Dual Nature of Matter and Radiation MCQs for NEET

Following are a few important definitions that one has to deal with while studying the dual nature of matter and radiation:

• Work Function – The minimum energy required by an electron to escape from the metal surface is known as the work function of the metal.
• Thermionic emission – The electrons emitted from the metal surface of the metal with the help of thermal energy.
• Stopping Potential – The value of the retarding potential at which the photoelectric current becomes zero is known as the stopping potential.
• Threshold frequency – The minimum value of the frequency of incident radiation below which the photoelectric emission stops altogether is called threshold frequency.

Question and Answer

1. Light of frequency 1.9 times the threshold frequency is incident on a photosensitive material. If the frequency is halved and intensity is doubled, the photocurrent becomes

1. doubled
2. quadrupled
3. halved
4. zero

Answer: (d) zero

2. For a metal having a work function W_0, the threshold wavelength is λ. What is the threshold wavelength for the metal having work function 2W0?

1. λ/4
2. λ/2
3. 2λ
4. 4λ

Answer: (b) λ/2

3. Radiation of frequency ν is incident on a photosensitive metal. When the frequency of the incident radiation is doubled, what is the maximum kinetic energy of the photoelectrons?

1. 4E
2. 2E
3. E + hν
4. E – hν

Answer: (c) E + hν

4. How does the maximum kinetic energy of a photoelectron vary with the frequency (v) of the incident radiation?

Answer: (b)

5. The stopping potential V₀ for photoelectric emission from a metal surface is plotted along with the y-axis and frequency v of incident light along the x-axis. A straight line is obtained as shown. Planck’s constant is given by

1. product of the slope of the line and charge on the electron
2. intercept along y-axis divided by the charge on the electron
3. product of the intercept along x-axis and mass of the electron
4. the slope of the line

Answer: (a) product of the slope of the line and charge on the electron

6. Calculate the de Broglie wavelength associated with the electron which has a kinetic energy of 5 eV.

1. 5.47 Å
2. 2.7 Å
3. 5.9 Å
4. None of the above

Answer: (a) 5.47 Å

7. What is the ratio of the de Broglie wavelengths proton and an α particle if they are accelerated by the same potential difference?

1. 2√2: 1
2. 3:2
3. 3√2: 1
4. 2: 1

Answer: (a) 2√2: 1

8. Which of the following graphs represent the variation of particle momentum associated with de Broglie wavelength?

Answer: (c)

9. By what factor will the de Broglie wavelength change if the K.E if the free electron is doubled?

1. ½
2. \(\begin{array}{l}\frac{1}{\sqrt{2}}\end{array} \)
3. 2
4. \(\begin{array}{l}{\sqrt{2}}\end{array} \)

Answer: (b)

10. In photoelectric effect what determines the maximum velocity of the electron reacting with the collector?

1. Frequency of incident radiation alone
2. The potential difference between the emitter and the collector
3. The work function of metal
4. All of these

Answer: (d) All of these

11. Who among the following established that electric charge is quantised?

1. R.A. Millikan
2. Wilhelm Rontgen
3. William Crookes
4. J.J. Thomson

Answer: (a) R.A. Millikan

12. By which of the following physical processes can minimum energy required for the electron emission from the metal surface be supplied to the free electrons?

1. Field emission
2. Thermionic emission
3. Photoelectric emission
4. All of these

Answer: (d) All of these

13. Which of the following statements is true regarding the photoelectric experiment?

1. The stopping potential increases with the increase in the intensity of incident light.
2. The photocurrent increases with the intensity of light.
3. The photocurrent increases with the increase in frequency
4. All of the above

Answer: (b) The photocurrent increases with the intensity of light.

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