GEARS End-of-Year Practice Exam 2026 - Free Practice Questions and Study Guide

Direct contact heat transfer, or conduction, is what happens when you heat popcorn on a hot plate. The hot plate transfers heat to the pan by touching it, and that heat travels through the pan into the kernels (and the oil) that are in contact with it. This direct transfer raises the kernel’s internal water until it boils and builds pressure, causing the kernel to pop. Radiation would involve heat reaching the kernels as electromagnetic waves from a hot surface, which isn’t the main path here, and convection would require moving air or liquid to carry heat, which is not the dominant mechanism in a hot-pan setup. Evaporation is a process, not a mode of heat transfer. So conduction best explains the heat transfer to the popcorn.