Thermodynamics and Heat MCQs for MDCAT

Correct answer: C. Kelvin

The SI base unit of temperature is the kelvin (K), the absolute temperature scale used in scientific measurement.

Correct answer: A. In system A

The change in internal energy corresponds to the net area enclosed within a cyclic process on a P-V diagram; a larger enclosed area (system A) indicates a greater net change associated with that cycle.

Correct answer: C. Change in temperature

For an ideal gas, the change in internal energy depends only on the change in temperature, since internal energy is a function of temperature alone for an ideal gas.

Correct answer: A. 27 oC

Using the Carnot efficiency formula η = 1 − Tc/Th with Th = 600 K (327°C) and η = 50%, solving gives Tc = 300 K = 27°C.

Correct answer: A. Q = W

For an isothermal process, since temperature (and thus internal energy) doesn't change, the first law of thermodynamics simplifies to Q = W.

Correct answer: A. Room temperature

Thermistors with a negative temperature coefficient are most sensitive and accurate for measuring temperatures near room temperature, where their resistance changes most significantly with small temperature variations.

Correct answer: D. 0.0821 dm³-atm

One mole of an ideal gas at 273.16 K and one atmospheric pressure and its temperature is increased by 1K, then it will absorb 0.0821 dm³-atm of energy, dm³-atm is the unit of energy in this situation.

Correct answer: D. Less than double

During an isobaric process, the pressure of the gas remains constant. However, the volume of the gas is directly proportional to its temperature (according to Charles' law). When the temperature increases from 150°C to 300°C, the volume of the gas will increase. However, it will not double because the relationship between volume and temperature is not linear. As the temperature increases, the gas molecules gain more kinetic energy and move with higher speed, leading to increased collisions with the container walls. This causes an increase in pressure, which in turn affects the volume. As a result, the volume will increase but not double.

Correct answer: B. pV=nRt

PV=nRTP = Pressure of the gasV = Volume of the gasn = Number of moles of gasR = Universal gas constant (8.314 J/mol·K)T = Temperature in KelvinThis equation describes the relationship between pressure, volume, and temperature for an ideal gas.

Correct answer: B. 0

In an adiabatic process, the value of heat energy (\(Q\)) is zero. This is because, by definition, an adiabatic process is one in which no heat is exchanged between the system and its surroundings, meaning the system is perfectly insulated. Therefore, \(Q = 0\) in an adiabatic process, and any changes in internal energy are due solely to work done by or on the system.

Correct answer: D. Charles law

Charles' Law states that, at constant pressure, the volume of a fixed mass of gas is directly proportional to the absolute temperature. This can be expressed mathematically as:V ∝ TorV = kTwhere V is the volume, T is the absolute temperature, and k is a constant

Correct answer: A. Germanium and silicon

Germanium and silicon, which are semiconductors, exhibit a negative temperature coefficient of resistance. This means that their electrical resistance decreases as temperature increases.Here's why:- Germanium and silicon have a negative temperature coefficient because as temperature increases, the vibrations of the atoms (thermal energy) help to excite electrons into the conduction band, increasing conductivity and reducing resistance.- Iron (a metal) has a positive temperature coefficient, meaning its resistance increases with temperature.- Copper (a metal) also has a positive temperature coefficient, meaning its resistance increases with temperature.