Which method is used during indirect liquid level measurement? | Agrigyan

A bactericidal agent or treatment directly causes the lethal destruction and killing of bacteria. Ionizing radiation (gamma rays from Cobalt-$60$, electron beams, or X-rays) directly damages microbial DNA and generates lethal free radicals (radiolysis of water), destroying bacterial cells lethally (bactericidal). Membrane filtration physically removes cells (not killing), while freeze-drying and deep freezing are bacteriostatic (inhibiting metabolic activity without necessarily killing cells).

Option analysis:

• Membrane filtration: Physical separation/removal process, not bactericidal.
• Freeze-drying: Preservation technique that preserves bacterial viability (used to store culture stocks).
• Ionizing radiation: Correct, causes irreversible DNA strand breaks leading to bacterial cell death.
• Deep freezing: Bacteriostatic preservation method; bacterial cells can survive frozen storage.

In a fire tube boiler, hot combustion gases pass through tubes surrounded by water inside the boiler shell. The Locomotive boiler (along with Cochran, Lancashire, and Cornish boilers) is a classic fire tube boiler. In contrast, Babcock and Wilcox, Benson, and Stirling boilers are water tube boilers where water circulates inside the tubes while hot flue gases pass externally.

Option analysis:

• Babcock and Wilcox boiler: High-pressure water tube boiler.
• Locomotive boiler: Correct, horizontal multi-tubular externally fired fire tube boiler.
• Benson boiler: Supercritical once-through water tube boiler.
• Stirling boiler: Bent-tube water tube boiler.

The Thermal Death Time (TDT) curve is a semilogarithmic plot representing the lethal effect of temperature on a specific microorganism. The logarithm of heating time required to achieve commercial sterility or a specified log-reduction (log of TDT or F-value) is plotted on the vertical logarithmic axis against lethal processing temperature on the horizontal linear axis. The slope gives the z-value.

Option analysis:

• Time vs temperature: Linear plot, does not linearize the exponential thermal destruction kinetics.
• Temperature vs log (time): Correct, semilog plot of lethality time versus heating temperature.
• Time vs log (number of survivors): This defines the survivor curve or decimal reduction time ($D$-value) plot at constant temperature.
• Temperature vs Time: Linear plot, not the standard TDT semilog representation.