Competitive Exams: Physics MCQs (Practice-Test 29 of 35)

  1. A plan em wave E2 = 100 cos (6 × 108t + 4x) V/m propagates in a medium of dielectric constant

    1. 1.5

    2. 2.0

    3. 2.4

    4. 4.0

  2. In a mass spectrometer, the velocity filter employs electric field E and a perpendicular magnetic field B. The deflecting magnetic field perpendicular to the. Beam is ‘B’ Ions with similar charges ‘q’ and mass numbers m1 and m2 pass through the filter. After a 180 turn in the deflecting field, the separation between them will be

    1. E (m2 − m1)/q B B'

    2. 2E (m2 − m1)/q B B'

    3. Fq (m2 − m1)/BB'

    4. 2Eq (m2 − m1) B B'

  3. The emf of a thermocouple, one junction of which is at 0 degree C is given by E = at + bt2 The Peltier coefficient is given by (T is in Kelvin)

    1. T 2at + b

    2. T 2a + bt

    3. T a + bt

    4. T a + 2bt

  4. A cyclotron having segments of radius 50 cm is used for accelerating hydrogen nuclei. The polarity of the segments is reversed 5 × 107 times per second. The energy of the incoming proton beam is (mass of the proton = 1.673 × 10 − 24 gm, 1.6 × 10 − 12 erg = l e V)

    1. 3.225 MeV

    2. 32.25 Me V

    3. 3225 MeV

    4. 0.3225 Me V

  5. A copper disc of 10 cm radius makes 1200 revolutions per minute with its plane perpendicular to a magnetic field, If the induced emf between the centre and edge of the disc is 6.28 millivolt, then the intensity of the field is

    1. 100 Oersted

    2. 80 Oersted

    3. 60 Oersted

    4. 50 Oersted

  6. An election (mass = me) and a proton (mass = 1836 me) are moving with the same speed. The ratio of their deBroglie wavelengths l electron/l proton will be

    1. 1

    2. 1836

    3. 1\1836

    4. 918

  7. A hydrogen-like atom a has a p-meson of mass 200 times that of an electron, bound to the proton. The radius of the first Bohr orbit of this moronic atom will be

    1. equal to that of H

    2. 10 times that of H

    3. 200 times that of H

    4. 1/200 times that of H

  8. The frequency of the Ka line of characteristic X-ray spectrum is proportional of (Z = atomic number)

    1. Z

    2. Z1/2

    3. Z2

    4. Z3/2

  9. The wavelength of the photoelectric threshold for silver is lo. The energy of the electron elected from the surface of silver by an incident light of wavelength l l (< lo) will be

    1. hC (l0 − l)

    2. hC/l0 l-

    3. h/C (1/l l/1 − 0)

    4. hC (l0 l) l − 0l

  10. Consider the following statements. In Compton scattering, the shift in the wavelength of the incident photon depends upon the

    1. wavelength of the incident photon.

    2. nature of the scattering substance.

    3. angle of scattering.

    Of these statements

    1. 1 and 2 are correct

    2. 1 and 3 are correct

    3. 3 alone is correct

    4. 2 and 3 are correct

  11. If 20% of a radioactive isotope decays in 5 days, then the amount of the original material left after 15 days will be approximately

    1. 20%

    2. 50%

    3. 60%

    4. none of the above

  12. If the mass of a particle is three times its rest mass, then the speed at which the particle is moving is (C = velocity of light)

    1. 8/3 C

    2. 8/9 C

    3. 8/9 C

    4. 3C

  13. Which one of the following is a set of Magic Numbers?

    1. 1, 2, 8, 16, 20, 28

    2. 2, 8, 16, 20, 28, 50

    3. 8, 28, 50, 82, 100, 126

    4. 2, 8, 20, 28, 50, 82, 126

  14. The average binding energy per nucleon is 7.6 Me V for a heavy nucleous such as uranium while it is 8.5 Me V for nuclei with mass numbers around 110. The energy released in binary fission of U − 235 by slow neutrons will be approximately

    1. 7.6 MeV

    2. 8.5 MeV

    3. 212.4 MeV

    4. 235 MeV

  15. The beta decay of the neutron is explicitly given by

    1. n-p + e

    2. n-p + e + ue

    3. n-p + e + ue

    4. n-p + e + g