# Aircraft Performance Questions and Answers – Characteristics of Atmosphere

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This set of Aircraft Performance Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of Atmosphere”.

1. What is the ideal gas equation?
a) P=nRT
b) PV=nRT
c) PV=ρRT
d) Pρ=RT

Explanation: The ideal gas equation is PV=ρRT, where
P=pressure of gas (Units=N/m2)
V=volume of gas (Units=m3)
ρ=density of gas (Units=Kg/m3)
R=universal gas constant (Units=Nm/kg-K)
T=temperature of gas (Units=K).

2. Between the poles and the equator the mean global temperature roughly follows a sine curve.
a) True
b) False

Explanation: Between the poles and the equator the mean global temperature roughly follows a sine curve. This is due to the changes of temperature near the equator and the poles. At the equator the mean seasonal variation is small and the mean temperature is high whereas at the poles the mean seasonal variation is large and the mean temperature is low.

3. Which of the following is the major reason for the global atmosphere pressure distribution?
a) Convective air flow
b) Conductive air flow
d) Conductive and radiation air flow

Explanation: The convective air flow is the major reason for the global atmosphere pressure distribution. The Coriolis forces cause the air flow to swirl and create a series of convectional current cells which results in the general pattern of high and low pressure region over the surface of the earth.

4. What is meant by Coriolis force?
a) An earth force that tends to deflect the moving objects on earth
b) An earth force that tends to vary the temperature
c) An earth force that tends to vary the pressure
d) An earth force that tends to vary the gravitational force

Explanation: Coriolis force is an earth force that acts perpendicular to the direction of motion and to the axis of rotation. This force tends to deflect moving objects to the left in the southern hemisphere and towards the right in the northern hemisphere.

5. Which of the following holds a correct relation between pressure, temperature and altitude?
a) Pressure increases, temperature decreases, altitude increases
b) Pressure decreases, temperature decreases, altitude increases
c) Pressure decreases, temperature increases, altitude increases
d) Pressure decreases, temperature decreases, altitude decreases

Explanation: As the pressure decreases there will be a temperature decreases during an increase in altitude. This is based on ideal gas equation PV=nRT where,
P=pressure of gas (Units=N/m2)
V=volume of gas (Units=m3)
ρ=density of gas (Units=Kg/m3)
R=universal gas constant (Units=Nm/kg-K)
T=temperature of gas (Units=K).

6. What are the percentages of nitrogen, oxygen, argon and carbon dioxide in atmosphere?
a) 78%, 21%, 0.9%, 0.03%
b) 75%, 24%, 0.7%, 0.03%
c) 71%, 28%, 0.9%, 0.04%
d) 75%, 24%, 0.9%, 0.05%

Explanation: The percentages of nitrogen, oxygen, argon and carbon dioxide in atmosphere are 78%, 21%, 0.9%, 0.03%. The atmosphere also consists of other inert gases, dust particles, water vapor and moisture in minute quantities.

7. What is the value of characteristic gas constant(R) in Nm/kg-K?
a) 287.05287
b) 2.8705287
c) 2870.5287
d) 2.8705287

Explanation: The value of characteristic gas constant(R) is 287.05287 Nm/kg-K and the value of universal gas constant (R0) is 8.3145 J/mol. The relation between them is R=$$\frac{R0}{M}$$ , where R0 is universal gas constant; R is characteristic gas constant and M is molecular weight of the substance.

8. The ratio of specific heats (γ) of air is _________
a) 1.6
b) 1.7
c) 1.4
d) 1.8

Explanation: The ratio of specific heats (γ) of air is 1.4. Ratio of specific heats is the ratio of specific heat of air at constant pressure to the specific heat of air at constant volume, i.e. $$\frac{C_p}{C_v}$$=γ. Cp of air is 1.008 kJ/kg-K; Cv of air is 0.721 kJ/kg-K at standard levels. So γ=$$\frac{1.008}{0.721}$$=1.4.

9. At the equator the mean seasonal variation is small and the mean temperature is high whereas at the poles the mean seasonal variation is large and the mean temperature is low.
a) True
b) False

Explanation: At the equator the mean seasonal variation is small and the mean temperature is high whereas at the poles the mean seasonal variation is large and the mean temperature is low. This is due to the change in temperature with respect to the altitude of the atmosphere. It is almost similar to a sine graph.

10. Regions of low pressure, cyclones and high pressure, anti-cyclones are formed by effects of convection currents in the atmosphere.
a) True
b) False

Explanation: Regions of low pressure, cyclones and high pressure, anti-cyclones are formed by effects of convection currents in the atmosphere. This is caused due to the air transporting from higher temperature regions to the lower temperature regions.

11. According to ISA atmospheric model what is the value of datum atmospheric pressure in N/m2?
a) 101325
b) 101335
c) 101336
d) 101326 