A student notices that the rumble of distant thunder seems to reach her ears sooner on a hot summer afternoon than on a cold winter night.
(i) Explain why an increase in air temperature causes the sound of thunder to be heard sooner, even though the distance of the lightning flash from the observer is the same.
(ii) If the average temperature of the air rises from 0∘C to 30∘C, qualitatively describe how the density of the air changes and how this change affects the speed of sound.
(iii) Suggest one additional atmospheric factor, apart from temperature, that can further influence the speed of sound between the source and the observer and briefly explain its effect.