SSC GD 2025 PYQ — Question 34

The correct answer is option 2 i.e. First law.

• The First Law of Thermodynamics states that energy cannot be created or destroyed in an isolated system; it can only be transferred or converted from one form to another.

• It is essentially a restatement of the law of conservation of energy.

• Mathematically expressed as:

  $ΔQ=ΔW+ΔU$

  where:

  • ΔQ = heat added to the system

  • ΔW = work done by the system

  • ΔU = change in internal energy of the system

• The First Law helps in understanding the principle of conservation of energy.

• In contrast, the Second Law of Thermodynamics states that heat flows naturally from a body at a higher temperature to a body at lower temperature, unless external work is applied.

Other Options:

• Third Law of Thermodynamics: Relates to absolute zero temperature.
• It states that 'As the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches zero.'

• Zeroth Law of Thermodynamics: Defines temperature and thermal equilibrium.
• It states that 'If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.'

• Second Law of Thermodynamics: Deals with entropy (disorder or randomness).

• It states that 'In any energy transfer or transformation, the total entropy of a closed system will always increase over time.'