A

Step 1: As the heated metal cone is placed on the mica sheet, it heats the mica due to conduction. Mica, being a good insulator, retains heat to some extent when the heated cone is placed on it.
Step 2: The cone begins to roll due to a difference in expansion rates. The copper plate is a good conductor of heat and allows for quicker dissipation of heat compared to glass. This keeps the bottom of the cone cooler than the apex.
Step 3: As the apex is heated more than the base, it expands more, and as a result, creates a slight slope when resting on the mica. This causes the cone to roll away from the apex due to gravitational forces acting on the uneven distribution of heat.
Step 4: If there were a glass sheet instead of a copper plate below the mica, the scenario would differ significantly. Glass does not conduct heat as efficiently as copper, so the heat would not dissipate as quickly.
Step 5: Consequently, the heated cone would not create enough differential expansion which means it would not roll as effectively. Instead, it might just sit stationary unless the temperature of the apex exceeds a certain threshold causing other factors such as thermal expansion to act unevenly.
Therefore, with a copper plate, the cone rolls because of efficient heat dissipation; with glass, it remains mostly stationary due to insufficient heat conduction.