Title 8-modern-physics.pdf ✅

varies as follows. (A) (b) (C) (D) 15. By photoelectric effect, Einstein proved: (A) E = h0 (B) K. E. = 1 2 mv 2 (C) E = mc 2 (D) E = −Rhc 2 n2 16. In a photo-emissive cell, with exciting wavelength λ, the fastest electron has speed v. If the exciting wavelength is changed to 3λ 4 , the speed of the fastest emitted electron will be : (A) less than v(4/3) 1/2 (B) v(3/4) 1/2 (C) v(3/4) 1/2 (D) greater than v(4/3) 1/2 17. According to Einstein's photoelectric equation the plot of the kinetic energy of the emitted photoelectrons from a metal Vs the frequency of the incident radiation gives a straight line whose slope : (A) Depends on the nature of the metal used (B) Depends on the intensity of the radiation (C) Depends both on the intensity of the radiation and the metal used (D) Is the same for all metals and independent of the intensity of the radiation 18. An electron beam has a kinetic energy equal to 100eV. Find its wavelength associated with a beam, if mass of electron = 9.1 × 10−31 kg and 1eV = 1.6 × 10−19 J/eV. (Plank's constant = 6.6 × 10−34JS ) (A) 24.6Å (B) 0.12Å (C) 1.2Å (D) 6.3Å 19. An electron of mass m and charge e is accelerated from rest through a potential difference V in vacuum. Its final velocity will be : (A) √ 2eV m (B) √ eV m (C) eV 2m (D) eV m 20. An electron of mass m, when accelerated through a potential difference V, has de-Broglie wavelength λ. The deBroglie wavelength associated with a proton of mass M accelerated through the same potential difference, will be : (A) λ M m (B) λ m M (C) λ√ M m (D) λ√ m M 21. The time taken by a photoelectron to come out after the photon strikes is approximately : (A) 10−4 s (B) 10−10 S (C) 10−16 s (D) 10−1 s 22. The wavelength of a 1keV photon is 1.24 × 10−9 m. What is the frequency of 1MeV proton?
(A) 1.24 × 1015 (B) 2.4 × 1020 (C) 1.24 × 1018 (D) 2.4 × 1023 23. The work function of a substance is 4.0eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately : (A) 540 nm (B) 400 nm (C) 310 nm (D) 220 nm 24. The momentum of a photon of an electromagnetic radiation is 3.3 × 10−29 kg ms−1 . What is the frequency of the associated waves? [h = 6.6 × 10−34Js; c = 3 × 108 ms−1 ] (A) 1.5 × 1023 Hz (B) 7.5 × 1012 Hz (C) 6 × 103 Hz (D) 9 × 10−32 Hz 25. Hydrogen ( 1H 1 ), deuterium ( 1H 2 ), singly ionized helium ( 2He4 ) +and doubly ionized lithium ( 3Li8 ) ++all have one electron around the nucleus. Consider an electron transition from n = 2 to n = 1. If λ1, λ2, λ3 and λ4 respectively for four elements, then approximately which one of the following is correct? (A) 4λ1 = 2λ2 = 2λ3 = λ4 (B) λ1 = 2λ2 = 2λ3 = λ4 (C) λ1 = λ2 = 4λ3 = 9λ4 (D) λ1 = 2λ2 = 3λ3 = 4λ4 26. The electric potential between a proton and an electron is given by V = V0ln r r0 , where r0 is a constant. Assuming Bohr's model to be applicable, what is the variation of rn with n, (n being the principal quantum number)? (A) rn ∝ n (B) rn ∝ 1 n (C) rn ∝ n 2 (D) rn ∝ 1 n2 27. Radiations of wavelength 180 nm ejects photo- electrons from a plate whose work functions is 2.0eV. If a uniform magnetic field of flux density 5.0 × 10−5 tesla is applied parallel to the plate, what should be the radius of the path followed by electrons ejected normally from the plate with maximum energy? (A) 0.2 m (B) 0.148 m (C) 0.048 m (D) 0.418 m 28. A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 1 2 m away, the number of electrons emitted by photocathode would : (A) Decrease by a factor of 4 (B) Increase by a factor of 4 (C) Decrease by a factor of 2 (D) Increase by a factor of 2 29. The de-Broglie wave corresponding to a particle of mass m and velocity v has a wavelength associated with it : (A) h mv (B) hmv (C) mh v (D) m hv 30. In the spectrum of hydrogen, the ratio of the longest wavelength in Lyman series to the longest wavelength in the Balmer series is : (A) 27 5 (B) 5 27 (C) 4 9 (D) 9 4 31. In radius of the 13 27Al nucleus is taken to be RAl, then the radius of 53 125Te nucleus is nearly : (A) 3 4 RAl (B) ( 23 53) 1/3 RAl (C) ( 53 13) 1/3 RAl (D) 5 3 RAl 32. Consider 3 rd orbit of He+(Helium), using non- relativistic approach, the speed of electron in this orbit will be : [Given K = 9 × 109 constant, Z = 2 and h (Plank's Constant) = 6.6 × 10−34Js ] : (A) 0.73 × 106 m/s (B) 3.0 × 108 m/s (C) 2.92 × 106 m/s (D) 1.46 × 106 m/s 33. Sodium and copper have work functions 2.3eV and 4.5eV respectively. Then the ratio of the threshold wavelength is nearest to (A) 1: 2 (B) 4: 1 (C) 2: 1 (D) 1: 4 34. The bonding energy per nucleon of 3 7Li& 2 4He are 5.60MeV and 7.06MeV respectively. In the nuclear reaction 3 7Li + 1 1H → 2 4He + 2 4He + Q the value of