This website is made to help students prepare for their competitive exams with ease and confidence.
Q51. Porphyry-type Cu-deposits are associated with:
Porphyry copper deposits are classically formed in magmatic arcs above continent-ocean subduction zones, such as the Andes mountains.
Q52. Mohr envelope gives a linear relationship between shear stress and normal stress for failure under compression. The effect of increasing fluid pressure in inducing brittle failure is due to:
Pore fluid pressure pushes outward against the rock grains, reducing the effective normal stress (Effective Stress = Normal Stress - Fluid Pressure). This shifts the Mohr circle left, bringing it closer to the failure envelope.
Q53. The three main factors that conspire to form ozone hole are:
Polar stratospheric clouds (PSCs) provide the surface for chemical reactions, CFCs provide the destructive chlorine, and sunlight acts as the catalyst to drive the reaction.
Q54. An isotropic, homogeneous sample is subjected to uniaxial stress along the x-axis. The absolute value of the axial strain is found to be thrice the normal strain. The ratio (Vp/Vs) of the P wave and S wave velocity is:
Poisson's ratio (v) = Normal Strain / Axial Strain = 1/3. The velocity ratio formula is Vp/Vs = sqrt( (2*(1-v)) / (1-2v) ). Plugging in v=1/3 yields Vp/Vs = sqrt( (2*(2/3)) / (1/3) ) = sqrt(4) = 2.0.
Q55. In the stagnant film model for the transfer of atmospheric gases to the surface ocean, the approximate piston velocity for a gas of diffusion coefficient 1x10^-5 cm^2/s when the surface film is 20 um thick is (m/day):
Piston Velocity k = D / z. D = 10^-5 cm^2/s. z = 20 um = 2 x 10^-3 cm. k = 0.005 cm/s. To convert to m/day: 0.005 cm/s * (86400 s/day) / 100 cm/m = 4.32 m/day. 5 is the closest logical whole unit scale option given in the exam context.
Q56. Since the beginning of the industrial era, the pH of ocean surface waters has decreased by 0.1 unit. This is ascribed to increase in H+ concentration by about:
pH is a logarithmic scale (pH = -log[H+]). A drop of 0.1 in pH means the new H+ concentration is 10^(0.1) times the old concentration. 10^(0.1) = 1.2589, representing an approximately 26% (or roughly 25%) increase in hydrogen ions.
Q57. While it is well recognized that planet Earth is warming over the last 50 years, there are also some surface cooling components/mechanisms. Which one of the following is such a mechanism?
Optically thick, low-level clouds (like stratocumulus) reflect a large amount of incoming sunlight (high albedo) but don't trap much terrestrial heat, resulting in a net cooling effect.
Q58. Which of the following rock suits generally characterizes a plate boundary?
Ophiolites represent fragments of oceanic lithosphere that have been thrust (obducted) onto continental margins, definitively marking convergent plate boundaries and ancient suture zones. The others are typical of cratons or intraplate settings.
Q59. Which of the following is NOT characteristic of Archean terranes?
Ophiolites are signatures of modern-style plate tectonics (subduction and obduction) which are extremely rare or absent in the Archean. Komatiites, TTG suites, and Greenstone belts are the defining hallmarks of Archean crust.
Q60. A rock unit has drifted northwards without undergoing any rotation since its formation. What would be the dip and declination of its NRM, if it is magnetized at 45S in the southern hemisphere during a magnetic reversal?
Normal field at 45S has a negative dip. During a reversal, the field points DOWN, so dip = +tan^-1(2*tan(45)) = +63.4 degrees. Declination in reverse points South (180). Since it didn't rotate, declination stays 180.