21. Which of the following statements is true about the first law of thermodynamics?
A) Energy cannot be created or destroyed, only transformed from one form to another
B) The amount of heat transferred is directly proportional to the temperature difference between two objects
C) The entropy of a system always decreases over time
D) The internal energy of a system is constant if there is no heat transfer or work done
22. Which of the following statements is true about the second law of thermodynamics?
A) The entropy of a system always decreases over time
B) The total energy of a closed system is constant
C) Heat cannot flow from a colder object to a warmer object without the input of external work
D) The efficiency of a heat engine is always 100%
23. The maximum efficiency of a heat engine operating between two temperatures is given by:
A) 1 – T1/T2
B) T1/T2
C) (T2 – T1)/T2
D) (T2 – T1)/T1
24. Which of the following materials has the highest thermal conductivity?
A) Air
B) Water
C) Copper
D) Wood
25. The transfer of heat through a material without any flow of the material itself is called:
A) Conduction
B) Radiation
C) Convection
D) Insulation
