Questions
1) Suppose that a metal plate experiences radiation at a frequency higher than its threshold frequency. What changes might result from doubling the incident radiation?
- Electron kinetic energy
- Current generated by photoelectric
Ans – (a) When the incident radiation frequency doubles, kinetic energy increases because hv−hv∘ increases as well.
(b) The number of photoelectrons, or photoelectronic current, will remain unchanged if the incident radiation frequency is doubled.
2) An electromagnetic wave with wavelength λ strikes a photosensitive surface characterised by a negligible work function. The emitted photoelectrons from this surface possess a de Broglie wavelength denoted as λ1. Show that
Ans – The energy balance equation of the photoelectric effect is,
hv = ϕ + K.E
For a metal exhibiting a work function of zero
Thus we get,
3) The light of frequency 8×1014 Hz is illuminated on a surface, photoelectrons emitted from it are having a maximum velocity of 7×105 m/s. Determine the threshold frequency for the given surface.
Ans –
3 Mark Questions
1) The solar energy flux incident on the Earth’s surface is 1.388×103 W/m2. What is the approximate number of photons per square metre that strike the Earth each second? Assume that the photons in sunlight possess an average wavelength of 550 nm.
Ans – The energy flux is the rate of energy incident on the Earth’s surface per unit area. It is equivalent to the product of the energy of each photon and their rate of occurrence.
Energy flux P = 1.388 × 103
λ = 550 x 109
P = E × N, where N is the no. of photons per unit area
2) What is the threshold wavelength in the context of the photoelectric effect? The de Broglie wavelength corresponding to an electron subjected to a potential difference V is λ. What will the new wavelength be when the accelerating potential is raised to 4V?
Ans – The threshold wavelength is the highest wavelength of radiation required to produce photoelectric emission.
The new wavelength is therefore half of the old one.
5 Marks Questions
1) X-rays or electrons accelerated by the right voltage can be used in crystal diffraction experiments. Which probe possesses larger energy? For quantitative comparison, set the probe wavelength to 1 Å, which approximates the interatomic spacing within the lattice. me = 9.11 × 10-31 kg
Ans – An X-ray probe possesses greater energy than an electron probe at the same wavelength.
The wavelength of light emitted from the probe is λ = 1 Å = 10-10 m.
The mass of an electron, me, is 9.11 × 10−31 kg.
The constant of Planck, h = 6.6 × 10−34 Js
The charge of an electron, e, is 1.6 × 10−19 C.
The electron’s kinetic energy is expressed as follows:
v = Velocity of the electron
mev = Momentum (p) of the electron
The de Broglie principle states that the de Broglie wavelength is expressed as:
Therefore, a photon possesses greater energy than an electron at the same wavelength.