Meteorology
Meteorology is the study of why the atmosphere does what it does, and questions test both physical reasoning and standard definitions. Build your knowledge from the ground up.
Key concepts: the standard atmosphere and the ISA lapse rate (about 2°C per 1 000 ft); pressure, density and temperature relationships; the coriolis effect and geostrophic wind; the difference between true and indicated altitude and the effect of temperature on the altimeter (cold air - the altimeter over-reads, so you are lower than indicated); stability and instability; cloud types and their associated weather; thunderstorms and their hazards (downbursts, microbursts, hail, icing, lightning); icing types (rime, clear, mixed) and their formation conditions; fog types (radiation, advection, frontal, upslope); and the standard pressure settings (QNH, QFE, QNE) and their use.
Traps: confusing QNH and QFE; forgetting that cold temperatures make the altimeter over-read; assuming a warm front produces more violent weather than a cold front; and mixing wind direction conventions (meteorological wind is from the direction).
Worked example: an aircraft at an indicated altitude of 5 000 ft in air colder than ISA. The altimeter over-reads, so the true altitude is lower than 5 000 ft. Rule of thumb: high to low, look out below - flying from high pressure to low pressure, or into colder air, without resetting the altimeter puts you lower than indicated.