The variation between a high air temperature and a low temperature that occurs during the same day is called _______ temperature.

Correct — B. The gap between the highest and the lowest air temperature recorded at a place on the same day is the diurnal range of temperature. Diurnal means within a single day.

The maximum normally comes in the early afternoon, a couple of hours after peak insolation, and the minimum just before sunrise.

Clear skies, dry air and bare sandy surfaces widen the range because heat escapes fast at night. Cloud, humidity and the nearness of the sea narrow it → option (b).

Why the others are wrong

• (a)
  wet bulb — Wet-bulb temperature is read from a thermometer whose bulb is wrapped in moist cloth. It measures evaporative cooling and therefore humidity, not a spread between two moments of the day.
• (c)
  annual — Annual range is the same idea stretched over a year — the difference between the mean temperature of the warmest and the coldest month. The question fixes the period at one day.
• (d)
  durian — Durian is a tropical fruit. It is placed here purely as a sound-alike for diurnal, and it is a reminder to read the options rather than recognise them.

Temperature is described at two time scales. The diurnal range compares the maximum and minimum of one day, the annual range compares the warmest and coldest months.

What widens the diurnal range is anything that lets the surface heat and cool quickly: cloudless skies, low humidity, sandy or rocky ground, and distance from the sea.

Deserts are the extreme case, scorching by day and cold by night. Coastal and cloudy places sit at the other end, because water and water vapour hold heat.

Key facts

• The diurnal range of temperature is the difference between the maximum and the minimum temperature of the same day.
• Deserts show very large diurnal ranges because dry, cloudless air lets surface heat escape rapidly at night.
• The annual range compares the mean temperatures of the warmest and coldest months.
• Wet-bulb temperature is read from a thermometer covered by a moist cloth and reflects humidity.

Common traps

• Choosing annual because the phrase range of temperature is more familiar in that form.
• Choosing wet bulb because it sounds technical, when it reports humidity rather than a temperature spread.
• Not noticing that the question has already fixed the period with the words the same day.

No directly related past PYQ was found.