# MCQ Questions for Class 12 Physics Chapter 11 Dual Nature of Radiation and Matter with Answers

### CBSE Class 12 Physics MCQs Solution All Chapters

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### Dual Nature of Radiation and Matter Class 12 Physics MCQs

1. Who established that electric charge is quantised?
(a) J.J. Thomson
(b) William Crookes
(c) R.A. Millikan
(d) Wilhelm Rontgen

2. Cathode rays were discovered by
(a) Maxwell Clerk James
(b) Heinrich Hertz
(c) William Crookes
(d) J.J. Thomson

3. The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by which of the following physical processes?
(a) Thermionic emission
(b) Field emission
(c) Photoelectric emission
(d) All of these

4. The phenomenon of photoelectric emission was discovered in 1887 by
(a) Albert Einstein
(b) Heinrich Hertz
(c) Wilhelm Hallwachs
(d) Philipp Lenard

5. A metal surface ejects electrons when hit by green light but nothing when hit by yellow light. The electrons will be ejected when the surface is hit by
(a) blue light
(b) heat rays
(c) infrared light
(d) red light

6. Which of the following statements is correct regarding the photoelectric experiment?
(a) The photocurrent increases with intensity of light.
(b) Stopping potential increases with increase in intensity of incident light.
(c) The photocurrent increases with increase in frequency.
(d) All of these

7. In photoelectric effect, the photocurrent
(a) depends both on intensity and frequency of the incident light.
(b) does not depend on the frequency of incident light but depends on the intensity of the inci-dent light.
(c) decreases with increase in frequency of inci-dent light.
(d) increases with increase in frequency of inci-dent light.

8. The maximum value of photoelectric current is called
(a) base current
(b) saturation current
(c) collector current
(d) emitter current

9. In photoelectric effect, the photoelectric current is independent of
(a) intensity of incident light
(b) potential difference applied between the two electrodes
(c) the nature of emitter material
(d) frequency of incident light

10. In photoelectric effect, stopping potential depends on
(a) frequency of incident light
(b) nature of the emitter material
(c) intensity of incident light
(d) both (a) and (b)

11. According to Einstein’s photoelectric equation, the graph of kinetic energy of the photoelectron emitted from the metal versus the frequency of the incident radiation gives a straight line graph, whose slope
(a) depends on the intensity of the incident radi-ation.
(b) depends on the nature of the metal and also on the intensity of incident radiation.
(c) is same for all metals and independent of the intensity of the incident radiation.
(d) depends on the nature of the metal.

12. The figure shows stopping V0A potential V0 and frequency o for two different metallic surfaces A and B. The work function of A, as compared to that of B is

(a) less
(b) more
(c) equal
(d) nothing can be said

13. Which phenomenon best supports the theory that matter has a wave nature?
(a) Electron momentum
(b) Electron diffraction
(c) Photon momentum
(d) Photon diffraction

### Dual Nature of Radiation and Matter Class 12 MCQs Questions with Answers

Question 1.
Photoelectrons are being obtained by irradiating zinc by a radiation of 3100 Å. In order to increase the kinetic energy of ejected photoelectrons.
(a) the intensity of radiation should be increased.
(b) the wave length of radiation should be increased.
(c) the wavelength of radiation should be decreased.
(d) both wavelength and intesity of radiation should be increased.

Question 2.
The de-Broglie wavelength of an electron moving with a speed of 6.6 × 1015 ms-1 is nearly equal to
(a) 10-11m
(b) 10-9 m
(c) 10-7 m
(d) 10-5 m

Question 3.
An electron accelerated through a potential difference of V volt has a wavelength λ associated with it, Mass of proton is nearly 2000 times that of an electron. In order to have the same λ for proton, it must be accelerated through a potential difference (in volt) of
(a) V
(b) $$\sqrt{2000}$$ V
(c) 2000V V
(d) $$\frac{V}{2000}$$

Answer: (d) $$\frac{V}{2000}$$

Question 4.
An electron of mass m, when accelerated through a potential difference V, has de-Broglie wavelength λ. The de-Broglie wavelength associated with a proton of mass M and accelerated through the same potential difference will be
(a) λ$$\sqrt{\frac{m}{M}}$$
(b) λ$$\frac{m}{M}$$
(c) λ$$\sqrt{\frac{M}{m}}$$
(d) λ$$\sqrt{\frac{m}{m}}$$

Answer: (a) λ$$\sqrt{\frac{m}{M}}$$

Question 5.
The energy E and momentum p of a photon is given by E = hv h and p = $$\frac{h}{λ}$$. The velocity of photon will be
(a) $$\frac{E}{P}$$
(b) ($$\frac{E}{P}$$)²
(c) $$\sqrt{\frac{E}{P}}$$
(d) (EP)³

Answer: (a) $$\frac{E}{P}$$

Question 6.
Ultra-violet radiation of 6.2 eV falls on an aluminium surface having work-function 4.2 eV. The kinetic energy (in J) of the fastest electron emitted is nearly.
(a) 3 × 10-19
(b) 3 × 10-15
(c) 3 × 10-17
(d) 3 × 10-21

Question 7.
For light of wavelength 5000 Å, the photon energy is nearly 2.5 eV. For X-rays of wavelength 1 Å, the photon energy will be close to:
(a) 2.5 × 5000 eV
(b) 2.5 ÷ 5000 eV
(c) 2.5 × (5000)² eV
(d) 2.5 ÷ (5000)² eV

Answer: (a) 2.5 × 5000 eV

Question 8.
A photocell is illuminated by a small bright source placed 1 metre away. When the same source of light is placed 2 m away, the electrons emitted per sec. (i.e. saturation current in the photo cell is) are
(a) I ∝ 2²
(b) I × $$\frac {1}{4}$$
(c) I ∝ 4
(d) I ∝ $$\frac {1}{2}$$

Answer: (b) I × $$\frac {1}{4}$$

Question 9.
Which one of the following graph represent correctly the variation of maximum kinetic energy Emax with the intensity of incident radiations having a constant frequency.

