Class 12 Physics
Dual Nature Of Radiation and Matter
Very Short Questions Answers
Answer: Kinetic Energy (K) = p²/2m
where p = momentum and m = mass.
∴ p = √2mK
∴ de-Broglie wavelength λ = h/p = h/ √2mK
Q2: Mention one physical process for the release of an electron from the surface of a metal?
Answer: Photoelectric emission.
Q3: Name an experiment which shows the wave nature of the electron. Which phenomenon was observed in this experiment using an electron beam?
Answer: Davisson-German experiment shows the wave nature of the electron. Phenomena of constructive interference were observed in the Davisson-Germer experiment.
Q4: What is Thermionic emission?
Answer: It is the phenomenon of emission of electrons from the metal surface when heated suitably.
Q5: Ultraviolet light is incident on two photosensitive materials having work function ϕ₁ and ϕ₂(ϕ₁ >ϕ₂). In which of the case will K.E. of emitted electrons be greater? Why?
Answer: hv = ϕₒ + KE
If ϕ₁ >ϕ₂, K.E. will be more for the second surface whose work function is less.
Q6: What consideration led de-Broglie to suggest that material particles can also show wave property?
Answer: Nature loves symmetry and matter can be converted into energy and vice- versa, i.e., matter and energy are two forms of the same entity.
Q7: What is photoelectric emission?
Answer: It is the phenomenon of emission of electrons from the surface of the metal when light radiations of suitable frequency fall on it.
Q8: How does the stopping potential apply to a photocell change if the distance between
the light source and the cathode of the cell are doubled?
Answer: Stopping potential does not depend on the intensity of the light source which changes
due to the change in distance from the light source.
Q9: If an electron behaves like a wave, what should determine the wavelength and frequency of this wave.
Answer: Momentum and Energy
Q10: Is there any difference between light waves and matter waves?
Answer: Yes, the velocity of light waves in a vacuum is constant, whereas the velocity of matter waves in a vacuum depends upon the wavelength of a matter wave.
Q11: What is the Photoelectric effect?
Answer: It is the phenomenon of emission of electrons from the surface of metals when light radiations of suitable frequency fall on them.
Q12: Why is photoelectric emission not possible at all frequencies?
Answer: Photoelectric emission is not possible at all frequencies because below the threshold frequency for a photosensitive surface of different atoms emission is not possible.
Q13: On what factor does the retarding potential of a photocell depend?
Answer: It depends upon the frequency of the incident light.
Q14: What are photons?
Answer: These are the packets of energy (or energy particles) which are emitted by a source of radiation. The photons emitted from a source, travel through space with the same speed c (equal to the speed of light).
Q15: State de-Broglie Hypothesis?
Answer: de Broglie hypothesis states that atomic particles of matter moving with a given velocity, (or
momentum) can display wave-like properties.
Q16: What is Stopping Potential?
Answer: It is that minimum negative potential given to anode in a photocell for which the photoelectric current becomes zero. It is denoted by Vₒ. It is independent of the intensity of the incident light.
See also:
Ch 1: Electric Charge and Fields (VSQA)
Electrostatics - Important Theory Questions
Ch 2: Electrostatic Potential and Capacitance (Short Q and A)
Ch 3: Current Electricity - (NCERT Solutions)
Ch 3: Current Electricity - Important Theory Questions
Ch 4: Moving Charges and Magnetism (VSQA)
Chapter - Magnetic Effect Of Current (Theoretical Questions)
Ch: Electromagnetic Induction (EMI) (Important Theory Questions)
Chapter - Electromagnetic Waves (Important Theory Questions)
Ch9 - Ray Optics (Important Theory Questions)
Ch 9 - Ray Optics and Optical Instruments (VSQA)
Light - Reflection From Mirrors (Worksheet)
Ch: Wave Optics (Important Theory Questions)
Ch - Electronic Devices (Revision Sheet)
Ch - Atoms and Nuclei - Cathode Rays and Properties
Electromagnetic Waves - About Electromagnetic Spectrum
Physics Sample Question Paper (2015)
Physics Sample Question Paper and Marking Scheme (2016)
Physics Sample Question Paper (2016-17) (See also Marking Scheme of SQP 2016-17)
Physical Constants
Types of Vectors
Simple Physics Quiz
