When the metal is heated, the metal gain thermal energy and molecules gain kinetic energy vibrate more vigorously. This will result in the molecules moving further apart from each other, thus the metal expand. However, metal B has a greater expansivity, thus the molecules in the metal move more vigorously than the molecules of metal A. Thus, metal B expands more than metal A, causing the bimetallic strip to bend.
When water is being splashed at the metal, the metal lose thermal energy to the water and molecules in the metal lose kinetic energy. Thus, metal A And Metal B both lose thermal energy. However, as metal B has a greater expansivity, the bimetallic strip straitened