How does the MIE of a solid change as particle size decreases?

How does the MIE of a solid change as particle size decreases?

• A. It increases
• B. It remains constant
• C. It decreases
• D. It varies unpredictably

Answer: (C)

MIE is the energy required to ignite a material. When particle size gets smaller, the particle has less mass and thus a smaller heat requirement to reach the ignition temperature. The higher surface area to volume ratio of tiny particles also means heat transfer into the particle is more efficient, helping it reach ignition more quickly. Because both reduced mass and more rapid heating make ignition easier, the minimum ignition energy decreases as particle size decreases. The other options don’t fit because a constant MIE ignores the effect of mass, an increasing MIE would imply ignition becomes harder with smaller particles, and an unpredictable variation ignores the clear trend from thermal mass and heat transfer considerations.

MIE is the energy required to ignite a material. When particle size gets smaller, the particle has less mass and thus a smaller heat requirement to reach the ignition temperature. The higher surface area to volume ratio of tiny particles also means heat transfer into the particle is more efficient, helping it reach ignition more quickly. Because both reduced mass and more rapid heating make ignition easier, the minimum ignition energy decreases as particle size decreases. The other options don’t fit because a constant MIE ignores the effect of mass, an increasing MIE would imply ignition becomes harder with smaller particles, and an unpredictable variation ignores the clear trend from thermal mass and heat transfer considerations.