## 08.1. physics of the atmosphere

__Question Number 1:__

The ISA

Option A: assumes a standard day.

Option B: is taken from the equator.

Option C: is taken from 45 degrees latitude.

__Correct Answer:__

is taken from 45 degrees latitude.

__Explanation:__

The properties of a standard day are related to sea level at latitude 45 degrees latitude.

__Question Number 2:__

At higher altitudes as altitude increases, pressure

Option A: decreases at constant rate.

Option B: decreases exponentially.

Option C: increases exponentially.

__Correct Answer:__

decreases exponentially.

__Explanation:__

Pressure decreases. But the rate of decrease reduces with altitude. At 18000 ft, half the pressure is lost already, and there is still another 40,000ft or so to go.

__Question Number 3:__

When the pressure is half of that at sea level, what is the altitude?

Option A: 12,000 ft.

Option B: 18,000 ft.

Option C: 8,000 ft.

__Correct Answer:__

18,000 ft.

__Explanation:__

Just one of those facts you have to learn - but it is quoted in just about every text book on CAA reading list.

__Question Number 4:__

If gauge pressure on a standard day at sea level is 25 PSI, the absolute pressure is

Option A: 39.7 PSI.

Option B: 10.3 PSI.

Option C: 43.8 PSI.

__Correct Answer:__

39.7 PSI.

__Explanation:__

Absolute pressure = gauge pressure plus atmospheric pressure. Atmospheric pressure at seallevel = 14.7 PSI.

__Question Number 5:__

Pressure decreases

Option A: inversely proportional to temperature.

Option B: proportionally with a decreases in temperature.

Option C: Pressure and temperature are not related.

__Correct Answer:__

proportionally with a decreases in temperature.

__Explanation:__

Temperature and volume are directly proportional - Charles' Law.

__Question Number 6:__

As air gets colder, the service ceiling of an aircraft

Option A: reduces.

Option B: increases.

Option C: remains the same.

__Correct Answer:__

increases.

__Explanation:__

As air gets colder it gets denser. Lift increases (remember the lift equation has density) and the engines produce more thrust - so it can climb higher.

__Question Number 7:__

What is sea level pressure?

Option A: 1012.3 mb.

Option B: 1013.2 mb.

Option C: 1032.2 mb.

__Correct Answer:__

1013.2 mb.

__Explanation:__

Learn the ISA sea level quantities, in all units.

__Question Number 8:__

How does IAS at the point of stall vary with height?

Option A: It decreases.

Option B: It is practically constant.

Option C: It increases.

__Correct Answer:__

It is practically constant.

__Explanation:__

The stalling IAS at altitude is practically the same as it is at sea level. That's because IAS is not corrected for density.

__Question Number 9:__

What is the lapse rate with regard to temperature?

Option A: 4°C per 1000 ft.

Option B: 1.98°C per 1000 ft.

Option C: 1.98°F per 1000 ft.

__Correct Answer:__

1.98°C per 1000 ft.

__Explanation:__

The lapse rate is approximately 2°C per 1000 feet (in the troposphere).

__Question Number 10:__

Standard sea level temperature is.

Option A: 20 degrees Celsius.

Option B: 0 degrees Celsius.

Option C: 15 degrees Celsius.

__Correct Answer:__

15 degrees Celsius.

__Explanation:__

15 degrees C is standard sea level temperature.

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