Why do opaque materials become warmer when light shines on them?

Opaque materials absorb all the light that shines on them.  None of it comes out the other side.  That's why they're opaque.

Opaque materials become warmer when light shines on them, because they absorb the energy carried by the light that shines on them.  (According to the law of Conservation of Energy, that energy has gotta go somewhere.)

i would say the answer is food.

hope this !

current and voltage can both be different in different parts of a circuit so it matters where you place the ammeter and voltmete