TEFA Competitive Entrance Exams

Aug. 24, 2024, 12:49 p.m.
HIHS2023USS ELAH WILFRIED
Question 15 the explanation given is not true. The circumference of the circle passess through the point (0,2)

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- Aug. 24, 2024, 12:51 p.m.
  HIHS2023USS ELAH WILFRIED
  2010
  
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Aug. 19, 2023, 2:50 p.m.
NKENFACK BLONDEL
CORRECTION

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Aug. 15, 2023, 3:44 p.m.
NKENFACK BLONDEL
Option C) states that “there is entropy variation when there is heat exchange.” This statement is not necessarily incorrect, as there can indeed be a change in entropy when there is heat exchange between a system and its surroundings. However, the question specifically refers to an adiabatic process, which means that there is no heat exchange between the system and its surroundings. In this case, option C) is not relevant to the situation described in the question.

In an adiabatic and irreversible expansion of an ideal gas, there is always a change in entropy due to the irreversibility of the process, even if there is no heat exchange with the surroundings. So, the correct answer to the question is option A) “there is always entropy variation.”

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Aug. 15, 2023, 5:11 a.m.
NKENFACK BLONDEL
Momentum is conserved in an isolated system, but the question you asked was about an isolated system where only one quantity is always conserved. In this case, the correct answer is A) Energy. The law of conservation of energy states that the total energy of an isolated system remains constant over time. This means that energy can neither be created nor destroyed, but can only be transformed or transferred from one form to another.

On the other hand, the conservation of momentum is a major law of physics which states that the momentum of a system is constant if no external forces are acting on the system. It is embodied in Newton’s First Law or The Law of Inertia. This means that the total momentum of an isolated system will remain constant as long as there are no external forces acting on it.

In summary, both energy and momentum can be conserved in an isolated system, but the question specifically asked for only one quantity that is always conserved in an isolated system, and the correct answer to that question is A) Energy.

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Aug. 9, 2023, 5:56 p.m.
NKENFACK BLONDEL
The carbon-fluorine bond is stronger than the carbon-oxygen bond. The bond dissociation energy (BDE) of a carbon-fluorine bond can be up to 130 kcal/mol, which is higher than other carbon-halogen and carbon-hydrogen bonds 1. On the other hand, the C-O bond strength is also larger than C-N or C-C. For example, bond strengths are 91 kilocalories (380 kJ)/mol (at 298 K) in methanol 2. This means that the carbon-fluorine bond is stronger than the carbon-oxygen bond.

HENCE C IS THE CORRECT OPTION

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Aug. 9, 2023, 5:24 p.m.
NKENFACK BLONDEL
CORRECTION:

Charge density is the ratio of the charge of an ion to its volume. The charge density of an ion is determined by its size and charge. The smaller the ion and the greater its charge, the higher its charge density will be. Oxygen and sulfur are both in group 16 of the periodic table, and they both commonly form ions with a -2 charge. However, sulfur has a larger atomic radius than oxygen1, which means that its volume is larger. As a result, the charge density of sulfur is lower than that of oxygen.

HENCE BY CONCLUSION THE CORRECT ANSWER IS D

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Aug. 9, 2023, 2:26 a.m.
NKENFACK BLONDEL
CORRECT OPTION IS A

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Aug. 2, 2023, 3:52 p.m.
NKENFACK BLONDEL
here the answer is D

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- Aug. 5, 2023, 11:56 a.m.
  tandutabi
  D
  
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- Aug. 23, 2023, 4:38 p.m.
  ARNAUD
  YES YOU ARE CORRECT
  
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