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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.
Answer
Answer: (c) the wavelength of radiation should be decreased.
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
Answer
Answer: (b) 10-9 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
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
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
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
Answer
Answer: (a) 3 × 10-19
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
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
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.
Answer
Answer: (d)
Question 10.
The best metal to be used for photoemission is:
(a) Potassium
(b) Lithium
(c) Sodium
(d) Cesium
Answer
Answer: (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
Answer
Answer: (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
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
Answer
Answer: (a) & (b)
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
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
Answer
Answer: (c) Zero
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
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
Answer
Answer: (b) 150 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
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
Answer
Answer: (a) & (c)
Question 20.
The magnification produced by electron microscope is of the order of:
(a) 10
(b) 105
(c) 10³
(d) 107
Answer
Answer: (b) 105
Fill in the Blanks
Question 1.
Stopping potential is the measure of the ………………… of the photoelectrons and does not depend upon …………………
Answer
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.
Answer
Answer: Frequency, intesity.
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
Answer: h(\(\frac {1}{λ}\) – \(\frac {1}{λ_0}\))
Question 4.
The stopping potential depends upon ………………… of incident light and ………………… of metal.
Answer
Answer: freqeuncy, work function.
Question 5.
The maximum kinetic energy of emitted electrons in photoelectric effect is linearly dependent on the ………………… of the incident radiation.
Answer
Answer: freqeuncy.
Question 6.
The mass of a moving photon is …………………
Answer
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 …………………
Answer
Answer: 3hv0
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.
Answer
Answer: 6 × 10-4 NC-1.
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
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 …………………
Answer
Answer: Zero.
Question 11.
A photon behaves as if it had a mass equal to ………………… and momentum equal to …………………
Answer
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 …………………
Answer
Answer: 1.23 Å.
Question 13.
An electron is accelerated through a potential difference of 104 V. The energy acquired by the electron is …………………
Answer
Answer: 1.6 × 10-15 J
Question 14. Out of proton, neutron, ß-particle and a-particle ………………… will have the maximum de-Broglie wavelength.
Answer
Answer: ß particle.
Question 15.
If electrons photons are considered to be of same de- Broglie wavelength, then they will have the same …………………
Answer
Answer: momentum
Question 16.
If a photon and an electron ate considered to be of same de-Broglie wavelength, then the velocity of photon is …………………
Answer
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
Answer: \(\sqrt{\frac {2eV}{m}}\)
Question 18.
The mass of a photon at rest is …………………
Answer
Answer: zero.
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
Answer: 1 eV.
Question 20.
Einstein’s photoelectric equation is expressed as …………………
Answer
Answer: hv = ω0 + \(\frac {1}{2}\) mv².
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