Question 10.
The best metal to be used for photoemission is:
(a) Potassium
(b) Lithium
(c) Sodium
(d) Cesium

Question 11.
The threshold frequency for a certain metal is v0. When light of frequency v = 2v0 is incident on it, the maximum velocity of photo electrons is 4 × 106 ms-1. If the frequency of incident radiation is increased to 5 v0, then the maximum velocity of photo electrons (m/s) is
(a) 8 × 105
(b) 2 × 106
(c) 2 × 107
(d) 8 × 106

Question 12.
The frequency and the intensity of a beam of light falling on the surface of photoelectric material are increased by a factor of two. This will:
(a) increase the maximum K.E. of photo-electron as well as photoelectric current by a factor of two.
(b) increase maximum K.E. of photoelectrons and would increase the photo current by a factor of two.
(c) increase the maximum K.E. of photo electrons by a factor of two and will no affect photoelectric current.
(d) No effect on both maximum K.E. and photoelectric current.

Answer: (b) increase maximum K.E. of photoelectrons and would increase the photo current by a factor of two.

Question 13.
Which of the following is not the property of photons
(a) charge
(b) rest mass
(c) energy
(d) momentum

Question 14.
Dynamic mass of photon of wavelength k is
(a) Zero
(b) $$\frac {hc}{λ}$$
(c) $$\frac {h}{cλ}$$
(d) $$\frac {h}{2λ}$$

Answer: (c) $$\frac {h}{cλ}$$

Question 15.
The time required in emitting photo electrons is
(a) 10-8 s
(b) 10-4 s
(c) Zero
(d) 1 sec

Question 16.
When light is directed at the metal surface, the emitted electrons:
(a) are called photons
(b) have energies that depend upon the intensity of light.
(c) have random energies.
(d) have energies that depend upon the frequency of light.

Answer: (d) have energies that depend upon the frequency of light.

Question 17.
The wavelength associated with n electron is 1Å. The potential difference required for accelerating it is
(a) 100 V
(b) 150 V
(c) 250 V
(d) 10³ V

Question 18.
The momentum of a photon is 10-27 kg ms-1. Its energy will be:
(a) 3 × 10-19 J
(b) 3 × 10-34 j
(c) 3 × 10-27 J
(d) none of these

Answer: (a) 3 × 10-19 J

Question 19.
With which of the following particles moving with same velocity de-Broglie wave length will be maximum?
(a) ß-particle
(b) ∝ particle
(c) electron
(d) proton

Question 20.
The magnification produced by electron microscope is of the order of:
(a) 10
(b) 105
(c) 10³
(d) 107

Fill in the Blanks

Question 1.
Stopping potential is the measure of the ………………… of the photoelectrons and does not depend upon …………………

Answer: Maximum kinetic energy, intensity of incident light.

Question 2.
In photoelectric effect experiment, photo electric current does not depend upon ………………… but depends only on the ………………… of incident reduction.

Question 3.
The threshold wavelength of a photo cathode to emit photoelectrons is λ0. When a radiation of wavelength λ is incident on it, the average K.E. of the photoelectron is …………………

Answer: h($$\frac {1}{λ}$$ – $$\frac {1}{λ_0}$$)

Question 4.
The stopping potential depends upon ………………… of incident light and ………………… of metal.

Question 5.
The maximum kinetic energy of emitted electrons in photoelectric effect is linearly dependent on the ………………… of the incident radiation.

Question 6.
The mass of a moving photon is …………………

Answer: $$\frac {h}{cλ}$$

Question 7.
The photoelectric threshold frequency of a metal is v0. When light of frequency uv0 is incident on the metal, the maximum kinetic energy of the emitted photoelectron is …………………

Question 8.
An electron beam passes at right angles to a magnetic field of 2 × 10-3 Wb m-2. The speed of the electron is 3 × 107 ms-1 An electric field of ………………… intensity should be applied along with the magnetic field so that the path of the electron beam remains indeviated.

Question 9.
An electron, photon, a neutron are accelerated through the same potential difference. The kinetic energies acquired by them will be in the ratio …………………

Answer: 1 : 1 : 1.

Question 10.
Light of frequency 1.5 times the threshold frequency is incident on a photo sensitive material. If the frequency of incident light is halved and the intensity is doubled, the photo current becomes …………………

Question 11.
A photon behaves as if it had a mass equal to ………………… and momentum equal to …………………

Answer: $$\frac {hv}{c^2}$$, $$\frac {hv}{c}$$

Question 12.
An electron is accelerated through a potential difference of 100 V. The wavelength associated with it is …………………

Question 13.
An electron is accelerated through a potential difference of 104 V. The energy acquired by the electron is …………………

Question 14. Out of proton, neutron, ß-particle and a-particle ………………… will have the maximum de-Broglie wavelength.

Question 15.
If electrons photons are considered to be of same de- Broglie wavelength, then they will have the same …………………

Question 16.
If a photon and an electron ate considered to be of same de-Broglie wavelength, then the velocity of photon is …………………

Answer: greater than that of the electron.

Question 17.
An electron of mass m and charge e is accelerated from rest through a potential difference of V in vacuum. Its final velocity will be …………………

Answer: $$\sqrt{\frac {2eV}{m}}$$

Question 18.
The mass of a photon at rest is …………………

Question 19.
When a proton is accelerated through a potential difference of one volt, the kinetic energy gained by it is roughly equal to …………………

Answer: hv = ω0 + $$\frac {1}{2}$$ mv².