Which of the following methods make use of infra-red lamp in the determination of water content of soils?
- ACalcium carbide method
- BPycnometer method
- CAlcohol method
- DTorsional balance methodCorrect
Solution
Concept
The torsion balance moisture meter dries the soil sample with an infra-red lamp and reads the moisture directly.
Formula
w = (Ww / Ws) × 100
Step-by-step solution
1. Calcium carbide method uses CaC₂, which reacts with water and gives acetylene gas pressure. 2. Pycnometer method uses the specific gravity and weighing of the soil-water mixture. 3. Alcohol method burns methylated spirit mixed with the soil to dry it. 4. The torsion balance method uses an infra-red lamp to dry the sample and a torsion balance to read moisture. 5. So the answer is D.
Explanation
In the torsion balance method, an infra-red lamp heats and dries the soil sample quickly. The torsion balance shows the loss of weight directly as moisture content. This makes the method fast and suitable for field work.
Why the other options are wrong
A: Uses calcium carbide and gas pressure, not heat. B: Uses a pycnometer and specific gravity, not a lamp. C: Dries the soil by burning alcohol, not with an infra-red lamp.
Shortcut
Infra-red lamp = Torsion balance moisture meter.
Common mistake
Confusing it with the oven-drying or alcohol burning methods, which also use heat.
Correct answer: D) Torsional balance method